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is a structural unit of the kidney, which consists of the renal corpuscle and renal tubules. In the renal corpuscle, blood is filtered, and with the help of the tubules, reverse absorption (reabsorption) occurs. Blood passes through this system many times every day, and as a result of the processes described above, primary urine is formed.

Subsequently, it goes through several more stages of purification, dividing into water, which returns back to the blood, and metabolic products, which are excreted into the environment along with urine.

Ultimately, from the 120 liters of glomerular ultrafiltrate that passes through the nephrons daily, about 1-2 liters of secondary urine are formed. If the excretory system is healthy, the formation of primary urine and its filtration occurs without any complications.

What is GFR calculation used for?

When a disease occurs, nephrons fail faster than new ones can be formed, therefore, the kidneys cope less well with their cleansing function. In order to assess how much this indicator differs from normal values, speed analysis is used. glomerular filtration or - Tareeva.

He is one of the main diagnostic methods, which allows you to assess the filtration capacity of the kidney. With its help, you can calculate the volume of glomerular ultrafiltrate that is formed in a certain unit of time.

The results of this analysis are combined with the rate of purification of blood serum from the protein breakdown product - creatinine, and an assessment of the filtration abilities of the kidneys is obtained.

Glomerular filtration rate depends on the following factors:

the amount of plasma that enters the kidneys. Normally this is 600 ml per minute in an adult;
pressure at which filtration occurs;
filtered surface area.

What diseases can be diagnosed

Analysis of the Reberg-Tareev test is used when various pathologies are suspected excretory system. If this figure is less than normal, this means massive death of nephrons. This process can indicate acute and chronic renal failure.

Since GFR can decrease not only due to damage structural units kidneys, but also due to third-party factors, this phenomenon is also observed with hypotension, heart failure, prolonged vomiting and diarrhea, hypothyroidism, diabetes insipidus, as well as difficulty in the outflow of urine due to a tumor or inflammation in the urinary tract.

An increase in GFR is observed in idiopathic acute and chronic glomerulonephritis, diabetes mellitus, arterial hypertension, some autoimmune diseases.

Fine GFR values are constant, in the range of 80-120 ml/min., and only with age this figure can decrease for natural reasons. If these numbers decrease to 60 ml/min, this indicates renal failure.

What formulas are used to calculate GFR?

In medicine, the meaning associated with is most often used - this method is considered the simplest and most convenient for medical diagnosis. Since it is excreted through the glomeruli only by 85-90%, and the rest through the proximal tubules, calculations are carried out with an indication of the error.

The lower its value, the correspondingly higher the GFR rate. Direct measurement of insulin filtration rate is too expensive for medical diagnosis and is used mainly for scientific purposes.

The patient's blood and urine are used for the analysis. It is especially important to collect urine strictly within the allotted time period. Today there are 2 options for collecting material:

Two hourly portions of urine are collected, and in each sample the minute diuresis and the concentration of the end product of protein breakdown are examined. The result is two GFR values.
Less commonly used, in which the average creatinine clearance is determined.

On a note! The situation with blood is simpler - it remains unchanged for a long time, so this sample is taken as standard - in the morning on an empty stomach.

Standard formula

(up x Vn) / (Ср x Т),

where Vn is the volume of urine over a fixed period of time, Cp is the concentration of creatinine in the blood serum, T is the time during which urine is collected in minutes.

Cockcroft-Gault formula

[(140 - (number of years) x (weight, kg)] / (72 x serum creatinine concentration, mg/dL)

The result of the calculation using this formula is true for an adult man; for women, the result must be multiplied by a coefficient of 0.85.

Criatinine clearance formula

[(9.8 - 0.8) x (age - 20)]/ serum creatinine concentration, mg/min

For women in this case, you also need to apply a coefficient of 0.9.

You can use one of the online calculators that will help you calculate your creatinine clearance. One of them can be found at this link.

Since GFR depends on the rate of clearance of creatinine from blood plasma, it is also calculated manually using the formula:

(urine creatinine concentration x urine volume over time)/(plasma creatinine concentration x urine collection time in minutes)

Table of norms and interpretation of the received data

Stage chronic illness kidney	Description	GFR value (ml/min/1.73 sq.m.)	Recommendations
1	Kidney dysfunction with normal or increased GFR	≥90	Observation, diagnosis and elimination concomitant diseases, reducing the risk of developing complications from the cardiovascular system.
2	Impaired kidney function with a slight decrease in GFR	60-89	Research and elimination of kidney pathologies, predicting the development of complications
3	Average degree of GFR decline	30-59	Elimination of nephrological diseases, prevention of possible complications
4	Marked decrease in GFR	15-29	It is recommended to select a method and prepare for replacement therapy
5	Acute renal failure	≤15	Replacement therapy indicated

The kidney consists of a million units - nephrons, which are a glomerulus of blood vessels and tubules for the passage of fluid.

Nephrons remove waste products from the blood through urine. Up to 120 liters of liquid pass through them per day. Purified water is absorbed into the blood to carry out metabolic processes.

Harmful substances are eliminated from the body in the form of concentrated urine. From the capillary, under the pressure generated by the work of the heart, liquid plasma is pushed into the glomerular capsule. Protein and other large molecules remain in the capillaries.

If the kidneys are sick, nephrons die and new ones are not formed. The kidneys do not perform their cleansing mission well. From increased load healthy nephrons fail at an accelerated rate.

Methods to assess kidney function

To do this, the patient’s daily urine is collected and the creatinine content in the blood is calculated. Creatinine is a protein breakdown product. Comparison of indicators with reference values shows how well the kidneys cope with the function of cleansing the blood of waste products.

To find out the condition of the kidneys, another indicator is used - the glomerular filtration rate (GFR) of fluid through the nephrons, which in in good condition is 80-120 ml/min. With age metabolic processes GFR slows down too.

The fluid is filtered through a glomerular filter. It consists of capillaries, basement membrane and capsule.

Water and dissolved substances enter through the capillary indothelium, or more precisely, through its openings. The basement membrane prevents proteins from entering the kidney fluid. Filtration quickly wears out the membrane. Its cells are constantly renewed.

The purified liquid enters the capsule cavity through the basement membrane.

