High Variability of Glycated Hemoglobin Concentrations in Patients With IDDM Followed Over 9 years: What is the best index of long-term glycemic control?

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Abstract
OBJECTIVE: To determine variability of long-term glycemic control in patients with IDDM. RESEARCH DESIGN AND METHODS: A retrospective analysis of HbA1 among 122 IDDM patients followed over 9 years. RESULTS: Annual group mean HbA1 ranged from 8.4 to 9.3% with large standard deviations (1.7–2.0%), indicating marked variability among individuals. Fluctuations of more than ± 1% HbA1 occurred in 50% of the patients year to year, and over 9 years the minimum-maximum range was > 3 and > 5% HbA1 in 55 and 11% of patients, respectively. In any one year, 22–43% of patients had HbA1 < 8%, but over 9 years only 3.3% were consistently < 8%. Groups divided according to baseline HbA1 of < 8, 8–10, and > 10% were significantly separated over 9 years by frequency distribution analysis of individual mean HbA1 but were indistinguishable when analyzed by individual HbA1 interquartile range (measure of variability). CONCLUSIONS: High variability of long-term glycemic control is a marked feature of IDDM, the extent of which may be relevant to microvascular risk.