Intraindividual variation of glycohemoglobin: implications for interpretation and analytical goals

Intraindividual variation (CVi) for glycohemoglobin (GHb) was estimated from serial measurements in patients with diabetes in either stable or variable clinical control. GHb determinations were performed by an affinity column procedure with an analytical imprecision of 4.9% (weighted average; GHb 8.2-14.7%). Within the groups of patients, both a short- (28-32 days) and long-term (approximately 85 days) sampling protocol was used. The derived CVi for each category was 4.2% (n = 16, stable, short-term), 7.1% (n = 23, stable, long-term), 5.1% (n = 13, variable, short-term), and 9.8% (n = 21, variable, long-term). The mean GHb within each category was similar (approximately 11%), and there was no statistically significant difference in GHb values between categories. The results establish that the CVi for GHb is affected by both clinical control and the sampling time interval. These findings have important implications for the estimation of significant differences between serial GHb measurements and the setting of appropriate analytical precision goals.