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

To determine variability of long-term glycemic control in patients with IDDM.

A retrospective analysis of HbA₁ among 122 IDDM patients followed over 9 years.

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).

High variability of long-term glycemic control is a marked feature of IDDM, the extent of which may be relevant to microvascular risk.