Human urinary intestinal alkaline phosphatase as an indicator of S3-segment-specific alterations in incipient diabetic nephropathy.

Urinary enzymes were determined in a controlled study including 28 type I diabetes mellitus patients. Fifteen patients had persistent microalbuminuria and were compared to 13 normoalbuminuric patients with comparable age and sex distribution. All patients had normal renal function as measured by serum creatinine. Human intestinal alkaline phosphatase (hIAP), a specific marker of the proximal tubular S3 segment, was elevated in the urine of microalbuminuric patients while human tissue non-specific alkaline phosphatase (hTNAP), indicating effects mainly at the S1-S2 segments, was not. Urinary hIAP was correlated with serum glycated haemoglobin. These results suggest that tubular alterations are present at an early stage of diabetic nephropathy, especially at the S3 segment, and that hIAP may have promise as an early marker.