Changing glomerular filtration with progression from impaired glucose tolerance to Type II diabetes mellitus

Glomerular filtration rate (iothalamate clearance) was measured serially fo r 48 months in 26 Pima Indians with impaired glucose tolerance and 27 with normal glucose tolerance. At baseline, the mean glomerular filtration rate (SEM) was 133 +/- 8 ml/min in subjects with impaired glucose tolerance and 123 +/- 5 ml/min in those with normal glucose tolerance (p = 0.12). In the 12 subjects with impaired glucose tolerance who progressed to Type II (non- insulin-dependent) diabetes during follow-up, mean glomerular filtration ra te increased by 30% (p = 0.011). Among the remaining 14 subjects with impai red glucose tolerance, 12 reverted to normoglycaemia. The glomerular filtra tion rate both at baseline and after 48 months in this subgroup exceeded th e values of subjects with normal glucose tolerance by 20% (p = 0.008) and 1 4% (p = 0.013), respectively. A pronounced rise in the glomerular filtratio n rate occurs at the onset of Type II diabetes but a trend to hyperfiltrati on is also present in these with impaired glucose tolerance.