Assessment of glomerular filtration rate in healthy subjects and normoalbuminuric diabetic patients: validity of a new (MDRD) prediction equation

Background. Based on the data derived from the Modification of Diet in Renal Disease (MDRD) study, a new equation was developed for the estimation of glomerular filtration rate (GFR). This equation, which takes into account body weight, age, sex, serum creatinine, race, serum urea, and serum albumin, provided a more accurate estimation of GFR in patients with renal insufficiency. However, this prediction equation has not been validated in subjects with normal or supra-normal GFR. Methods. In a cross-sectional study, we measured GFR by inulin clearance in 46 healthy controls and 46 non-complicated type I diabetic patients. In this study population, GFR was predicted by measured creatinine clearance, the Cockcroft-Gault formula, and the MDRD equation. Results. In the healthy subjects, mean GFR (+/-SD) was 107 +/- 11 as compared to 122 +/- 18 ml/min per 1.73 m(2) in the diabetic patients. This difference in GFR was reflected by a lower serum creatinine (76 +/- 8 vs 71 +/- 8 mumol/l) in the diabetic patients. In the healthy controls, median absolute differences (and the 50th-75th-90th percentile of percentage absolute differences) between predicted and measured GFR were 5.2 ml/min per 1.73 m(2) (4.9-9.8-18.5%) for creatinine clearance, 9.0 ml/min per 1.73 m(2) (8.6-14.3-24.6%) for the Cockcroft-Gault formula, and 10.7 ml/min per 1.73 m(2) (10.9-16.3-25.5%) for the MDRD equation. In the diabetic patients, these differences were 8.3 ml/min per 1.73 m(2) (7.6-9.3-13.0%) for creatinine clearance; 11.8 ml/min per 1.73 m(2) (10.1-16.0-22.5%) for the Cockcroft-Gault formula, and 18.8 ml/min per 1.73 m(2) (16.0-24.2-31.9%) for the MDRD equation. Conclusions. In subjects with a normal or increased GFR, the new MDRD-prediction equation of GFR is less accurate than creatinine clearance or the Cockcroft-Gault formula, and offers no advantage.