The sorption process is carried out due to the negative charge of the filter and pressure. Under pressure, fluid with the substances it contains moves from the blood into the glomerular capsule.

GFR is the main indicator of kidney function, and therefore their condition. It shows the volume of primary urine formation per unit of time.

Glomerular filtration rate depends on:

the amount of plasma penetrating the kidneys, the norm for this indicator is 600 ml per minute in healthy person average build;
filtration pressure;
filter surface area.

In normal conditions, GFR is at a constant level.

Calculation methods

Calculation of glomerular filtration rate is possible using several methods and formulas.

The determination process comes down to comparing the content of the control substance in the patient’s plasma and urine. The comparative standard is the fructose polysaccharide inulin.

GFR is calculated using the formula:

V urine is the volume of final urine.

Inulin clearance is a reference indicator when studying the content of other substances in primary urine. By comparing the release of other substances with inulin, the ways of their filtration from plasma are studied.

When conducting research in clinical settings creatinine is used. The clearance for this substance is called the Rehberg test.

To treat kidney diseases, our readers successfully use Galina Savina’s method.

Checking kidney function using the Cockcroft-Gault formula

In the morning, the patient drinks 0.5 liters of water and urinates in the toilet. Then every hour he collects the urine into separate containers. Moreover, it marks the time of the beginning and end of urination.

To calculate clearance, a certain amount of blood is taken from a vein. The formula calculates the creatinine content.

Formula: F1=(u1/p)v1.

Fi - CF;
U1 - content of control substance;
Vi – time of the first (studied) urination in minutes;
p - plasma creatinine content.

This formula is used to calculate the amount every hour. The calculation time is 24 hours.

Normal indicators

GFR shows the efficiency of nephrons and general state kidney

The normal glomerular filtration rate of the kidneys is 125 ml/min in men, and 11o ml/min in women.

In 24 hours, up to 180 liters of primary urine passes through the nephrons. In 30 minutes the entire volume of plasma is cleared. That is, in 1 day the blood is completely cleansed by the kidneys 60 times.

With age, the ability to intensively filter blood in the kidneys slows down.

Help in diagnosing diseases

GFR allows us to judge the state of the nephron glomeruli - the capillaries through which plasma enters for purification.

Direct measurement involves continuous injection of inulin into the blood to maintain its concentration. At this time, 4 portions of urine are taken at intervals of half an hour. Then calculations are made using the formula.

This method of measuring GFR is used for scientific purposes. It is too complex for clinical studies.

Indirect measurements are made by creatinine clearance. Its formation and removal are constant and are directly dependent on the volume of muscle mass in the body. In men leading active life, creatinine production is higher than in children and women.

This substance is mainly eliminated by glomerular filtration. But 5-10% of it passes through the proximal tubules. Therefore, there is some error in the indicators.

As filtration slows down, the content of the substance increases sharply. Compared to GFR, it is up to 70%. These are signs of kidney failure. The picture of the readings can be distorted by the content in the blood medicines.

Nevertheless, creatinine clearance is a more accessible and generally accepted analysis.

All daily urine is taken for research, with the exception of the first morning portion. The content of the substance in the urine in men should be 18-21 mg/kg, in women – 3 units less. Lower readings indicate kidney disease or improper urine collection.

The simplest way assessment of kidney function - determination of serum creatinine level. The higher this indicator, the lower the GFR. That is, the higher the filtration rate, the lower the creatinine content in the urine.

A glomerular filtration test is done if renal failure is suspected.

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What diseases can be identified?

GFR can help diagnose various shapes kidney diseases. If the filtration rate decreases, this may be a signal for the manifestation of a chronic form of insufficiency.

At the same time, the concentration of urea and creatinine in the urine increases. The kidneys do not have time to cleanse the blood from harmful substances.

In pyelonephritis, the nephron tubules are affected. The decrease in glomerular filtration rate occurs later. The Zimnitsky test will help determine this disease.

The amount of filtration increases in diabetes mellitus, hypertension, lupus erythematosus and some other diseases.

A decrease in GFR occurs when pathological changes, with massive loss of nephrons.

The reason may be a decrease blood pressure, shock, heart failure. Intracranial pressure rises with poor urine flow. Due to increased venous pressure in the kidney, the filtration process slows down.

How is research carried out in children?

To study GFR in children, the Schwartz formula is used.

The speed of blood flow in the kidneys is higher than in the brain and heart itself. This necessary condition filtration of blood plasma in the kidneys.

Reduced GFR can help diagnose incipient kidney disease in children. In clinical settings, the two most simple and sufficiently informative method measurements.

Progress of the study

In the morning, on an empty stomach, blood is taken from a vein to determine the level of creatinine in plasma. As already mentioned, it does not change during the day.

In the first case, two hour-long portions of urine are collected, noting the time of diuresis in minutes. By calculating using the formula, two GFR values are obtained.

The second option is to collect daily urine at intervals of 1 hour. You should get at least 1500 ml.

In a healthy adult, creatinine clearance is 100-120 ml per minute.

In children, a decrease to 15 ml per minute may be alarming. This indicates a decrease in kidney function, their painful condition. This does not always occur from the death of nephrons. It’s just that the filtration rate slows down in each particle.

The kidneys are the most important cleansing organ of our body. If their functioning is disrupted, many organs malfunction, the blood carries harmful substances, and partial poisoning of all tissues occurs.

Therefore, if you have the slightest concern in the kidney area, you should get tested, consult a doctor, undergo necessary examinations and start timely treatment.

1pochki.ru

GFR is a marker of kidney aging, CVD mortality and prostate cancer risk

To find out the condition of the kidneys, an indicator is used - the glomerular filtration rate (GFR) of fluid through the nephrons, which in the normal state is 80-120 ml/min. Glomerular filtration rate decreases with age. When it becomes too low, kidney failure occurs and the development of cardiovascular diseases and arterial calcification accelerates many times over. The risk of mortality increases sharply.

With age, metabolic processes slow down and so does GFR. GFR is the main indicator of kidney function, and therefore their condition. It shows the volume of primary urine formation per unit of time. Calculation of glomerular filtration rate is possible using several methods and formulas. The simplest is a calculation based on a blood test for creatinine (see in the picture).

Glomerular filtration rate (GFR) = (((140 - your age) x body weight in kg.) / blood creatinine in µmol/l) x (0.85 if the patient is a woman).

