Objective: To study plasma insulin level and insulin sensitivity of nondiabetic first-degree relatives of patients in familial non-insulin-dependent diabetes mellitus (NIDDM) pedigrees.
Methods: Standard oral glucose tolerance test(OGTT) was conducted in 55 healthy controls and 97 first-degree relatives of NIDDM probands in familial NIDDM pedigrees. Plasma glucose and plasma insulin were determined at all phases after oral glucose load. Moreover, we calculated the glucose/insulin area ratio under the curve of OGTT (SGI) and the insulin sensitivity index (ISI) in all subjects to estimate their insulin sensitivity.
Results: In nondiabetic first-degree relatives, SGI and ISI were significantly decreased (P < 0.01), and plasma insulin was increased at 0, 30, 60, 120 minutes after administration of oral glucose load (P < 0.05 and P < 0.01), as compared with the controls, in matched age, body mass index (BMI) and proportion of sex. In both first-degree relatives and the insulin controls, SGI was positively correlated with ISI (r = 0.39, 0.41, respectively, P < 0.01) and both SGI and ISI were inversely correlated with BMI (r = -0.38, -0.39; -0.32, -0.25, respectively, P < 0.01). Moreover, FINS in the two groups was positively correlated with BMI (r = 0.30, 0.34, respectively, P < 0.05).
Conclusion: In nondiabetic first-degree relatives of patients in familial NIDDM pedigrees, plasma insulin level was increased and insulin sensitivity was decreased as compared with the healthy controls. It suggests that they suffered from hyperinsulinemia and insulin resistance.