ACCURATE ESTIMATION OF GLOMERULAR-FILTRATION RATE IN DIABETIC NEPHROPATHY FROM AGE, BODY-WEIGHT, AND SERUM CREATININE

OBJECTIVE - To assess, in diabetic nephropathy, the accuracy of a method that estimates glomerular function with age, body weight, and serum creatinine as parameters. RESEARCH DESIGN AND METHODS - Glomerular filtration rate (GFR) was measured 57 times in 20 subjects with insulin-dependent diabetes mellitus and nephropathy with a single injection of Cr-51-EDTA. At the same time, the estimated creatinine clearance (ml/min) was calculated with the Cockroft-Gault formula (140 - age [yr]) x body wt [kg] x K/serum creatinine [mu-mol/L]) K = 1.23 for men, 1.05 for women. These values were then corrected for body surface area (1.73 m2). RESULTS - For GFR measurements < 100 ml . min-1 . 1.73 m-2 (n = 41), there was a strong positive correlation with the estimated creatinine clearance corrected for body surface area (r = 0.94, P < 0.0001). The slope of this regression line did not differ significantly from identity or the y-intercept from zero. On average, the Cockroft-Gault formula (corrected for body surface area) underestimated the GFR by only 3.1 ml . min-1 . 1.73 m-2 (9.7 SD). CONCLUSIONS - This formula, corrected for body surface area, gives accurate estimates of GFR when GFR < 100 ml . min-1 . 1.73 m-2. This formula could be used with an acceptable degree of confidence when repeated isotope assessments of renal function in diabetic nephropathy are impracticable.