[Plasma creatinine, Cockcroft and MDRD: validity and limitations for evaluation of renal function in chronic kidney disease]

The glomerular filtration rate (GFR) is the best indicator of renal function. Measurement of the plasma creatinine level is the simplest laboratory test for estimating GFR. The plasma creatinine assay is currently being standardized, which will improve its reproducibility. It remains the best indicator for the diagnosis and follow-up of acute renal failure. Conversely, diagnosis and follow-up of chronic kidney disease are based on the GFR value, which is routinely estimated from formulas derived from plasma creatinine levels. The formula developed from the MDRD study performs better than the Cockcroft formula for nearly all patients and clinical situations and should replace it. GFR should be measured directly, by the urinary clearance of exogenous markers, in any situation in which the precision of the formula used is insufficient for medical decision-making. This requires defining for any given patient and situation both the desired precision and that expected from the formulas.