Service, F. John

OBJECTIVE During the Diabetes Control and Complications Trial (DCCT), intensive diabetes therapy achieving a mean HbA1c of ∼7% was associated with a threefold increase in the rate of severe hypoglycemia (defined as requiring assistance) compared with conventional diabetes therapy with a mean HbA1c of 9% (61.2 vs. 18.7 per 100 patient-years). After ∼30 years of follow-up, we investigated the rates of severe hypoglycemia in the DCCT/Epidemiology of Diabetes Inverventions and Complications (EDIC) cohort. RESEARCH DESIGN AND METHODS Rates of severe hypoglycemia were reported quarterly during DCCT and annually during EDIC (i.e., patient recall of episodes in the preceding 3 months). Risk factors influencing the rate of severe hypoglycemia over time were investigated. RESULTS One-half of the DCCT/EDIC cohort reported episodes of severe hypoglycemia. During EDIC, rates of severe hypoglycemia fell in the former DCCT intensive treatment group but rose in the former conventional treatment group, resulting in similar rates (40.8 vs. 36.6 episodes per 100 patient-years, respectively) with a relative risk of 1.12 (95% CI 0.91–1.37). A preceding episode of severe hypoglycemia was the most powerful predictor of subsequent episodes. Entry into the DCCT study as an adolescent was associated with an increased risk of severe hypoglycemia, whereas insulin pump use was associated with a lower risk. Severe hypoglycemia rates increased with lower HbA1c similarly among participants in both treatment groups. CONCLUSIONS Rates of severe hypoglycemia have equilibrated over time between the two DCCT/EDIC treatment groups in association with advancing duration of diabetes and similar HbA1c levels. Severe hypoglycemia persists and remains a challenge for patients with type 1 diabetes across their life span.

OBJECTIVE The Diabetes Control and Complications Trial (DCCT) demonstrated the beneficial effects of intensive versus conventional therapy on the development and progression of microvascular complications of type 1 diabetes. These beneficial effects were almost completely explained by the difference between groups in the levels of HbA1c, which in turn were associated with the risk of these complications. We assessed the association of glucose variability within and between quarterly 7-point glucose profiles with the development and progression of retinopathy, nephropathy, and cardiovascular autonomic neuropathy during the DCCT. RESEARCH DESIGN AND METHODS Measures of variability included the within-day and updated mean (over time) of the SD, mean amplitude of glycemic excursions (MAGE), and M-value, and the longitudinal within-day, between-day, and total variances. Imputation methods filled in the 16.3% of expected glucose values that were missing. RESULTS Cox proportional hazards models assessed the association of each measure of glycemic variation, as a time-dependent covariate, with the risk of retinopathy and nephropathy, and a longitudinal logistic regression model did likewise for cardiovascular autonomic neuropathy. Adjusted for mean blood glucose, no measure of within-day variability was associated with any outcome. Only the longitudinal mean M-value (over time) was significantly associated with microalbuminuria when adjusted for the longitudinal mean blood glucose and corrected for multiple tests using the Holm procedure. CONCLUSIONS Overall, within-day glycemic variability, as determined from quarterly glucose profiles, does not play an apparent role in the development of microvascular complications beyond the influence of the mean glucose.

Three normal, three stable diabetic, and eight unstable diabetic subjects were investigated, with continuous automated blood glucose analysis for forty-eight-hour periods, during metabolic balance studies of six days' duration under near normal conditions (fed and ambulatory) after the attainment of clinically optimal diabetic regulation. The studies on unstable diabetics were performed during constant dietary intake, with one or two daily injections of intermediate-acting insulin and then repeated with four daily injections of short-acting insulin. A characteristic of blood glucose behavior, the mean amplitude of glycemic excursion (MAGE), was measured. MAGE was small for normals (range, 22 to 60 mg./100 ml.), larger for stable diabetics (67 to 82 mg./100 ml.), and largest for unstable diabetics (119 to 200 mg./100 ml.). Associated with a significant decrease (p = 0.004) in the mean diurnal glycemic level (from 146 to 244 mg,/100 ml. to 101 to 152 mg./100 ml.) achieved through the use of four daily doses of short-acting insulin there was a significant increase (p = 0.006) in hypoglycemic episodes (from 0 to 4/48 hr. to 3 to 6/48 hr.) without significant change in MAGE. The persistently large value of MAGE despite therapy with multiple injections of short-acting insulin appears to be a characteristic of unstable diabetes.