Low serum C4 concentrations in type-1 diabetes mellitus.

Serum levels of complement factors C3 and C4 were investigated in 64 insulin-dependent diabetic children and 52 healthy controls. The mean value of C4 was significantly lower in diabetic than in control subjects (27.99 +/- 8.01 vs 32.03 +/- 8.91 mg/dl; P less than 0.01). Sixteen out of 64 children had serum C4 levels below the normal range; 6 out of these 11 patients had microalbuminuria. This study demonstrates low serum levels of C4 in insulin-dependent diabetes; this reduction is not related to the duration nor to the degree of metabolic control. There is a high prevalence of microalbuminuria in patients with a low C4 concentration.