Tubular function in diabetic children assessed by Tamm-Horsfall protein and glutathione S-transferase

In a previous study, we found urinary excretion of Tamm-Horsfall protein (THP) to be persistently decreased in 25% of patients during the first year after diagnosis of diabetes mellitus. We thus wanted to study another marker for distal tubular function, pi glutathione S-transferase (π-GST) and compare this and THP with proximal tubular function evaluated with α-GST and α-1-microglobulin (HC) in patients with longer duration of diabetes. One hundred and eighty-four diabetic and 16 control children were studied with timed overnight urine collections. Median age was 14 years, and median age at diagnosis was 8 years. The urinary excretion of α- and π-GST was significant lower in diabetic than control children. There were no differences in the excretion of HC and THP. Diabetic children with decreased α-GST had higher albumin excretion, HbA_1c levels, and longer diabetes duration but decreased THP excretion and cystatin-C clearance compared with those with normal excretion. In contrast, a decreased π-GST or THP excretion was not associated with such differences. Diabetic children with increased HC excretion had increased HbA_1c levels. Diabetic children, before the stage of microalbuminuria, may have signs of both proximal and distal tubular dysfunction, which is related to diabetes duration and poor metabolic control. Alpha-GST and π-GST seem to be more sensitive than other parameters studied.