GFR glomerular filtration rate. Normal glomerular filtration rate in adults and children

Description

Determination method

calculation using the CKD-EPI-creatinine formula (calibrator for creatinine, traceable to the IDMS method).

Material under study Blood serum

Determining the glomerular filtration rate is of utmost importance for diagnosis, determining the stage of the disease, assessing the prognosis, choosing treatment tactics, and deciding on the initiation of replacement therapy for chronic kidney diseases. However, at present there is no accessible, easy-to-use and at the same time maximum exact method estimates of glomerular filtration.

The reference methods are clearance methods using the introduction of exogenous substances that have the necessary ideal characteristics(excreted from the blood only by glomerular filtration, without being reabsorbed or secreted in the renal tubules). These include methods for assessing filtration by the rate of excretion of inulin, 51Cr-EDTA, 125I-iothalamate or iohexol. Limits wide application such methods, their complexity, high price, the need for intravenous administration of substances foreign to the body. Does not require intravenous injections of the test substance, a method for assessing glomerular filtration by the clearance of endogenous creatinine (see test, Reberg-Tareev test). Creatinine is formed in muscles and is excreted from the blood in normal conditions mainly by glomerular filtration, without being reabsorbed or secreted in the renal tubules.

Assessing filtration based on the ratio of creatinine concentration in the blood and its excretion in urine, taking into account body size (normalization to a standard body surface), gender and age of the patient (separate reference values) in most situations allows one to assess changes in filtration level with satisfactory accuracy, so this method has Wide application.

The method gives somewhat distorted results on late stages renal failure, because at very high concentrations in the blood, creatinine begins to be secreted in the renal tubules. In addition, the Reberg-Tareev test is not convenient enough and is not always acceptable for the patient, since it involves collecting urine excreted during the day. Failure to comply with the rules for collecting urine often leads to an erroneous result.

As a result of the search for more convenient methods, screening methods for calculating the glomerular filtration rate in the kidneys based on the level of blood creatinine (eGFR, estimated Glomerular Filtration Rate) were developed and put into practice using formulas based only on measuring blood creatinine and knowledge of the patient’s gender, age and ethnicity . They were bred by statistical analysis and comparison of creatinine measurements and glomerular filtration rate estimates using clearance methods in a large number of patients of different ages and gender with chronic kidney pathology.

One of the most common options for calculating glomerular filtration rate is the MDRD formula (obtained in the Modification of Diet in Renal Disease clinical study). The calculation result takes into account gender, age and is normalized relative to the conditional average human body surface of 1.73 m2, which allows it to be used to gradate the level of glomerular filtration and classify the stage of chronic kidney disease. Result<60 мл/мин/1,73 м2 интерпретируется как снижение фильтрации. Существенный недостаток формулы MDRD – неточные (заниженные) результаты на уровне истинной скорости фильтрации >60 ml/min/1.73 m2.

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formula, subsequently developed by the same group of researchers, increases the accuracy of calculations in the range of 60–90 ml/min/1.73 m2 and is currently recommended for use as the most suitable in outpatient and clinical practice screening method for assessing glomerular filtration rate (KDIGO, 2013, National recommendations: chronic illness kidney, 2012). The CKD-EPI formula assumes that the method used to measure the patient's blood creatinine level is comparable to the method on which the formula was developed (the calibration material is standardized to the reference method of Isotope Dilution Mass Spectrometry, IDMS).

Calculation of glomerular filtration rate based on blood creatinine level is focused on the conditional “average” patient and is less accurate than assessing glomerular filtration using clearance methods.

It is unacceptable in the following situations:

the patient's body size and muscle mass deviate sharply from the average (bodybuilders, patients with limb amputations);
severe wasting and obesity (BMI<15 и >40 kg/m2);
pregnancy;
diseases of skeletal muscles (myodystrophy);
paralysis/paresis of limbs;
vegetarian diet;
rapid decline in kidney function (acute or rapidly progressive nephritic syndrome);
laboratory tests to resolve the issue of dosage of nephrotoxic drugs;
making a decision to initiate renal replacement therapy;
condition after kidney transplant.

In these cases, one should resort to more accurate clearance methods for assessing the level of glomerular filtration.

Literature

National recommendations. Chronic kidney disease: basic principles of screening, diagnosis, prevention and treatment approaches. Clinical Nephrology No. 4, 2012, p. 4-26.
KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease/ – Kidney Int/ 2013, Vol 3 Issue 1.
Stevens L.A., Claybon M.A., Schmid C.H. et al. Evaluation of the Chronic Kidney Disease Epidemiology Collaboration equation for estimating the glomerular filtration rate in multiple ethnicities. Kidney Int. 2011; 79:555–562.

