Creatinine clearance measures the ratio between the rate of elimination of creatinine by the kidneys (through urine) and its concentration in the blood. Since creatinine is eliminated only by renal filtration, the measurement of its clearance makes it possible to evaluate the filtration rate of the kidneys. In the evaluation of clearance, the interpretation should take into account age, sex, weight, height, cardiac and renal function, and drug treatment (salicylates, cimetidine, trimethoprim, probenecid, etc.).
Creatinine clearance is prescribed when the kidney disease is suspected, before prescribing medications that involve having normal kidney function, and when renal blood flow is reduced due to heart disease.
This examination can also be requested after an initial blood test showing high blood creatinine.
Creatinine clearance is the plasma clearance coefficient or the number of ml of plasma completely cleared of creatinine by the kidney, related to time. It makes it possible to estimate glomerular filtration (GFR) and more generally renal function.
In a situation of equilibrium and stable plasma concentration (P), the quantity of creatinine filtered by the kidney (P x Clearance) is equivalent to the quantity eliminated in the urine (product U x V of the urinary concentration U and of the urine volume V).
Clearance can therefore be calculated using the formula:
Clearance = (U x V) / P