But even without determining GFR, simply by the value of creatinine in the blood you can approximately determine the condition of the kidneys.

So, when conducting research in clinical settings, creatinine is used. The clearance for this substance is called the Rehberg test. The simplest way to assess kidney function is to measure serum creatinine levels. The higher this indicator, the lower the GFR. The age of the kidneys can also be determined by creatinine (see table on the left - for men. For women, just below). That is, the higher the filtration rate, the lower the creatinine content in the urine, since it is filtered out more slowly. It is possible not to calculate the glomerular filtration rate during a cursory assessment of kidney function. A glomerular filtration test is done if renal failure is suspected.

In studies of people aged 65 to 89 years, it was shown that a decrease in glomerular filtration rate below 30 was associated with a strong increase in the risk of all-cause mortality.

www.ncbi.nlm.nih.gov/pubmed/24664801

But in very thin and elderly people, creatinine is not always a correct marker when it is much higher than the norm for determining GFR. And then another marker is used - Cystatin C. Cystatin C is an alternative to serum creatinine for assessing GFR, since cystatin C is less dependent on age and muscle mass.

www.ncbi.nlm.nih.gov/pubmed/24271191

But there are cases when cystatin C incorrectly indicates a change in kidney function. In 30% of people with diseases thyroid gland(its removal, partial removal, hypothyroidism, hyperthyroidism, etc.) cystatin C is incorrect. It is worth noting that cystatin C may be incorrect even with mild thyroid dysfunction.

www.ncbi.nlm.nih.gov/pubmed/15966508
www.ncbi.nlm.nih.gov/pubmed/14637271
www.ncbi.nlm.nih.gov/pubmed/12675875

In older populations with low CVD risk and normal kidney function, even small decreases in GFR are associated with an increased risk of all-cause and all-cause mortality. cardiovascular diseases(GCC)! And a recent meta-analysis showed that the glomerular filtration rate

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Glomerular filtration rate study

To measure the glomerular filtration rate (GFR), the clearance of substances is used that, during transport through the kidneys, are only filtered, without undergoing reabsorption or secretion in the tubules, are highly soluble in water, freely pass through the pores of the glomerular basement membrane and do not bind to plasma proteins. These substances include inulin, endogenous and exogenous creatinine, and urea. In recent years wide use received ethylenediaminetetraacetic acid and glomerulotropic radiopharmacological drugs, such as diethylenetriaminepentaacetate or iothalamate, labeled with radioisotopes as marker substances. They also began to use unlabeled contrast agents(unlabeled iothalamate and iohexol).

Glomerular filtration rate is the main indicator of kidney function in healthy and sick people. Its definition is used to assess the effectiveness of therapy aimed at preventing the progression of chronic diffuse kidney diseases.

Inulin, a polysaccharide with a molecular weight of 5200 daltons, can be considered an ideal marker for determining the glomerular filtration rate. It is freely filtered through the glomerular filter and is not secreted, reabsorbed or metabolized in the kidneys. In this regard, inulin clearance is used today as the “gold standard” for determining glomerular filtration rate. Unfortunately, there are technical difficulties in determining inulin clearance and it is an expensive study.

The use of radioisotope markers also makes it possible to determine the glomerular filtration rate. The results of the determinations closely correlate with inulin clearance. However, radioisotope research methods are associated with the introduction of radioactive substances, the presence of expensive equipment, as well as the need to comply with certain standards for the storage and administration of these substances. In this regard, studies of glomerular filtration rate using radioactive isotopes used in the presence of special radiological laboratories.

In recent years, GFR has been proposed as a marker new method using serum cystatin C, one of the protease inhibitors. Currently, due to the incompleteness of population studies in which the assessment is carried out this method, there is no information about its effectiveness.

Until recent years, endogenous creatinine clearance was the most widely used method for determining glomerular filtration rate in clinical practice. To determine the glomerular filtration rate, daily urine collection is carried out (for 1440 minutes) or urine is obtained at separate intervals (usually 2 intervals of 2 hours) with a preliminary water load to achieve sufficient diuresis. Endogenous creatinine clearance is calculated using the clearance formula.

A comparison of the GFR results obtained from the study of creatinine clearance and inulin clearance in healthy individuals revealed a close correlation of the indicators. However, with the development of moderate and, especially, severe renal GFR deficiency, calculated from endogenous creatinine clearance, significantly exceeded (by more than 25%) the GFR values obtained from inulin clearance. At a GFR of 20 ml/min, creatinine clearance exceeded inulin clearance by 1.7 times. The reason for the discrepancy in the results was that in conditions of renal failure and uremia, the kidney begins to secrete creatinine through the proximal tubules. Preliminary (2 hours before the start of the study) administration of cimetidine, a substance that blocks creatinine secretion, to the patient at a dose of 1200 mg helps to level out the error. After preliminary administration of cimetidine, creatinine clearance in patients with moderate and severe renal failure did not differ from inulin clearance.

Currently in clinical practice widely implemented calculation methods determination of GFR, taking into account the concentration of creatinine in the blood serum and a number of other indicators (gender, height, body weight, age). Cockroft and Gault proposed the following formula for calculating GFR, which is currently used by most medical practitioners.

Glomerular filtration rate for men is calculated using the formula:

(140 - age) x m: (72 x Rcr),

where Pcr is the concentration of creatinine in blood plasma, mg%; m - body weight, kg. GFR for women is calculated using the formula:

(140 - age) x m x 0.85: (72 x Rcr),

where Pcr is the concentration of creatinine in blood plasma, mg%; m - body weight, kg.

Comparison of GFR calculated using the Cockcroft-Gault formula with GFR values determined using the most accurate clearance methods (inulin clearance, 1125-iothalamate) revealed high comparability of the results. In the vast majority of comparative studies, the estimated GFR differed from the true one by 14% or less, and by 25% or less; in 75% of cases the differences did not exceed 30%.

In recent years, the MDRD (Modification of Diet in Renal Disease Study) formula has been widely introduced into practice to determine GFR:

GFR+6.09x(serum creatinine, mol/L)-0.999x(age)-0.176x(0.7b2 for women (1.18 for African Americans)x(serum urea, mol/L)-0.17x(albumin serum, g/l)0318.

