Creatinine is a product of energy metabolism in muscle tissues. Creatinine is formed in muscle fibres, so its amount depends on muscle mass. Its function is to provide the muscles with energy material. As the chemical precursor creatine is formed in the liver, its function also has an influence on creatinine concentration.

A special feature of creatinine is that it is not reabsorbed by the kidneys (many substances are not completely excreted by the kidneys, a certain amount goes back into the bloodstream). This factor makes it possible to determine the condition of the kidney tissue as accurately as possible. By knowing how much creatinine is in the blood and how much should be excreted, doctors prescribe a blood and urine creatinine test according to a special scheme. The formula is then used to calculate the ENDOGENIC CREATININE CLIRENS (Rehberg-Tareyev test).  A decrease in it signals impaired kidney function.  An increase indicates a pathology such as chronic glomerulonephritis with nephrotic syndrome.

Nowadays clinical pharmacologists select the right dosage of medicines according to the endogenous creatinine clearance.

It is therefore most reasonable to take a blood and urine creatinine test together.

Rehberg-Tareyev test (endogenous creatinine clearance)

The patient urinates in the morning and drinks 200ml of water. After 1 hour the patient has a blood test for creatinine and after another 1 hour the urine is taken for analysis.

The calculation is done according to the formula :

GFR - glomerular filtration rate

Uc - urine creatinine

Pc- plasma creatinine

D - minute diuresis (amount of urine (ml) in 2 hours divided by 120)

Normal in males 120±25 ml/min, in females 95±20 ml/min