The kidneys are an extremely important organ for the human body. To assess their condition and performance, there are many methods and tests. One such indicator is the glomerular filtration rate.
What is this
This indicator is the main quantitative characteristic of the function of the kidneys. It reflects how much primary urine is formed in the kidneys over a certain period of time.
The glomerular filtration rate can change under the influence of various factors affecting the body.
This indicator plays a significant role in the diagnosis of kidney failure and some other diseases. To determine it, you need to know some constants reflected in the calculation formulas, of which there are several variations and varieties.
Normally, the glomerular filtration rate is regulated by several body systems (such as kallikrein-kinin, renin-angiotensin-aldosterone, endocrine, etc.). Atpathology, most often a lesion of the kidney itself or a malfunction of one of these systems is detected.
What does this indicator depend on and how can it be determined?
Factors influencing GFR changes
As mentioned above, the glomerular filtration rate depends on several indicators or conditions.
These include:
- Speed of renal plasma flow. It is due to the amount of blood flowing through the afferent arteriole to the renal glomeruli. Normally, this indicator in a he althy person is about 600 ml per minute (the calculation was carried out for an average person weighing about 70 kg).
- Pressure in vessels. Normally, the pressure in the afferent vessel should be much greater than in the efferent one. Only then can the process that underlies the work of the kidneys, filtration, be carried out.
- Number of functioning nephrons. As a result of some diseases, a decrease in the number of working kidney cells is possible, which will result in a decrease in the so-called filtration surface, and, accordingly, a low glomerular filtration rate will be detected.
Indications for determining GFR
In what cases is it necessary to determine this indicator?
Most often, the glomerular filtration rate (the norm of this indicator is 100-120 ml per minute) is determined in various kidney diseases. The main pathologies in which it is necessary to determine it are:
Glomerulonephritis. Leads to a decrease in the number of functioning nephrons
- Amyloidosis. Due to the formation of an insoluble protein compound - amyloid - the filtration capacity of the kidney decreases, which leads to the accumulation of endogenous toxins and poisoning of the body.
- Nephrotoxic poisons and compounds. Against the background of their intake, it is possible to damage the renal parenchyma with a decrease in all its functions. Sublimate and some antibiotics can act as such compounds.
- Renal failure as a complication of many diseases.
These conditions are the main conditions in which a below-normal glomerular filtration rate can be observed.
Methods for determining glomerular filtration rate
Currently, quite a lot of methods and tests have been created to determine the level of glomerular filtration. All of them have a nominal name (in honor of the scientist who discovered this or that sample).
The main ways to study the function of the glomeruli are the Reberg-Tareev test, the determination of the glomerular filtration rate using the Cockcroft-Gold formula. These methods are based on changing the level of endogenous creatinine and calculating its clearance. Based on its changes in blood plasma and urine, a certain conclusion is made regarding kidney function.
All people can carry out these tests, since these studies have no contraindications.
The above two samples are the reference in the studyrenal filtration. Other methods are used less frequently and are carried out mainly for specific indications.
How is the creatinine level determined and what are these procedures?
Rehberg-Tareev test
Slightly more common in clinical practice than the Cockcroft-Gold test.
For research, blood serum and urine are used. Be sure to take into account the time of collection of analyzes, since the accuracy of the study depends on this.
There are several variants of this sample. The most common technique is the following: urine is collected over several hours (usually two-hour portions). In each of them, creatinine clearance and minute diuresis (the amount of urine formed per minute) is determined. The calculation of the glomerular filtration rate is based on these two indicators.
Somewhat less often, the determination of creatinine clearance in a daily portion of urine or the study of two 6-hour samples is carried out.
In parallel, no matter how the test is carried out, in the morning on an empty stomach, blood is taken from a vein to assess the concentration of creatinine.
Cockcroft-Gold test
This technique is somewhat similar to Tareev's test. In the morning, on an empty stomach, the patient is given to drink a certain amount of liquid (1.5-2 glasses of liquid - tea or water) to stimulate minute diuresis. After 15 minutes, the patient urinates into the toilet (to remove the remnants of urine formed during the night from the bladder). Then the patientpeace is shown.
After an hour, the first portion of urine is collected and the time of urination is accurately noted. During the second hour, the second portion is collected. Between urination, 6-8 ml of blood is taken from the patient's vein to determine the level of creatinine in the blood serum.
After minute diuresis and creatinine concentration are determined, its clearance is determined. How to determine the glomerular filtration rate?
The formula for calculating it is as follows:
F=(u: p) ˑ v, where
u is urinary creatinine concentration, p is plasma creatinine, V is minute diuresis, F - clearance.
Based on the F index, a conclusion is made about the filtration capacity of the kidneys.
Determining the filtration rate using the MDRD formula
Unlike the main methods to determine the glomerular filtration rate, the MDRD formula has become somewhat less common in our country. It is widely used by nephrologists in most European countries. In their opinion, the Reberg-Tareev test is low informative.
The essence of this technique is to determine GFR based on gender, age and serum creatinine. Often used in determining kidney function in pregnant women.
It looks like this:
GFR=11.33 x Crk - 1.154 x age – 0.203 x K, where
Crk is blood creatinine concentration (in mmol/l), K – gender coefficient (for example, for women it is 0.742).
This formula works well for lower filtration rate levels, but its main drawback is incorrect results if glomerular filtration rate increases. The calculation formula (due to this minus) has been modernized and supplemented (CKD-EPI).
The advantage of the formula is that age-related changes in kidney function can be determined and monitored over time.
Decline
After all the tests and studies carried out, the interpretation of the results is carried out.
Reduced glomerular filtration rate is observed in the following cases:
- Loss of the glomerular apparatus of the kidney. A decrease in GFR is practically the main indicator indicating the defeat of this area. At the same time, with a decrease in GFR, a decrease in the concentrating ability of the kidneys (in the early stages) may not be observed.
- Renal failure. The main reason for the decrease in GFR and the decrease in filtration capacity. Throughout all its stages, there is a progressive decrease in the clearance of endogenous creatinine, a decrease in the filtration rate to critical numbers, and the development of acute intoxication of the body with endogenous metabolic products.
- Reduced glomerular filtration rate can also be observed while taking some nephrotoxic antibiotics, which leads to the development of acute renal failure. These include some fluoroquinolones and cephalosporins.
Stress tests
To determine the filtration capacity, you canuse the so-called stress tests.
For loading, usually use a single use of animal protein or amino acids (in the absence of contraindications) or resort to intravenous administration of dopamine.
When loaded with protein, about 100 grams of protein enters the patient's body (the amount depends on the patient's weight).
Over the next half hour, he althy people experience an increase in GFR by 30-50%.
This phenomenon is called the renal filtration reserve, or PFR (renal functional reserve).
If there is no increase in GFR, a violation of the permeability of the renal filter or the development of certain vascular pathologies (such as diabetic nephropathy) and CRF should be suspected.
The dopamine test shows similar results and is interpreted similarly to the protein loading test.
Importance of conducting these studies
Why have so many methods for assessing filtration capacity been created and why is it necessary to determine the glomerular filtration rate?
The norm of this indicator, as you know, changes under various conditions. That is why many methods and studies are currently being created to assess the state of our natural filter and prevent the development of many diseases.
In addition, these diseases provoke most kidney transplants, which is a rather laborious and complex process, often leading to the need for repeated interventions or more complexevents.
That is why the diagnosis of the pathology of this organ is so important for both patients and physicians. A timely detected disease is much easier to treat and prevent than its advanced form.