Preparation

It is preferable to take blood in the morning on an empty stomach, after 8-14 hours of overnight fasting (you can drink water), it is acceptable in the afternoon 4 hours after easy reception food. On the eve of the study, it is necessary to exclude increased psycho-emotional and physical stress ( sports training), drinking alcohol.

Indications for use

Screening assessment of renal function (for limitations, see Description section).

Interpretation of results

Interpretation of research results contains information for the attending physician and is not a diagnosis. The information in this section cannot be used for self-diagnosis and self-treatment. Accurate diagnosis is determined by the doctor, using both the results of this examination and the necessary information from other sources: medical history, results of other examinations, etc.

Calculation formulas for patients (Caucasians), where CREAT is serum creatinine, µmol/l:

Women - if blood creatinine is lower than or equal to 62 µmol/l: CKD-EPI = 144 × (0.993^YEARS) × ((CREAT/88.4)/0.7)^(−0.328))

Women - if blood creatinine is above 62 µmol/l: CKD-EPI = 144 × (0.993^YEARS) × ((CREAT/88.4)/0.7)^(−1.210))

Men - if blood creatinine is less than or equal to 80 µmol/l: CKD-EPI = 141 × (0.993^YEARS) × ((CREAT/88.4)/0.9)^(−0.412))

Men - if blood creatinine is above 80 µmol/l: CKD-EPI = 141 × (0.993^YEARS) × ((CREAT/88.4)/0.9)^(−1.210))

Note. The original CKD-EPI formula, derived primarily from Caucasian patients, is used. When assessing the influence of race/ethnicity using patients from the United States, Europe, China, Japan, and South Africa The following racial/ethnic adjustment factors were developed: African Americans - x1.16, Asians - x1.05 (women) and x1.06 (men), American Indians and Hispanics - x1.01 (compared to the rest of the mixed group).

The use of such modified equations for four racial-ethnic groups showed satisfactory results when validated in the USA, Europe, and China, but significant deviations were identified for patients from Japan and South Africa. In Russia, at the St. Petersburg Research Institute of Nephrology, a good agreement between the results of calculations of glomerular filtration rate CKD-EPI and the results of reference clearance methods in Caucasian patients was confirmed; the method is recommended for use in outpatient practice(question about the effectiveness of using modified equations in heterogeneous racial-ethnic groups Russian population not yet studied).

The formula is not suitable for children.

Units: ml/min/1.73 m2.

Reference values: >60 ml/min/1.73 m2.

Interpretation of the result:

A result below 60 ml/min/1.73 m2 is considered pathological. Limitations in the use of the test - see the “Description” section.

Designation	Characteristics of kidney function	GFR, ml/min/1.73 m2
C1	High and optimal	>90
C2	Slightly reduced*	60–89
C3a	Moderately reduced	45–59
S3b	Significantly reduced	30–44
C4	Sharply reduced	15–29
C5	End-stage renal failure

*relative to the level in young people

Questions
and answers

I am 40 years old, they diagnose VSD according to hypertensive type, blood pressure 150/100. What tests should be done to rule out hypertension?

There is a group of diseases with increased blood pressure. One of them - vegetative-vascular dystonia(VSD) of the hypertensive type, which is based on functional cardiovascular disorders caused by impaired autonomic activity nervous system. These disturbances are usually temporary.

A persistent increase in blood pressure can be observed in hypertension or secondary arterial hypertension. The latter most often accompany kidney disease, stenosis (narrowing) renal artery, primary hyperaldosteronism, pheochromocytoma and Cushing's syndrome. The mentioned endocrine diseases are characterized by excessive production of adrenal hormones, which causes an increase in blood pressure.

To determine the reasons arterial hypertension recommended:

24-hour urine analysis for metanephrines and free cortisol, blood test for aldosterone-renin ratio, cholesterol and its fractions, glucose, determination of glomerular filtration rate of the kidneys, general clinical analysis of blood and urine;
ECG, EchoCG, ultrasound of head and neck vessels, renal vessels, kidneys and adrenal glands;
consultation with a therapist, neurologist, cardiologist and ophthalmologist (for examination of the fundus).

Did the answer to the question help you?

Not really

I need to get my kidneys checked. What tests can be done to judge the possibility of an inflammatory process or to rule out a kidney problem?

