Residual C-peptide excretion is associated with a better long-term glycemic control and slower progress of retinopathy in type I (insulin-dependent) diabetes mellitus

We evaluated the progression of microangiopathic lesions in 22 type I diabetic patients with residual C-peptide excretion and in 22 type I diabetic patients matched for age at onset and disease duration without residual C-peptide excretion. We also wished to elucidate whether certain HLA-DR phenotypes were associated with preserved insulin secretory activity and/or microvascular lesions. The two groups of patients were investigated in 1984 and 1985. In the previous report, we observed less frequent signs of early microangiopathic lesions in association with a lower HbA_1c in the group with a detectable urinary C-peptide excretion. The HbA_1c level has been measured regularly (7–12 times) since the initial investigation; the mean value was lower in the patient group with residual C-peptide excretion than in the non-C-peptide group (p = 0.01). Nine of the patients in the group without urinary C-peptide excretion had increased severity of retinopathy, but only two in the group with urinary C-peptide excretion (p = 0.04) had progression of retinopathy. Incipient and/or manifest albuminuria was observed in six of the nonexcretor group and one of the C-peptide excretors. Four of the patients were receiving antihypertensive treatment and three others had a diastolic blood pressure ≥ 90 mmHg in the non-C-peptide excretor group as compared with one with a pressure ≥ 90 mmHg in the C-peptide excretor group. All 16 patients with moderate to advanced nonproliferative background retinopathy and/or incipient albuminuria had HLA-DR $\text{3}\text{4}$, $\text{3}\text{x}$, or $\text{4}\text{x}$ antigens, as compared with 20 of 28 patients with few if any signs of microangiopathy. We conclude that urinary C-peptide excretion together with regular measurements of HbA_1c may be used for prognostic evaluation of the increase in severity of retinopathy in groups of patients with type I diabetes.