Glycohemoglobin Results in Samples with Hemoglobin C or S Trait: A Comparison of Four Test Systems

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Abstract
A wide variety of commercial methods are available to measure glycohemoglobin (gHb). These methods measure various species of gHb, e.g., total gHb, hemoglobin A1 (Hb A1), or Hb A1c. Some methods are based on charge differences between glycated and nonglycated hemoglobins (e.g., cation-exchange chromatography, electrophoresis, and isoelectric focusing), whereas boronate affinity methods depend upon the binding of the sugar groups on the hemoglobin molecule (1). Immunoassay of Hb A1c depends on the presence of an epitope that includes glucose and N-terminal amino acids of the β chain of hemoglobin. These methods usually measure Hb A1c as a percentage of total hemoglobin. Some immunoassay methods also measure Hb S1c or Hb C1c, whereas others do not (2). The National Glycohemoglobin Standardization Program (NGSP) was established to certify the various commercial methods so that they can be related to the candidate reference method used in the Diabetes Control and Complications Trial (DCCT) (3)(4).