Glycemic control in diabetes mellitus: Have changes in therapy made a difference?

PURPOSE: New methods of measuring and controlling glycemia in diabetes mellitus have been developed and implemented in the past 10 years. We examined whether glycemia, as measured by glycosylated hemoglobin, changed in outpatient insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM) populations between 1985 and 1993 and whether contemporaneous changes in therapy could account for observed changes in glycemia. PATIENTS AND METHODS: Outpatients were selected based on having glycated hemoglobin (HbA(1c)) measured in the Massachusetts General Hospital laboratory during March 1985 (IDDM n = 94 and NIDDM n = 137) or during March 1993 (IDDM n = 89 and NIDDM n = 118). Chart reviews established demographic and clinical characteristics, including frequency of blood glucose self-monitoring, insulin injections, office visits, and HbA(1c) measurements during the year prior to the HbA(1c) result. RESULTS: Mean HbA(1c) level was significantly lower in the 1993 IDDM cohort compared with the 1985 cohort (8.77% +/- 1.7% versus 9.47% +/- 2.1%, P = 0.014). In the NIDDM cohorts, the difference in mean HbA(1c) did not achieve statistical significance (8.35% +/- 1.6% in 1993 versus 8.75% +/- 2.1% in 1985, P = 0.09); however, when adjusted for differences in NIDDM duration, HbA(1c) in the 1993 cohort was significantly lower than that in the 1985 cohort. The largest decrease in HbA(1c) in NIDDM was in patients treated with insulin (9.53% +/- 2.0% versus 8.54% +/- 1.5% in 1985 and 1993, respectively, P = 0.004). Multiple linear regression analyses demonstrated that increased frequency of self-monitoring and of insulin injections were associated with lower HbA(1c) in IDDM. CONCLUSIONS: The level of average glycemia has decreased in IDDM patients over the past 8 years, attributable, at least in part, to an increased frequency of monitoring and of insulin injections. Glycemia decreased in NIDDM, especially in the subset of patients treated with insulin. This temporal shift in glycemic control should have a salutary effect on the development of long-term microvascular and neurologic complications.