The kidneys are a paired organ that ensures the removal of metabolic end products, toxic substances from the body, maintaining the level of electrolytes, acid-base balance and blood pressure.

If you suspect the development of inflammatory kidney diseases, you should consult a physician, urologist or nephrologist.

Did the answer to the question help you?

Not really

In this section you can find out how much it costs to complete this study in your city, read the test description and results interpretation table. Choosing where to take the Glomerular Filtration Rate (CKD-EPI) test creatinine equation)" in Moscow and other cities of Russia, do not forget that the price of the analysis, the cost of the procedure for taking biomaterial, methods and timing of research in regional medical offices may differ.

In contact with

Classmates

Factors that change the kidney 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.

Return to contents

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.

Return to contents

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. The main disadvantage of this calculation method is 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.

Increase in GFR - more a rare event, but appears when diabetes mellitus in the early stages, hypertension, systemic development of lupus erythematosus, 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 is happening in the following way:

The capillaries of the kidneys are lined from the inside with 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, the 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.

At normal healthy person In middle age, 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 a additional examination patient to find out if 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,
prostate tumors 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 functional state kidneys, its decline 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. Impairment of the concentration function of the kidneys and sometimes even a slight increase in 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. At chronic glomerulonephritis a decrease in GFR may be due to azotemic vomiting and diarrhea.

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 expected

An increase in GFR is observed in chronic glomerulonephritis with nephrotic syndrome, in early stage 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 exceed up to 30% true volume 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, H2 antagonists are prescribed to improve the accuracy of determining endogenous creatinine clearance -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 cleansed 60 times per day. Normal blood pressure is 20 mmHg. 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 of 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 nursing service.

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

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 breakdown product of protein. 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 V 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 represents capillaries basement membrane and a 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 a healthy person of 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. Clearance for this substance is called .

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 the signs. The picture of indications can be distorted by the content of drugs in the blood.

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. Smaller readings indicate incorrect urine collection.

The simplest way to assess kidney function is to measure serum creatinine levels. The higher this indicator, the lower the GFR. That is, the higher the filtration rate, the lower the creatinine content in the urine.

Glomerular filtration analysis is done if there is a suspicion of.

What diseases can be identified?

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

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 cause may be low blood pressure, shock, or 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?

The Schwartz formula is used to study GFR in children.

The speed of blood flow in the kidneys is higher than in the brain and heart itself. This is a necessary condition for the 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 sufficient 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 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 and a painful state. 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. When their functioning is disrupted, many organs malfunction, and the blood carries harmful substances, 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 begin timely treatment.

A healthy kidney consists of 1-1.2 million units of renal tissue - nephrons, functionally associated with blood vessels. Each nephron is about 3 cm long, in turn, consists of a vascular glomerulus and a system of tubules, the length of which in a nephron is 50 - 55 mm, and all nephrons are about 100 km. In the process of urine formation, nephrons remove metabolic products from the blood and regulate its composition. 100–120 liters of so-called primary urine are filtered per day. Most of the liquid is absorbed back into the blood - with the exception of substances that are “harmful” and unnecessary for the body. Only 1–2 liters of secondary concentrated urine enters the bladder.

Due to various diseases, nephrons fail one after another, mostly irreversibly. The functions of the dead “brothers” are taken over by other nephrons; at first there are so many of them. However, over time, the load on efficient nephrons becomes more and more - and, having become overworked, they die faster and faster.

How to evaluate kidney function? If it were possible to accurately count the number of healthy nephrons, this would probably be one of the most accurate indicators. However, there are other methods. You can, for example, collect all the patient’s urine for a day and simultaneously analyze his blood - calculate creatinine clearance, that is, the rate of purification of this substance from the blood.

Creatinine is the end product of protein metabolism. The normal level of creatinine in the blood is 50-100 µmol/l in women and 60-115 µmol/l in men; in children these figures are 2-3 times lower. There are other normal indicators (not higher than 88 µmol/l); such discrepancies partly depend on the reagents used in the laboratory and on the development of the patient’s muscle mass. With well-developed muscles, creatinine can reach 133 µmol/l, with low muscle mass - 44 µmol/l. Creatinine is formed in muscles, so its slight increase is possible in severe muscle work and extensive muscle injuries. All creatinine is excreted by the kidneys, approximately 1-2 g per day.

However, even more often, to assess the degree of chronic renal failure, an indicator such as GFR is used - glomerular filtration rate (ml/min).