Comparative studies showed the high reliability of this formula: in more than 90% of cases, the deviations of the calculation results using the MDRD formula did not exceed 30% of the measured GFR. Only in 2% of cases the error exceeded 50%.

Normally, the glomerular filtration rate for men is 97-137 ml/min, for women - 88-128 ml/min.

Under physiological conditions, the glomerular filtration rate increases during pregnancy and when eating food with high content protein and decreases as the body ages. Thus, after 40 years, the rate of decline in GFR is 1% per year, or 6.5 ml/min per decade. At the age of 60-80 years, GFR decreases by half.

With pathology, the glomerular filtration rate often decreases, but can also increase. In diseases not associated with kidney pathology, a decrease in GFR is most often caused by hemodynamic factors - hypotension, shock, hypovolemia, severe heart failure, dehydration, and NSAID use.

In kidney diseases, a decrease in the filtration function of the kidneys is mainly due to structural disorders, which lead to a decrease in the mass of active nephrons, a decrease in the filtering surface of the glomerulus, a decrease in the ultrafiltration coefficient, a decrease in renal blood flow, and obstruction of the renal tubules.

These factors cause a decrease in the glomerular filtration rate in all chronic diffuse kidney diseases [chronic glomerulonephritis (CGN), pyelonephritis, polycystic kidney disease, etc.], kidney damage within systemic diseases connective tissue, with the development of nephrosclerosis against the background of arterial hypertension, acute renal failure, obstruction of the urinary tract, severe damage to the heart, liver and other organs.

In pathological processes in the kidneys, it is much less common to detect an increase in GFR due to an increase in ultrafiltration pressure, ultrafiltration coefficient, or renal blood flow. These factors are important in the development of high GFR in early stages diabetes mellitus, hypertension, systemic lupus erythematosus, in initial period formation of nephrotic syndrome. Currently, long-term hyperfiltration is considered as one of the non-immune mechanisms of progression of renal failure.

ilive.com.ua

Glomerular filtration of the kidneys

Glomerular filtration of the kidneys is a process as a result of which water and some substances dissolved in it are passively released from the blood into the lumen of the nephron capsule through the renal membrane. This process, along with others (secretion, reabsorption), is part of the mechanism of urine formation.

Measuring glomerular filtration rate is of great clinical importance. It, although indirectly, quite accurately reflects the structural and functional characteristics of the kidneys, namely, the number of functioning nephrons and the state of the renal membrane.

Nephron structure

Urine is a concentrate of substances, the removal of which from the body is necessary to maintain constancy internal environment. This is a kind of “waste” from life, including toxic ones, the further transformation of which is impossible, and the accumulation is harmful. The function of removing these substances is performed by the urinary system, the main part of which is the kidneys - biological filters. Blood passes through them, freeing itself from excess fluid and toxins.

Nephron is component kidneys, thanks to which it performs its function. Normally, the kidney has about 1 million nephrons, and each produces a certain amount of urine. All nephrons are connected by tubules through which urine is collected in the pyelocaliceal system and removed from the body through the urinary tract.

In Fig. Figure 1 schematically shows the structure of the nephron. A – renal corpuscle: 1 – afferent artery; 2– efferent artery; 3 – epithelial layers of the capsule (external and internal); 4 – beginning of the nephron tubule; 5 – vascular glomerulus. B – nephron itself: 1 – glomerular capsule; 2 – nephron tubule; 3 – collecting duct. Blood vessels of the nephron: a – afferent artery; b – efferent artery; c – tubular capillaries; d – nephron vein.

Rice. 1

In various pathological processes, reversible or irreversible damage to the nephrons occurs, as a result of which some of them may cease to perform their functions. The result is a change in urine production (retention of toxins and water, loss of useful substances through kidney and other syndromes).

The concept of glomerular filtration

The process of urine formation consists of several stages. At each stage, a failure may occur, leading to dysfunction of the entire organ. The first stage of urine formation is called glomerular filtration.

Why do humans need kidneys?

It is carried out by the renal corpuscle. It consists of a network of small arteries formed in the form of a glomerulus surrounded by a two-layer capsule. The inner layer of the capsule fits tightly to the walls of the arteries, forming a renal membrane (glomerular filter, from the Latin glomerulus - glomerulus).

It consists of the following elements:

endothelial cells (the inner “lining” of arteries);
epithelial capsule cells forming its inner layer;
layer of connective tissue (basal membrane).

It is through the renal membrane that water is released and various substances, and how fully the kidneys perform their function depends on its condition.

Through the renal membrane, water is passively filtered from the blood along a pressure gradient, and along with it, substances with small molecular sizes are released along an osmotic gradient. This process is glomerular filtration.

Large (protein) molecules and cellular elements of the blood do not pass through the kidney membrane. In some diseases, they can still pass through it due to its increased permeability and end up in the urine.

The solution of ions and small molecules in the filtered liquid is called primary urine. The content of substances in its composition is very low. It is similar to plasma from which the protein has been removed. The kidneys filter from 150 to 190 liters of primary urine in one day. During the further transformation that primary urine undergoes in the nephron tubules, its final volume decreases by approximately 100 times, to 1.5 liters (secondary urine).

Due to the fact that during passive tubular filtration it enters the primary urine a large number of water and needed by the body substances, removing it from the body unchanged would be biologically impractical. In addition, some toxic substances are formed in quite large quantities, and their elimination should be more intense. Therefore, primary urine, passing through the tubular system, undergoes transformation through secretion and reabsorption.

In Fig. Figure 2 shows diagrams of tubular reabsorption and secretion.

Rice. 2

Tubular reabsorption (1). This is the process by which water, as well as necessary substances through the work of enzyme systems, mechanisms of ion exchange and endocytosis, it is “taken” from primary urine and returned to the bloodstream. This is possible due to the fact that the nephron tubules are densely entwined with capillaries.

Tubular secretion (2) is the reverse process of reabsorption. This is the removal of various substances using special mechanisms. Epithelial cells actively, contrary to the osmotic gradient, they “remove” some substances from the vascular bed and secrete them into the lumen of the tubules.

As a result of these processes, there is an increase in the concentration of harmful substances in the urine, the elimination of which is necessary, compared to their concentration in the plasma (for example, ammonia, metabolites medicinal substances). It also prevents the loss of water and nutrients (for example, glucose).

