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.
The Cockcroft & Gault formula, in medicine, allows the estimation of creatinine clearance in adults. This clearance being very close to the glomerular filtration rate provides information on the state of renal function.
This formula was proposed by Donald W. Cockcroft and Henry Gault in 1976.
ClCr= ((140 - âge) x poids (kg) )x F) 7,2 x créatininémie (mg/l)
ClCr: estimate of creatinine clearance in mL/min;
Cr: serum creatinine in mg/L;
Age: age in years;
Weight: body mass in kg;
K: coefficient which is 1 in men and 0.85 in women.
This formula is not applicable to the following patients:
child (using the Schwartz formula);
obese patient (body mass index > 30);
pregnant woman ;
cirrhotic with ascites;
age over 65;
and during any acute pathology (especially acute renal failure) in general.
The so-called MDRD formula is valid in certain cases where the Cockroft formula is not applicable.
A GFR of less than 90 mL/min/1.73 m2 for more than three months makes it possible to define the stages of chronic renal failure.