PROTEIN-LOADING TEST, URINARY ALBUMIN EXCRETION AND RENAL MORPHOLOGY IN DIAGNOSIS OF SUBCLINICAL DIABETIC NEPHROPATHY

The acute effects of protein loading (1.5 g kg-1) on glomerular filtra tion rate (GFR) and urinary albumin excretion (UAE) were investigated in 2 3 type-I diabetic patients with no clinical nephropathy, and in 7 healthy subjects (controls). The results were compared with renal mor phology data. In controls and in 14 diabetic patients (group 1) GFR in creased by 27 and 37%, respectively, corresponding to normal renal res erve, but in 9 patients (group 2) GFR decreased by 20%, indicating the absence of a renal reserve. Microalbuminuria was found in none of the patients in group 1 and in 50% of patients in group 2. Two hours afte r the load UAE increased in all groups, but the increase was most mark ed in group 2, despite the fall in GFR. The two groups of patients did not differ with regard to the duration and control of diabetes, but d iffered markedly in terms of baseline GFR (131 vs. 195 ml min-1, P < 0 .01, in groups 1 and 2, respectively). Renal morphology showed minimal non-specific glomerular injury in group 1, and signs of glomeruloscle rosis in group 2. We conclude that the impaired renal response to prot ein load precedes other subclinical manifestations of diabetic renal i njury, and may be useful in the diagnosis of latent diabetic nephropat hy.