Instability of fasting blood glucose values in noninsulin-dependent diabetic patients with long-term insulin treatment

Abstract

We studied serum free C-peptide immunoreactivity (CPR) and the coefficient of variation (CV) of fasting blood glucose values (FBG) in 26 insulin-treated patients with non-insulin-dependent diabetes mellitus (NIDDM) in relation to the duration of insulin treatment. Serum free CPR responses during 100 g oral glucose tolerance test (OGTT) were significantly lower in patients with insulin treatment for five years or more than in those with insulin treatment for less than five years although their previous immunoreactive insulin (IRI) responses during OGTT before insulin treatment showed no significant difference. CV of FBG was found to be significantly higher at the time of this study (20.6 ± 7.8%, mean ± SD) than at the second year of insulin treatment (15.3 ± 7.7%, P < 0.05) in the patients with insulin treatment for five or more years but did not show any significant difference in patients with insulin treatment for less than five years at the corresponding times. Thus we measured CV of the FBG in NIDDM patients at various intervals during the long-term insulin or oral hypoglycemic agent treatment in another study. In 20 patients with insulin treatment, CV of FBG was found to be significantly different among the various intervals during insulin treatment ( P < 0.0025). It was significantly higher at the eight year (22.2 ± 8.6%) and 12th year (21.9 ± 9.1%) than at the second year (14.9 ± 6.1%) and fifth year (15.0 ± 6.7%) of insulin treatment ( P < 0.025, P < 0.025; P < 0.05, P < 0.01, respectively). However, in 15 overt NIDDM patients with oral hypoglycemic agent treatment (FBG more than 180 mg/dL before treatment for all). There was no significant difference in the CV of FBG among the various intervals of treatment. The data suggested that the regulatory capacity of FBG in long-term insulin treated NIDDM patients decreases. Although the decrease of endogenous insulin secretion may be a factor, the mechanism needs to be further clarified.