Effect of Long-Term Monitoring of Glycosylated Hemoglobin Levels in Insulin-Dependent Diabetes Mellitus

BACKGROUND: The value of routine measurements of glycosylated hemoglobin (hemoglobin A1c) in the care of patients with diabetes mellitus is uncertain. We undertook this study to determine whether knowledge of hemoglobin A1c values would result in improved metabolic control in a group of patients with insulin-dependent diabetes mellitus (IDDM). METHODS: We randomly assigned 240 patients with IDDM to one of two groups that were comparable in age, sex, duration of diabetes, and initial hemoglobin A1c levels. The patients were followed for a year, and the hemoglobin A1c concentration was measured at three-month intervals. The hemoglobin A1c values were used in assessing glycemic control and modifying therapy in one of the two groups. In the other, care givers were not aware of the hemoglobin A1c levels and relied on blood or urine glucose measurements to monitor treatment. RESULTS: Among the 222 patients still being followed after one year, the mean hemoglobin A1c value decreased significantly--from 10.1 to 9.5 percent (P less than 0.005)--in the group whose hemoglobin A1c level was monitored (n = 115), whereas the initial and one-year values in the control group (n = 107) were 10.0 and 10.1 percent, respectively. The proportion of patients with poor control, defined as those having a hemoglobin A1c value above 10.0 percent, decreased from 46 to 30 percent (P less than 0.01) in the group whose hemoglobin A1c level was monitored but did not change significantly (45 to 50 percent) in the control group. The patients in the group whose hemoglobin A1c level was monitored were seen and their insulin regimens changed more often, but they were hospitalized for acute care of their diabetes less often than those in the control group. A similar decrease in hemoglobin A1c values occurred in the control group in the following year, when their care givers knew their hemoglobin A1c values. CONCLUSIONS: Regular measurements of hemoglobin A1c lead to changes in diabetes treatment and improvement of metabolic control, indicated by a lowering of hemoglobin A1c values.