Residual β-cell function and microvascular complications in type 1 diabetic patients

To determine the influence of residual beta-cell function on retinopathy and microalbuminuria we measured basal C-peptide in 50 type 1 diabetic outpatients aged 24.96 +/- 7.14 years, with a duration of diabetes of 9.1 +/- 6.2 years. Forty-three patients (86%) with low C-peptide (<0.74 ng/ml) had longer duration of diabetes than 7 patients (14%) with high C-peptide (greater than or equal to 0.74 ng/ml) (9 (2-34) vs 3 (1-10) years, P = 0.01) and a tendency to high glycated hemoglobin (HBA(1)) (8.8 (6-17.9) vs 7.7 (6.9-8.7)%, P = 0.08). Nine patients (18%) had microalbuminuria (two out of three overnight urine samples with an albumin excretion rate (AER) greater than or equal to 20 and <200 mu g/min) and 13 (26%) had background retinopathy. No association was found between low C-peptide, microalbuminuria and retinopathy and no difference in basal C-peptide was observed between microalbuminuric and normoalbuminuric patients (0.4 +/- 0.5 vs 0.19 +/- 0.22 ng/ml, P = 0.61) and between patients with or without retinopathy (0.4 +/- 0.6 vs 0.2 +/- 0.3 ng/ml, P = 0.43). Multiple regression analysis showed that duration of diabetes (r = 0.30, r(2) = 0.09, P = 0.031) followed by HBA(1) (r = 0.41, r(2) = 0.17, P = 0.01) influenced basal C-peptide, and this duration of diabetes was the only variable affecting AER (r = 0.40, r(2) = 0.16, P = 0.004). In our sample of type 1 diabetic patients residual beta-cell function was not associated with microalbuminuria or retinopathy.