[Estimating renal function based on creatinine clearance: application of different formulas and correction for obese patients].

OBJECTIVE: To determine whether glomerular filtration rate (GFR) is best estimated by the Cockcroft-Gault formula or the formula used in the 'Modification ofdiet in renal disease' (MDRD) study.

DESIGN: Descriptive inventory.

METHOD: Passing-Bablok regression analysis was performed using the statistics program 'Analyse it' for the estimated GFR derived by both formulas based on 467 patients who had data on height, weight and creatinine clearance entered into the laboratory information system of the Máxima Medical Centre, Veldhoven, the Netherlands, during a 2-year period. The performance of each formula was analysed in different patient groups based on weight.

RESULTS: The MDRD formula and the Cockcroft-Gault formula performed similarly in all weight groups with adequate precision, particularly when the corrected Cockcroft-Gault formula was used for patients with a body-mass index (BMI) >25 kg/m2. The fact that outcomes using the BMI-corrected Cockcroft-Gault formula strongly correlated with outcomes calculated using the so-called Salazar-Corcoran formula, which was developed specifically for use in obese patients, confirms the validity of the BMI-corrected approach.

CONCLUSION: The Cockcroft-Gault formula and the MDRD formula both provided appropriate estimates of GFR and were also considerably more suitable for screening for renal function than assessment of plasma creatinine concentration. However, the best non-invasive way to determine GFR remains a carefully performed assessment ofcreatinine clearance using plasma and 24-hour urine samples.