NORMAL GFR ranges from 80 to 120 ml/min, lower in older people. GFR below 60 ml/min is considered the onset of chronic renal failure.

Here are several formulas that allow you to evaluate kidney function. They are quite well known among specialists, I quote them from a book written by specialists from the dialysis department of the St. Petersburg city Mariinsky hospital (Zemchenkov A.Yu., Gerasimchuk R.P., Kostyleva T.G., Vinogradova L.Yu., Zemchenkova I .G. “Life with chronic kidney disease”, 2011).

This, for example, is the formula for calculating creatinine clearance (Cockcroft-Gault formula, after the names of the authors of the formula: Cockcroft and Gault):

Ccr = (140 – age, years) x weight kg/ (creatinine in mmol/l) x 814,

For women, the resulting value is multiplied by 0.85

Meanwhile, in fairness, it must be said that European doctors do not recommend using this formula to assess GFR. For more precise definition For residual kidney function, nephrologists use the so-called MDRD formula:

GFR = 11.33 x Crk –1.154 x (age) – 0.203 x 0.742 (for women),

where Crк is blood serum creatinine (in mmol/l). If the test results give creatinine in micromoles (μmol/L), this value should be divided by 1000.

The MDRD formula has a significant drawback: it does not work well at high GFR values. Therefore, in 2009, nephrologists developed a new formula for estimating GFR, the CKD-EPI formula. The results of estimating GFR using the new formula are consistent with the results of MDRD at low values, but provide a more accurate estimate at high values of GFR. Sometimes it happens that a person has lost significant amount kidney function and his creatinine is still normal. This formula is too complex to present here, but it is worth knowing that it exists.

And now about the stages of chronic kidney disease:

1 (GFR greater than 90). Normal or increased GFR in the presence of a disease affecting the kidneys. Observation by a nephrologist is required: diagnosis and treatment of the underlying disease, reducing the risk of developing cardiovascular complications

2 GFR=89-60). Kidney damage with moderate reduction in GFR. Assessment of the rate of progression of CKD, diagnosis and treatment is required.

3 (GFR=59-30). Average degree decrease in GFR. Prevention, detection and treatment of complications are necessary

4 (GFR=29-15). Pronounced degree of reduction in GFR. It's time to prepare for replacement therapy (a choice of method is required).

5 (GFR less than 15). Kidney failure. Initiation of renal replacement therapy.

Estimation of glomerular filtration rate according to the level of creatinine in the blood (abbreviated MDRD formula):

Read more about kidney function on our website:

* P

Clinical significance of glomerular filtration rate

Glomerular filtration rate in nephrology is a parameter of paramount importance, since this indicator determines the functional capacity of the kidneys. Regardless of the causes of renal dysfunction (decrease), the glomerular filtration rate decreases. There is a clear correlation between the severity of kidney disease and GFR. Glomerular filtration rate begins to decline in the earliest stages of renal dysfunction (much before the occurrence first symptoms of the disease). Kidney pathology can be acute (develop over several hours or days) and chronic (slowly progress over several months or years).

Depending on the glomerular filtration rate, it is possible to determine acute and chronic kidney diseases, which can progress to the terminal stage (in this case, the patient’s life will depend on renal replacement therapy - dialysis). In case of acute renal failure, the patient may be prescribed a single short-term dialysis; for chronic renal failure - lifelong dialysis or kidney transplantation.

Note that currently the theory of “acute kidney injury” dominates among specialists, which expands the possibilities of interpreting pathophysiological processes that occur when metabolic processes in the renal parenchyma are disrupted due to the action of various etiological factors(for example, with the nephrotoxic effect of xenobiotics, hemodynamic disorders, etc.). In some cases, such disorders cause an increase in the concentration of metabolites (urea and creatinine), which is considered to be acute renal failure. But the introduction of more sensitive markers of damage to the kidney structure makes it possible to carry out early diagnosis, thus providing effective therapy damaged kidneys.

Studies have shown that when ultrafiltration in the renal glomeruli is impaired, which is recorded by determining GFR, not only significant disturbances in intrarenal metabolic processes occur, but also a significant activation of various pathological processes, typical of the so-called “diseases of civilization”, considered as a pandemic of metabolic pathologies (primarily diseases of the cardiovascular system: atherosclerosis and its complications - ischemic stroke, myocardial infarction, etc.). As a result, today specialists have begun to use a new integral concept - “chronic kidney disease” (CKD). This definition should be understood as a total pathophysiological condition with associated various kinds nosological disorders. That is, chronic kidney disease is a laboratory diagnosis with certain clinical consequences.