This ratio of filtration mechanisms, as well as secretion and reabsorption, determines the volume of excretion (release) of certain substances along with urine.

Some substances are indifferent to the processes of secretion and reabsorption; their content in the urine is proportional to that in the blood (one example is insulin). Correlating the concentration of such a substance in urine and blood allows us to draw a conclusion about how well or poorly glomerular filtration occurs.

Glomerular filtration rate (GFR) is an indicator that is the main quantitative reflection of the process of formation of primary urine. In order to understand what changes reflect fluctuations in this indicator, it is important to know what GFR depends on.

It is influenced by the following factors:

The volume of blood passing through the vessels of the kidneys in a certain time period.
Filtration pressure is the difference between the pressure in the arteries of the kidney and the pressure of filtered primary urine in the capsule and tubules of the nephron.
Filtration surface is the total area of capillaries that participate in filtration.
Number of functioning nephrons.

You can calculate the glomerular filtration rate using the formulas

The first 3 factors are relatively variable and are regulated through local and general neurohumoral mechanisms. The last factor - the number of functioning nephrons - is quite constant, and it is this factor that most strongly influences the change (decrease) in glomerular filtration rate. Therefore, in clinical practice, GFR is most often studied to determine the stage of chronic renal failure (it develops precisely due to the loss of nephrons due to various pathological processes).

GFR is most often determined by a calculation method based on the ratio of the content in the blood and urine of a substance that is always present in the body - creatinine.

This test is also called endogenous creatinine clearance (Rehberg test). There are special formulas for calculating GFR; they can be used in calculators and computer programs. The calculation is not particularly difficult. IN normal GFR is:

75–115 ml/min in women;
95–145 ml/min in men.

Determination of glomerular filtration rate is the method most commonly used to assess kidney function and the stage of renal failure. Based on the results of this analysis (including), a prognosis of the course of the disease is made, treatment regimens are developed, and the issue of transferring the patient to dialysis is decided.

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Factors that change the kidney's glomerular filtration rate

Glomerular filtration rate is determined by several factors:

The rate of plasma flow in the kidneys is the amount of blood that flows per unit time through the afferent arteriole in the glomerulus. Normal indicator, if a person is healthy, is 600 ml/min (calculation based on data on an average person weighing 70 kg).
Pressure level in blood vessels. Normally, when the body is healthy, the pressure in the afferent vessel is higher than in the efferent vessel. Otherwise, the filtration process does not occur.
Number of functional nephrons. There are pathologies that affect the cellular structure of the kidney, as a result of which the number of capable nephrons is reduced. Such a violation subsequently causes a reduction in the filtration surface area, the size of which directly affects the GFR.

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Reberg-Tareev test

The Reberg-Tareev test examines the level of clearance of creatinine produced by the body - the volume of blood from which it is possible to filter 1 mg of creatinine by the kidneys in 1 minute. The amount of creatinine can be measured in clotted plasma and urine. The validity of a study depends on the time at which the analysis was collected. The study is often carried out like this: urine is collected for 2 hours. It measures creatinine levels and minute diuresis (the volume of urine produced per minute). GFR is calculated based on the obtained values of these two indicators. Less commonly used are 24-hour urine collection and 6-hour samples. Regardless of what technique the doctor uses, the patient’s blood is taken from a vein the next morning, before he has had breakfast, to conduct a creatinine clearance test.

A creatinine clearance test is prescribed in the following cases:

pain in the kidney area, swelling of the eyelids and ankles;
impaired urination, dark-colored urine with blood;
you need to install the right dose medicines for the treatment of kidney diseases;
diabetes type 1 and 2;
hypertension;
abdominal obesity, insulin resistance syndrome;
smoking abuse;
cardiovascular diseases;
before surgery;
chronic kidney disease.

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Cockcroft-Gold test

The Cockcroft-Gold test also determines the concentration of creatinine in the blood serum, but differs from the method described above for collecting materials for analysis. The test is carried out as follows: in the morning on an empty stomach, the patient drinks 1.5-2 glasses of liquid (water, tea) to activate urine production. After 15 minutes the patient passes little need into the toilet to clean bladder from the remains of formations during sleep. Next comes peace. An hour later, the first urine sample is taken and its time is recorded. The second portion is collected in the next hour. Between this, 6-8 ml of blood is taken from the patient from a vein. Next, based on the results obtained, the creatinine clearance and the amount of urine that is formed per minute are determined.

Glomerular filtration rate according to MDRD formula

This formula takes into account the gender and age of the patient, so with its help it is very easy to observe how the kidneys change with age. It is very often used to diagnose renal dysfunction in pregnant women. The formula itself looks like this: GFR = 11.33 * Crk - 1.154 * age - 0.203 * K, where Crk is the amount of creatinine in the blood (mmol/l), K is a coefficient depending on gender (in women - 0.742). If this indicator is given in micromoles (µmol/l) at the conclusion of the analysis, then its value must be divided by 1000. Main disadvantage This calculation method gives incorrect results with increased CF.

Reasons for the decrease and increase in the indicator

Exist physiological reasons changes in GFR. During pregnancy, the level increases, and when the body ages, it decreases. Food with high content squirrel. If a person has a pathology of renal function, then CF can either increase or decrease, it all depends on the specific disease. GFR is the earliest indicator of renal dysfunction. The intensity of CF decreases much faster than the ability of the kidneys to concentrate urine is lost and nitrogenous waste accumulates in the blood.

When the kidneys are sick, reduced blood filtration in the kidneys is provoked by disturbances in the structure of the organ: the number of active structural units of the kidney, the ultrafiltration coefficient decreases, changes occur in the renal blood flow, the filtering surface decreases, and obstruction of the kidney tubules occurs. It is caused by chronic diffuse, systemic kidney diseases, nephrosclerosis against the background of arterial hypertension, acute liver failure, severe heart and liver diseases. In addition to kidney disease, extrarenal factors influence GFR. A decrease in speed is observed together with cardiac and vascular failure, after an attack severe diarrhea and vomiting, with hypothyroidism, prostate cancer.

