Diagnostic value of urinary alanine aminopeptidase and N-acetyl-β-D-glucosaminidase in comparison to α1-microglobulin as a marker in evaluating tubular dysfunction in glomerulonephritis patients

To estimate the diagnostic value of tubular parameters, the urinary alanine aminopeptidase (AAP), N-acetyl-beta-o-glucosaminidase (NAG) and the alpha(1)-microglobulin (a 1 M) of 150 patients with histologically proven glomerulonephritis (GN) were determined. In addition, the reabsorption rate of the proximal tubule and the fractional excretion of sodium, the free water clearance and the renal function were assessed by inulin and p-aminohippurate (PAH) clearance. Compared to healthy controls, urinary AAP, NAG and a 1 M were found significantly elevated in GN patients. Morphological tubular changes were confirmed by significant differences in urinary laboratory parameters. In patients with tubular atrophy, the diagnostic sensitivity and specificity were calculated as follows: AAP (0.94/0.35), NAG (0.75/0.59) and a 1 M (0.73/0.52). In patients showing tubular protein droplets, the values were 0.90/0.17 for AAP, 0.78/0.76 for NAG and 0.84/0.74 for a 1 M and in patients with interstitial fibrosis, the values were AAP (0.95/0.35), NAG (0.75/0.46) and a 1 M (68/0.38). Urinary AAP, NAG and a 1 M reflect histologically proven tubulus alteration in GN, although in most cases, the renal function is still intact. AAP indicates very early tubular impairment and, in some cases, AAP is elevated although NAG and alh? are still within normal ranges. We suggest that the enzyme activities are useful in the diagnostics of early stages of the disease. (C) 2000 Elsevier Science B.V. All rights reserved.