Plasma C-peptide in long-standing type 1 diabetics with and without microvascular disease.

Plasma C-peptide levels were measured both in the fasting state and in response to a standard breakfast in 37 Type 1 (insulin dependent) diabetics with severe proliferative retinopathy, 20 Type 1 diabetics without complications and 13 non-diabetic subjects. The two diabetic groups were matched for age and duration of diabetes. Seventeen out of 37 subjects with diabetic complications had detectable C-peptide compared with three out of 20 in the group without complications (p less than 0.05). There was a significant correlation between fasting C-peptide levels when present and the increment in C-peptide (r = 0.89, p less than 0.0001). There was no correlation between C-peptide levels and the fasting blood glucose or HbA1. No evidence was found to support the hypothesis that in long-term diabetics, sufficient beta-cell function may persist which measurably influences diabetic control and prevents the development of microvascular complications.