An increase in GFR is a rarer phenomenon, but manifests itself in early stages of diabetes mellitus, hypertension, systemic development of lupus erythematosus, and at the beginning of the development of nephrotic syndrome. Medicines that affect creatinine levels (cephalosporin and similar effects on the body) can also increase the rate of CF. The medicine increases its concentration in the blood, so when taking a test, falsely elevated results are detected.

Load tests

Load tests are based on the ability of the kidneys to accelerate glomerular filtration under the influence of certain substances. With the help of such a study, the CF reserve or renal functional reserve (RFR) is determined. To recognize it, a one-time (acute) load of protein or amino acids is applied, or they are replaced with a small amount of dopamine.

Protein loading involves changing your diet. You need to consume 70−90 grams of protein from meat (1.5 grams of protein per 1 kilogram of body weight), 100 grams of protein plant origin or administer an amino acid set intravenously. People without health problems experience an increase in GFR by 20−65% within 1−2.5 hours after receiving a dose of protein. The average PFR value is 20−35 ml per minute. If there is no increase, then most likely the person’s renal filter permeability is impaired or vascular pathologies develop.

The Importance of Research

It is important to monitor GFR for people with the following conditions:

chronic and acute course glomerulonephritis, as well as its secondary appearance;
renal failure;
inflammatory processes provoked by bacteria;
kidney damage due to systemic lupus erythematosus;
nephrotic syndrome;
glomerulosclerosis;
renal amyloidosis;
nephropathy in diabetes, etc.

These diseases cause a decrease in GFR long before any symptoms appear. functional disorders kidneys, increased levels of creatinine and urea in the patient’s blood. In an advanced state, the disease provokes the need for a kidney transplant. Therefore, in order to prevent the development of any kidney pathologies, it is necessary to regularly conduct studies of their condition.

Glomerular filtration rate is one of the main indicators of kidney health. On initial stage of its formation, urine is filtered as a liquid contained in the blood plasma into the renal glomerulus, through the small vessels into the capsule cavity. This happens in the following way:

Kidney capillaries are lined from the inside flat epithelium, between the cells of which there are tiny holes, the diameter of which does not exceed 100 nanometers. Blood cells cannot pass through them, they are too large for this, while the water contained in the plasma and the substances dissolved in it pass freely through this filter,

the next stage is the basement membrane located inside the renal glomerulus. Its pore size is no more than 3 nm, and the surface is negatively charged. The main task of the basement membrane is to separate protein formations present in the blood plasma from the primary urine. Complete renewal of basement membrane cells occurs at least once a year,

and finally, the primary urine reaches the podocytes - processes of the epithelium lining the glomerulus capsule. The size of the pores that are located between them is about 10 nm, and the myofibrils present here act as a pump, redirecting primary urine into the glomerular capsule.

The glomerular filtration rate, which is the main quantitative characteristic of this process, refers to the volume of initial urine formed in the kidneys in 1 minute.

Normal glomerular filtration rate. Explanation of the result (table)

Glomerular filtration rate depends on the age and gender of a person. It is usually measured as follows: after the patient wakes up in the morning, he is given approximately 2 glasses of water to drink. After 15 minutes, he urinates normally, marking the time when urination ends. The patient goes to bed and exactly an hour after finishing urination, he urinates again, collecting urine. Half an hour after the end of urination, blood is drawn from a vein - 6-8 ml. An hour after urination, the patient urinates again and again collects a portion of urine in a separate container. The glomerular filtration rate is determined by the volume of urine collected in each portion and by the clearance of endogenous creatinine in the serum and in the collected urine.

In a normal, healthy, middle-aged person, the normal GFR is:

in men – 85-140 ml/min,
in women - 75-128 ml/min.

Then the glomerular filtration rate begins to decrease - over 10 years by approximately 6.5 ml/min.

Glomerular filtration rate is determined if there is a suspicion of whole line kidney diseases - it is this that allows you to quickly identify the problem even before the level of urea and creatinine in the blood increases.

The initial stage of chronic renal failure is considered to be a decrease in glomerular filtration rate to 60 ml/min. Renal failure can be compensated - 50-30 ml/min and decompensated when GFR drops to 15 ml/min and below. Intermediate GFR values are called subcompensated renal failure.

If the glomerular filtration rate decreases significantly, then additional examination of the patient is required to find out whether he has kidney damage. If the examination results show nothing, the patient is diagnosed with a decrease in glomerular filtration rate.

Glomerular filtration rate is normal for ordinary people and for pregnant women:

If the glomerular filtration rate is increased, what does this mean?

If the glomerular filtration rate differs from the norm in the direction of increase, this may indicate the development of the following diseases in the patient’s body:

systemic lupus erythematosus,
hypertension,
nephrotic syndrome,
diabetes.

If the glomerular filtration rate is calculated by creatinine clearance, then you need to remember that taking certain medications can lead to an increase in its concentration in blood tests.

If the glomerular filtration rate is reduced, what does this mean?

The following pathologies can lead to a decrease in the glomerular filtration rate:

cardiovascular failure,
dehydration due to vomiting and diarrhea,
decreased thyroid function,
liver diseases,
acute and chronic glomerulonephritis,
tumors prostate gland in men.

A sustained decrease in glomerular filtration rate to 40 ml/min is usually called severe renal failure; a decrease to 5 ml/min or less is the end stage of chronic renal failure.

Glomerular filtration rate (GFR) is a sensitive indicator of the functional state of the kidneys; its decrease is considered one of early symptoms renal dysfunction. A decrease in GFR, as a rule, occurs much earlier than a decrease in the concentration function of the kidneys and the accumulation of nitrogenous waste in the blood. In case of primary glomerular lesions, insufficiency of the concentrating function of the kidneys is detected when sharp decline GFR (approximately 40-50%). At chronic pyelonephritis The distal part of the tubules is predominantly affected, and filtration decreases later than the concentration function of the tubules. Impaired renal concentration function and sometimes even slight increase the content of nitrogenous wastes in the blood in patients with chronic pyelonephritis is possible in the absence of a decrease in GFR.

GFR is influenced by extrarenal factors. Thus, GFR decreases in cardiac and vascular insufficiency, profuse diarrhea and vomiting, hypothyroidism, mechanical obstruction of urine outflow (prostate tumors), liver damage. IN initial stage acute glomerulonephritis a decrease in GFR occurs not only due to impaired patency of the glomerular membrane, but also as a result of hemodynamic disorders. In chronic glomerulonephritis, a decrease in GFR may be due to azotemic vomiting and diarrhea.

