Tubular damage in microalbuminuric patients with primary glomerulonephritis and diabetic nephropathy

Tubular damage as suggested by enzymuria and tubular proteinuria is a recognized feature of glomerulonephritis (GN) with clinical proteinuria and both incipient and overt diabetic nephropathy (DN). However, little is known about the presence of tubulopathy in patients with primary GN, microalbuminuria [albumin excretion (AER) 30-300 mg/d] and microhematuria. Three groups were studied. The GN group comprised 17 (2 F) patients with biopsy-proven GN with microalbuminuria. The DN group comprised 35 (14 F) patients with incipient diabetic nephropathy with AER 30-300 mg/d, and controls comprised 38 (15 F) normal subjects with normal AER < 30 mg/d. Serum creatinine, albuminurinuria, transferrinuria, and markers of tubular damage such as urinary excretion of N-acetyl-glucosaminidase (NAG), leucine aminopeptidase (LAP), gamma-glutamyl transferase (gGT), and retinol binding protein (RBP) were measured. GN and DN had comparable degrees of albuminuria, transferrinuria, and LAP excretion, and these were significantly higher than controls. Serum creatinine was significantly higher in GN than DN and controls. DN had significantly higher NAG and RBP, and lower gGT than GN and controls. In both GN and DN groups, both glomerular proteins correlated with each other and NAG correlated significantly to LAP and gGT. Albuminuria correlated to tubular enzymuria in GN group but not in patients with DN. The results suggest that tubular damage is less marked in microalbuminuric patients with GN than those with DN despite similar degree of glomerular proteinuria. The pattern of tubulopathy is also different in the two groups, indicating differences in the pathogenesis of tubular damage in these two clinical settings.