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 “harmful” and unnecessary for the body substances. 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. To more accurately determine 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 of GFR decline. 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 by the level of creatinine in the blood (abbreviated MDRD formula):

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Characteristics of the SCF method

Glomerular filtration is measured using certain substances. However, some of them have a number of disadvantages, for example, when using them, it is necessary to carry out continuous IV infusions to maintain a constant plasma concentration. In order to calculate the glomerular filtration rate during infusion, it is necessary to collect at least 4 portions of urine. Moreover, the collection interval must be strictly 30 minutes. Because of this, this research method is considered quite expensive and is used only in specialized research institutes.

Most often, GFR analysis is carried out on the basis of a study of endogenous creatinine clearance. Creatinine is the end product of the metallic process between creatine and creatine phosphate. The kidneys constantly produce and excrete creatinine. Moreover, the speed of this process directly depends on muscle mass. For example, men who exercise produce greater levels of cretinin than children, the elderly, or women.

This substance is excreted only with the help of GFR. Although some part of this substance is excreted through the proximal tubules. Therefore, the glomerular filtration rate, which is determined by creatinine clearance, is sometimes slightly overestimated. If the kidneys are functioning normally, then the overestimation does not exceed 5-10%.

If there is a decrease in glomerular filtration, then the amount of creatinine released increases. If the patient has impaired renal function, this increase can reach 70%.

How to collect urine for analysis

In order for the GFR calculation to be correct, it is necessary to analyze the daily dose of urine. However, it must be assembled correctly.

To do this, you do not need to take into account urine from the very first morning bowel movement. But everything that follows can be collected. And exactly 24 hours later you need to pick up the last batch of liquid. It must be attached to the previous materials and sent for research.

Normal creatinine in daily dose urine has the following indicators:

in men - 18-21 mg/kg; in women - 15-18 mg/kg.

If this value is much lower, this may indicate improper urine collection. Or that the patient has severe renal failure and too little muscle mass.

It must be remembered that the container in which the urine for analysis is located must be stored in a cool place. Otherwise, uncontrolled bacterial growth is possible. They will help accelerate the conversion of creatinine to creatine, which is why the clearance value will be significantly lower than normal.

We must not forget that before starting urine collection, it is necessary to determine how much creatinine is in the serum. There is a special calculation formula that will help you find out the result. The norm for women is from 75 to 115 ml/min, but for men it is from 85 to 125 ml/min.

Undoubtedly, the method of diagnosing GFR through creatinine clearance is the most accurate way to find out correct result kidney function.

How to determine the level of kidney function

The most precise definition the level of kidney function consists of analyzing creatinine clearance. The higher the creatinine level, the lower the glomerular filtration rate will be.

But one should also take into account external factors, which can significantly affect the results of the study. For example, the level of lean body mass, the patient’s weight, the diet that the patient follows, and much more.

We must not forget about the use of various medical supplies. Some of them may affect the analysis results. But still, the results of such a study cannot be neglected. After all, even the slightest change in readings can indicate the development of renal failure. Which in turn will lead to more serious illnesses.

Exist specific formula, with which you can analyze creatinine clearance. This is the Cockcroft and Galt formula, it includes the following characteristics:

patient's age; floor; weight.

It is with the help of GFR analysis that doctors diagnose the level of renal failure and make a conclusion about whether the patient needs to be connected to dialysis or undergo a kidney transplant immediately.

Beyond the results this study, other indications of the patient should be taken into account. Based only comprehensive survey the doctor can make the final decision.

Treatment of kidney failure

In addition to regular dialysis, the patient may be prescribed other methods of treating kidney failure. These may be preparations that contain calcium and other beneficial substances. Of course, the main task of the doctor is to identify the cause of the disease and begin its immediate treatment.

If we're talking about about preliminary inflammatory process, then you need to identify the type and origin of the infection, and then begin to eliminate it. In case of congenital renal failure, urgent organ transplantation is necessary.

At the same time, we must not forget that a person can live peacefully with one kidney. But for this, the level of its functioning must be above average. This can be determined using GFR analysis.

But every patient should remember that they need to see a doctor when the first symptoms of any disease occur. Only timely diagnosis and correctly prescribed treatment will help the patient restore the functioning of his body.

Of course, for this you also need to consult experienced and competent specialists and avoid self-medication methods, which can lead to very severe consequences, up to the death of a person.

Modern diagnostic methods

Today, medicine is actively developing. And there are already many ways to diagnose a patient’s health condition. For example, until recently, ultrasound examination with an ultrasound machine was considered the most important method. Then new methods began to appear: now this is the well-known computed tomography and other types of modern diagnostics.

But the GFR method for clearing creatinine remains indispensable. It is this that allows us to fully assess the performance of a person’s kidneys and identify the first signs of renal failure.

The kidneys are the main filter of the human body, and if its work is disrupted, then we can say that other organs will soon “give up their positions.”

In addition, a complete stop of kidney function leads to the death of a person. He needs constant artificial blood purification, called dialysis, and is therefore tied to a specific place, namely the hospital. At the same time, the patient cannot afford to go somewhere for a visit or on vacation, because he needs to undergo dialysis with some regularity. And it's good if it's free. Otherwise, not everyone has the financial ability to cope with this procedure.

Advantages of the research method

To say that he is the best is incorrect. It must be said that it is the most effective in comparison with other methods of diagnosing kidney function. It is with the help of this method that the doctor can determine at what speed and to what extent the kidneys can cope with their functions.

It is the method of determining GFR that helps show the real picture of kidney function.

And if it suddenly becomes clear that the kidneys are not performing their functions well, the doctor immediately applies the necessary treatment and looks for a way to help this organ using artificial methods. Most often, it is the GFR analysis that shows that the kidneys are not working well, and the patient needs an urgent transplant.

As a result, it is possible to save the patient’s life and restore his normal lifestyle.

But in order to do such an analysis, the patient must contact a professional nephrologist or urologist, and only after that he undergoes this examination.

It is always worth remembering that everything related to health must be done on time and according to established rules. Then the treatment will be effective and timely, and the result will be definitely positive.

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 normal condition it 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 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.

For the treatment of kidney diseases, our readers successfully use Galina Savina's method.

Checking kidney function using the Cockroft-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 research.

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 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

kidney disease

or improper 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.

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

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It consists of 16 most useful medicinal herbs, which have extremely high efficiency in cleansing the kidneys, in the treatment of kidney diseases, diseases urinary tract, as well as when cleansing the body as a whole.

Doctors' opinion..."

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 of 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?

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 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. 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.