A persistent drop in GFR to 40 ml/min in chronic renal pathology indicates severe renal failure, a drop to 15-5 ml/min indicates the development of terminal chronic renal failure.

Some drugs (for example, cimetidine, trimethoprim) reduce tubular secretion of creatinine, increasing its concentration in the blood serum. Antibiotics of the cephalosporin group, due to interference, lead to falsely elevated results in determining creatinine concentration.

Laboratory criteria for the stages of chronic renal failure

Blood creatinine, mmol/l

GFR, % of predicted

An increase in GFR is observed in chronic glomerulonephritis with nephrotic syndrome, in the early stages of hypertension. It should be remembered that in nephrotic syndrome, the clearance of endogenous creatinine does not always correspond to the true state of GFR. This is due to the fact that in nephrotic syndrome, creatinine is secreted not only by the glomeruli, but also secreted by the altered tubular epithelium, and therefore to very good. endogenous creatinine can be up to 30% higher than the true volume of glomerular filtrate.

The clearance of endogenous creatinine is influenced by the secretion of creatinine by renal tubular cells, so its clearance may significantly exceed the true value of GFR, especially in patients with kidney disease. To obtain accurate results, it is extremely important to completely collect urine within a precisely specified period of time; incorrect collection of urine will lead to false results.

In some cases, to improve the accuracy of determining endogenous creatinine clearance, H2 antagonists are prescribed -histamine receptors(usually cimetidine at a dose of 1200 mg 2 hours before the start of 24-hour urine collection), which block tubular secretion of creatinine. Endogenous creatinine clearance measured after taking cimetidine is almost equal to the true GFR (even in patients with moderate to severe renal impairment).

To do this, it is necessary to know the patient’s body weight (kg), age (years) and serum creatinine concentration (mg%). Initially, a straight line connects the patient’s age and his body weight and marks a point on line A. Then mark the concentration of creatinine in the blood serum on the scale and connect it with a straight line to a point on line A, continuing it until it intersects with the endogenous creatinine clearance scale. The point of intersection of the straight line with the endogenous creatinine clearance scale corresponds to GFR.

Tubular reabsorption. Tubular reabsorption (CR) is calculated from the difference between glomerular filtration and minute diuresis (D) and is calculated as a percentage of glomerular filtration using the formula: CR = [(GFR-D)/GFR]×100. Normal tubular reabsorption ranges from 95 to 99% of the glomerular filtrate.

Tubular reabsorption can vary significantly under physiological conditions, decreasing by up to 90% with water loading. A marked decrease in reabsorption occurs with forced diuresis caused by diuretics. The greatest decrease in tubular reabsorption is observed in patients diabetes insipidus. A persistent decrease in water reabsorption below 97-95% is observed with primary and secondary wrinkled kidneys and chronic pyelonephritis. Water reabsorption may also decrease with acute pyelonephritis. In pyelonephritis, reabsorption decreases before the GFR decreases. In glomerulonephritis, reabsorption decreases later than GFR. Usually, along with a decrease in water reabsorption, insufficiency of the concentration function of the kidneys is detected. In this regard, a decrease in water reabsorption in functional diagnostics large kidney clinical significance does not have.

An increase in tubular reabsorption is possible with nephritis and nephrotic syndrome.

Every day, 70-75% of all fluid consumed during the day is excreted from the human body. This work is done by the kidneys. The functioning of this system depends on factors, one of which remains glomerular filtration.

Reasons for the decline

Glomerular filtration is a process of processing blood entering the kidneys that occurs in the nephrons. The blood is purified 60 times per day. Normal blood pressure is 20 mm Hg. The filtration rate depends on the area occupied by the nephron capillaries, pressure and membrane permeability.

When glomerular filtration is impaired, two processes can occur: a decrease and an increase in function.

A decrease in glomerular activity can be caused by factors both related to the kidneys and extrarenal:

hypotension;
narrowed renal artery;
high oncotic pressure;
membrane damage;
decrease in the number of glomeruli;
impaired urinary outflow.

Factors that stimulate the development of glomerular filtration disorders cause further development diseases:

a decrease in pressure occurs when stressful conditions, with pronounced pain syndrome, leads to cardiac decompensation;
narrowing of the arteries leads to hypertension, lack of urine with severe pain;
anuria leads to a complete cessation of filtration.

The reduction in glomerular area may be due to inflammatory processes, sclerosis of blood vessels.

With hypertension and cardiac decompensation, the permeability of the membrane increases, but filtration is reduced: some of the glomeruli are switched off from performing their function.

If glomerular permeability is increased, protein yield may increase. This causes proteinuria.

Increased filtration

Impairment of glomerular filtration can be observed both in a decrease and in an increase in the growth rate. This dysfunction is unsafe. The reasons may be:

reduced oncotic pressure;
changes in pressure in the outgoing and incoming arterioles.

Such spasms can be observed in diseases:

nephritis;
hypertension;
administration of a small dose of adrenaline;
impaired blood circulation in peripheral vessels;
blood thinning;
copious introduction of fluid into the body.

Any abnormalities associated with glomerular filtration should be under the attention of a physician. An analysis to identify them is usually prescribed for existing suspicions of kidney disease, heart disease and other pathologies that indirectly lead to renal dysfunction.

How to determine?

A test is prescribed to determine the rate of filtration in the kidneys. It consists in determining the clearance rate, i.e. substances that are filtered in the blood plasma and do not undergo reabsorption or secretion. One of these substances is creatinine.

Normal glomerular filtration rate is 120 ml per minute. However, fluctuations in the range from 80 to 180 ml per minute are acceptable. If the volume goes beyond these limits, you need to look for the reason.

Previously, other tests were carried out in medicine to determine disorders of glomerular functioning. The basis was taken on substances that were administered intravenously. It takes several hours to observe how they are filtered. Blood plasma was taken for research, and the concentration of administered substances was determined. But this process is difficult, so today they resort to a simplified version of tests that measure creatinine levels.

