Does day-long absolute hypoinsulinemia characterize the patient with non-insulin-dependent diabetes mellitus?

Plasma glucose and insulin responses to a standard oral glucose tolerance test (75 g of glucose) and to mixed meals were compared in 15 normal subjects and 15 patients with non-insulin-dependent diabetes mellitus (NIDDM). Fasting plasma glucose levels were above 140 mg/dL in all patients with NIDDM, and the two groups were weight matched. Plasma glucose levels were significantly higher in patients with NIDDM throughout the glucose tolerance test, and this was associated with a marked reduction in plasma insulin response. Plasma glucose levels were also higher in patients with NIDDM when measured hourly from 8 AM to 5 PM (mixed meals were consumed at 8 AM and 12 PM), but the plasma insulin concentration of the two groups were similar. Thus, the day-long circulating insulin levels of patients with NIDDM are not reduced. Consequently, these patients cannot be considered to be absolutely insulin deficient.