Estimation of renal function in diabetic nephropathy. Comparison of five methods.

Plasma as well as renal clearance of 51Cr-EDTA, serum creatinine, plasma beta-2-microglobulin and endogenous creatinine clearance were compared and evaluated in patients with diabetic nephropathy and in control patients with renal disease of other origin. The difference between the plasma clearance and the renal clearance of 51Cr-EDTA, that is the extrarenal clearance, was found to be higher in diabetics than in control patients (7.0 vs. 3.5 ml/min; p less than 0.001). The serum creatinine correlated well with the glomerular filtration rate (GFR), but in the individual case the GFR was not at all predictable from serum creatinine. The plasma beta-2-microglobulin did not correlate better than serum creatinine to 51Cr-EDTA clearance, and did not permit an earlier diagnosis of renal insufficiency. Endogenous creatinine clearance overestimated GFR by 0-180%. Due to residual urine, the coefficient of variation was higher in diabetic patients than in controls, but the effect of this imperfection was reduced by using multiple collection periods. In conclusion, the renal clearance of 51Cr-EDTA was found to be preferable to the other methods.