β
βIn clinical practice, however,
creatinine clearance is used to measure GFR.
Creatinine is produced naturally by the body (
creatinine is a metabolite of creatine, which is found in muscle). It is freely filtered by the glomerulus, but also actively secreted by the renal tubules in very small amounts such that creatinine clearance overestimates actual GFR by 10-20%. This margin of error is acceptable considering the ease with which creatinine clearance is measured.