Incomplete Removal of Labile Fraction When Measuring Hemoglobin A1c with Bio-Rad Variant® Analyzer

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Abstract
When glucose reacts with hemoglobin (Hb), the first products are Schiff bases that slowly undergo Amadori rearrangement to produce stable ketoamines (glycohemoglobin). The relative fraction of the ketoamines to total Hb can be measured as hemoglobin A1c (Hb A1c), which constitutes ∼60% of the bound glucose (1). The Schiff base (or labile fraction) is unstable and is fairly readily hydrolyzed, especially at acid pH. Effective removal of the labile fraction is essential for the accurate determination of Hb A1c because the labile fraction cannot be separated from the true (ketoamine) fraction by simple ion-exchange procedures and because its concentration varies acutely with the plasma glucose concentration .(2). Partial and variable removal of the labile fraction adds to assay imprecision and reduces the correlation (3) between measured Hb A1c and mean plasma glucose.