Estimation of glomerular filtration rate by blood creatinine level

Although high concentrations of urea and creatinine in the blood are a sign of a decrease in glomerular filtration rate, these indicators are not considered a direct measurement of it. The concentration of these metabolites increases when renal function decreases by more than 50%. That is, based on creatinine and urea levels, kidney disease cannot be detected at an early stage. Of course, this does not apply to the diagnosis of acute renal failure, the development of which occurs so quickly that the glomerular filtration rate in any case decreases by more than 50%. With normal values of urea and creatinine concentrations in the blood, acute renal failure can be safely excluded. But this is not enough to safely exclude chronic renal failure.

Glomerular filtration rate is ideally assessed by direct measurement. Such a measurement can be carried out, but this method is very complex and expensive, so it is practically not used in everyday practice. Until recently, glomerular filtration rate was determined using a test creatinine clearance: the level of creatinine in the blood plasma and the level of creatinine in the daily urine sample are determined. This method has many disadvantages, one of which is the collection of 24-hour urine. Today this test is practically not used - since 1999, glomerular filtration rate is calculated using a modified formulaMDRD.

GFR = 186 × ([creatinine in serum (plasma) + 88.4] -1.154) × age -0.0203 × 0.0742 (for women) × 1.21 (for blacks),

where the unit of measurement SCF is ml/min; creatinine blood serum (plasma) - µmol/l; age- full years.

In addition, GFR can be calculated using the MDRD formula (Am. J. Kidney Dis, 2002), based on age, gender, race, and concentrations of creatinine (mmol/L), urea (mmol/L), and albumin (g/dL). ) in blood:

GFR = 170 × (creatinine x 0.0113) -0.999 × age 0.176 × (urea x 2.8) -0.17 × albumin 0.318

The resulting value for women is multiplied by 0.762, for people of the Negroid race - by 1.18.

The latter method of assessment makes it possible to determine the value of the glomerular filtration rate in most patients without resorting to urine collection (that is, without measuring urine output and creatininuria), thereby reducing costs while maintaining clinical information.

Research has shown that calculation method calculations of glomerular filtration rate are much more accurate, as well as more convenient and cheaper than the previously used creatinine clearance. The MDRD method is recommended by many leading medical and scientific institutions and has been mastered by many modern laboratories.

Table 1 shows the values of glomerular filtration rate and the corresponding stages of chronic renal failure.

TABLE 1. Glomerular FILTRATION RATE (GFR) IN CHRONIC RENAL FAILURE (CRF)

Stage	GFR, ml/min	description
		Renal function is normal. There are signs of kidney disease (for example, protein in the urine)
		Moderate decrease in kidney function

		Significant decrease in kidney function
		A sharp decrease in kidney function
		End-stage renal failure

Note that modern standards recommend determining the level of creatinine and GFR in all patients chronic diseases kidneys every 3-12 months (frequency of tests depends on the degree of kidney damage). In addition, persons with high risk development of kidney disease, it is recommended to conduct a study every 12 months.

Recommendations for annual determination of creatinine level in blood serum (plasma)

Regular blood creatinine testing is recommended for adults at high risk of developing chronic pathology kidney Such patients include:

Diabetes
Cardiac ischemia
Various pathologies associated with atherosclerosis
Heart failure
Hypertonic disease
Rheumatoid arthritis
Kidney stone disease
Systemic lupus erythematosus
Persistent proteinuria
Myeloma
Hematuria of unknown etiology
Patients taking long time drugs with potential nephrotoxic effects

Accurate estimation of glomerular filtration rate

It is necessary to pay attention to the fact that the MDRD formula allows only a rough estimate of the glomerular filtration rate. This formula cannot be used in case of acute renal failure (although in case of acute renal failure this may not be done - it is enough to know the level of urea and creatinine in the blood).

Another significant drawback of this formula is that the data obtained with its help can be mistaken for reduced kidney function in people with normal (or almost normal) glomerular filtration rate (60-90 ml/min). That is, using only this formula, you can mistakenly diagnose stage 1 or 2 chronic renal failure in persons with absolutely normal function kidney It was this problem that prompted experts to develop a more accurate formula for calculating glomerular filtration rate based on the level of creatinine in the blood.

In 2009, research was carried out on the formula CKD-EPI, which showed that it can be used to much more accurately determine the glomerular filtration rate in individuals with normal or slightly reduced renal function. Most likely, the CKD-EPI formula will completely replace MDRD in the near future.