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 51Cr-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 [mumol/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 less than 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 less than 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 less than 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.