Patterns of Hyperinsulinaemia in Type 1 Diabetic Patients With and Without Nephropathy

The prevalence and patterns of insulinaemia in five groups of patients with Type 1 diabetes have been reinvestigated using a free insulin assay which minimizes in vitro redistribution of the free and antibody‐bound insulin components. In 18 diabetic patients managed by conventional insulin injection treatment and 19 patients treated by continuous subcutaneous insulin infusion (CSII), the mean 24‐h serum free insulin level exceeded a non‐diabetic reference range in 78% (injections) and 68% (CSII). Twenty‐four‐hour profiles showed that hyperinsulinaemia occurred in the basal state before meals and at night, but not immediately post‐prandially. The serum free insulin concentration at 0800 h, 1200 h, and 1600 h was significantly (p < 0.001) correlated with mean 24‐h free insulin in injection‐treated and CSII patients, and samples at one of these time‐points may thus provide a simple, single measure of integrated insulinaemia for population studies. There was no significant difference in 24‐h mean free insulin levels in 7 patients randomly crossed‐over between injection treatment and CSII, but the profiles had a more physiological pattern during CSII, with a mean post‐prandial serum free insulin level which was significantly higher on CSII than injections (mean ± SE = 37.2 ± 3.1 vs 26.9 ± 2.5 mU I‐1, p = 0.01). Fourteen diabetic patients with reagent strip‐positive proteinuria and a GFR of 32 ± 5.5 (±SE) ml min‐1 had significantly higher mean 24‐h serum free insulin levels than a pair‐matched group of diabetic patients without proteinuria (39.6 ± 5.3 vs 22.6 ± 1.8 mU I‐1, p = 0.008). As hyperinsulinaemia has been associated with an increased risk of atherosclerosis, the confirmation of significant hyperinsulinaemia in Type 1 diabetic patients on both conventional treatment and CSII is of interest; it is possible that accentuated hyperinsulinaemia in diabetic patients with nephropathy may contribute to the high frequency of cardiovascular disease in this group.