KIDNEY MORPHOLOGICAL-CHANGES IN RELATION TO LONG-TERM RENAL-FUNCTION AND METABOLIC CONTROL IN ADOLESCENTS WITH IDDM

For the past 10-15 years all the children at our unit with insulin-dep endent diabetes mellitus have been repeatedly followed-up with renal f unction tests. Renal biopsy, examined by light and electron microscopy , was included in the follow-up of 36 adolescents and young adults, ag ed 13-25 years, with a disease duration of 7-19 years. All subjects ha d undergone at least three renal function tests before biopsy and none had persistent microalbuminuria. Renal function was evaluated as glom erular filtration rate and effective renal plasma flow determined by c learances of inulin and para-amino hippuric acid. Glomerular filtratio n rate and filtration fraction were increased before and at the time o f the biopsy. Glomerular basement membrane thickness (331-858 nm) and mesangial matrix volume fraction (7.4-17.1%) were increased. Long-term hyperfiltration and hyperperfusion before biopsy correlated inversely with mean glomerular volume. Increased filtration fraction before the biopsy correlated directly with mean of all HbA(1c) (r = 0.485, p < 0 .01) and both variables correlated directly with mesangial matrix volu me fraction, basement membrane thickness and structural index (r = 0.4 33, p < 0.01 and r = 0.626, p < 0.001, respectively). Urinary albumin excretion rate correlated directly with foot process width (r = 0.645, p < 0.001). By multiple regression analysis the most important variab le for the increase in basal membrane thickness was the metabolic cont rol while the mean of previous filtration fraction was most important for the increase in mesangial matrix volume. In conclusion, although n one of the patients showed constant microalbuminuria, early diabetic s tructural changes were evident with basal membrane thickening and incr eased mesangial matrix volume. The structural changes related to long- standing hyperfiltration and poor metabolic control.