Glycosylated Hemoglobin and Fasting Plasma Glucose in the Assessment of Outpatient Glycemic Control in NIDDM

Interpreting measurements of fasting plasma glucose (FPG) and glycosylated hemoglobin (GHb) is subject to inherent limitations. The time course of change in GHb cannot be reliably specified in the individual patient, nor do single measurements of GHb convey any information regarding recent change or stability in glycemic control. To evaluate whether the clinical utility of these measurements may be extended, sequential measurements of FPG and GHb were examined from 16 outpatients with NIDDM followed over periods of 12 successive weeks or longer, including intervals following cessation of prior therapy or initiation of new hypoglycemic therapy with glipizide. In some individuals as well as groups of patients, changes in GHb followed patterns previously described by mean changes among groups of patients. Differing from those patterns, however, other individuals demonstrated prompt improvement in GHb following substantial improvement in FPG, confirming that patterns of change described from group means do not apply to all circumstances of changing glycemic control, though they may represent the most common. By using measurements of both FPG and GHb obtained on a single occasion to calculate a third parameter, called the glycosylated hemoglobin index (GHb-1), accurate information could be obtained regarding changes in glycemic control which occurred over intervals of 1–4 wk prior to the measurements. By this approach the utility of GHb measurements in the management of outpatients with NIDDM may be extended beyond retrospective description of the “average” prior metabolic control to include assessment of recent changes in glycemia, either deterioration or improvement.