Treatment of kidney filtration disorders

Impaired glomerular filtration is not independent disease, so it is not subject to targeted treatment. This is a symptom or consequence of damage to the kidneys or other internal organs already present in the body.

A decrease in glomerular filtration occurs in diseases:

heart failure;
tumors that reduce pressure in the kidney;
hypotension.

An increase in glomerular filtration rate occurs due to:

nephrotic syndrome;
lupus erythematosus;
hypertension;
diabetes mellitus

I have these diseases different nature, so their treatment is selected after thorough examination patient. Pass the comprehensive diagnostics and treatment according to your profile is possible in the German clinic Friedrichshafen. Here the patient will find everything he needs: polite staff, medical equipment, attentive service from nurses.

In case of illness, correction of the condition is possible, against the background of which the activity of the kidneys also improves. In diabetes mellitus, normalizing nutrition and administering insulin can improve the patient's condition.

If glomerular filtration is impaired, you need to follow a diet. Food should not be fatty, fried, salty or spicy. It is recommended to maintain an increased drinking regime. Protein intake is limited. It is better to cook food by steaming, boiling or stewing. Compliance with the diet is prescribed during treatment and after it for prevention.

These measures to prevent and improve kidney function will help cope with other concomitant diseases.

In contact with

To measure the glomerular filtration rate (GFR), the clearance of substances is used that, during transport through the kidneys, are only filtered, without undergoing reabsorption or secretion in the tubules, are highly soluble in water, freely pass through the pores of the glomerular basement membrane and do not bind to plasma proteins. These substances include inulin, endogenous and exogenous creatinine, and urea. In recent years, ethylenediaminetetraacetic acid and glomerulotropic radiopharmacological drugs, such as diethylenetriaminepentaacetate or iothalamate, labeled with radioisotopes, have become widespread as marker substances. Unlabeled contrast agents (unlabeled iothalamate and iohexol) were also used.

The use of radioisotope markers also makes it possible to determine the glomerular filtration rate. The results of the determinations closely correlate with inulin clearance. However, radioisotope research methods are associated with the introduction of radioactive substances, the presence of expensive equipment, as well as the need to comply with certain standards for the storage and administration of these substances. In this regard, studies of glomerular filtration rate using radioactive isotopes are used in the presence of special radiological laboratories.

In recent years, a new method using serum cystatin C, one of the protease inhibitors, has been proposed as a marker of GFR. Currently, due to the incompleteness of population studies evaluating this method, there is no information about its effectiveness.

A comparison of the GFR results obtained from the study of creatinine clearance and inulin clearance in healthy individuals revealed a close correlation of the indicators. However, with the development of moderate and, especially, severe renal failure, GFR, calculated from the clearance of endogenous creatinine, significantly exceeded (by more than 25%) the GFR values obtained from inulin clearance. At a GFR of 20 ml/min, creatinine clearance exceeded inulin clearance by 1.7 times. The reason for the discrepancy in the results was that in conditions of renal failure and uremia, the kidney begins to secrete creatinine through the proximal tubules. Preliminary (2 hours before the start of the study) administration of cimetidine, a substance that blocks creatinine secretion, to the patient at a dose of 1200 mg helps to level out the error. After preliminary administration of cimetidine, creatinine clearance in patients with moderate and severe renal failure did not differ from inulin clearance.

Currently, calculation methods for determining GFR have been widely introduced into clinical practice, taking into account the concentration of creatinine in the blood serum and a number of other indicators (gender, height, body weight, age). Cockroft and Gault proposed the following formula for calculating GFR, which is currently used by most medical practitioners.

Glomerular filtration rate for men is calculated using the formula:

(140 - age) x m: (72 x R cr),

where P cr is the concentration of creatinine in the blood plasma, mg%; m - body weight, kg. GFR for women is calculated using the formula:

(140 - age) x m x 0.85: (72 x R cr),

where P cr is the concentration of creatinine in the blood plasma, mg%; m - body weight, kg.

Comparison of GFR calculated using the Cockcroft-Goult formula with GFR values determined using the most accurate clearance methods (inulin clearance, 1,125-iothalamate) revealed high comparability of the results. In the vast majority of comparative studies, the estimated GFR differed from the true one by 14% or less, and by 25% or less; in 75% of cases the differences did not exceed 30%.

In recent years, the MDRD (Modification of Diet in Renal Disease Study) formula has been widely introduced into practice to determine GFR:

GFR+6.09 x (serum creatinine, mol/L) -0.999 x (age) -0.176 x (0.7b2 for women (1.18 for African Americans) x (serum urea, mol/L) -0.17 x ( serum albumin, g/l) 0318.

Comparative studies have shown the high reliability of this formula: in more than 90% of cases, deviations in the results of calculations using the MDRD formula did not exceed 30% of the measured GFR. Only in 2% of cases the error exceeded 50%.

Normally, the glomerular filtration rate for men is 97-137 ml/min, for women - 88-128 ml/min.

Under physiological conditions, the glomerular filtration rate increases during pregnancy and when consuming foods high in protein and decreases as the body ages. Thus, after 40 years, the rate of decline in GFR is 1% per year, or 6.5 ml/min per decade. At the age of 60-80 years, GFR decreases by half.

In kidney diseases, a decrease in the filtration function of the kidneys is associated mainly with structural disorders that lead to a decrease in the mass of active nephrons, a decrease in the filtering surface of the glomerulus, a decrease in the ultrafiltration coefficient, a decrease in renal blood flow, and obstruction of the renal tubules.

These factors cause a decrease in the glomerular filtration rate in all chronic diffuse kidney diseases [chronic glomerulonephritis (CGN), pyelonephritis, polycystic kidney disease, etc.], kidney damage as part of systemic connective tissue diseases, with the development of nephrosclerosis against the background of arterial hypertension, acute renal failure , obstruction of the urinary tract, severe damage to the heart, liver and other organs.

In pathological processes in the kidneys, it is much less common to detect an increase in GFR due to an increase in ultrafiltration pressure, ultrafiltration coefficient, or renal blood flow. These factors are important in the development of high GFR in the early stages of diabetes mellitus, hypertension, systemic lupus erythematosus, and in the initial period of the formation of nephrotic syndrome. Currently, long-term hyperfiltration is considered as one of the non-immune mechanisms of progression of renal failure.