In modern medicine, the term "clearance" is used, which denotes a quantitative indicator of the speed of purification of certain biological fluids. The use of this indicator allowed us to significantly expand our understanding of the pharmacokinetics and pharmacodynamics of certain substances.
So, for example, creatinine clearance is determined using a diagnostic test Rehberg-Toreev. It is worth noting that in this case it is possible to determine the filtration rate of both endogenously synthesized substances and those arriving from outside (drugs and other agents). An assessment is made by calculating the filtration intensity (in glomeruli) by the rate of plasma release from a specific substance. Accounting is carried out for a fixed time (mainly - a day).
Speaking of creatinine, it is worth paying attention to the fact that its elimination from the body occurs mainly due to the filtration activity of the kidneys. Based on this, an indicator such as creatinine clearance will be significant in relation to assessing the functioning of the glomerular filtration of the kidneys. It should be noted that this indicator characterizes not only the functional ability of the filtering system, but also some other disturbances in the functioning of human organs and systems. Changed downward, creatinine clearance may also indicate an insufficient level of blood flow in the kidneys (vascular atherosclerosis, and with sharp and acute development - thromboembolism).
Normally, a decrease in kidney activity occurs after forty years. The glomerular filtration reduction rate is 1% per year. After sixty years, the level of activity decreases somewhat faster (these changes are primarily associated with aging). However, it should be noted that any manifestations of such transformations are not observed for the reason that in old age all metabolic processes slow down, including the synthesis of endogenous creatinine.
When preparing for the Reberg test, it is necessary to exclude the use of certain drugs that can affect the course of the study (Cortisol, Furosemide, Corticotropin, Methylprednisolone, Thyroxine and others).
For sampling, a urine sample is taken and a blood test is performed for the average plasma creatinine level.
Among the indications for the purpose of the study: endocrine pathologies, assessment of the functional activity of the kidneys, as well as an assessment of the effect of physical activity.
Depending on the specific level of reduction in clearance, certain violations are determined.
- 30 ml / min / 1.7 m2 or more - a moderate decrease in renal function;
- 30-15 ml / min / 1.7 m2 - the presence of renal failure (in a compensated or subcompensated degree);
- <15 ml / min / 1.7 m2 - renal failure in the decompensation phase.
It is important to understand that the functional ability of the filtering system of the kidneys determines the clearance of creatinine, the norm of which, when conducting the Reberg test, indicates the normal state of the kidneys.
However, some diseases do not lead to changes in this indicator (for example, chronic pyelonephritis).
The level of creatinine in the blood depends both on the activity of its endogenous synthesis, and on the rate of its excretion in the urine. It is important to understand that this indicator depends not only on the activity of the filtering system, but also on the speed and volume of reabsorption of substances during the formation of primary urine.
Thus, at the present time, the Reberg test (which determines creatinine clearance) has found quite wide application in diagnostic medicine. A direct relationship between clearance and kidney function provides a high diagnostic significance of the procedure.