Pathology Consultation on HbA1c Methods and Interferences

Abstract

Familiarity with the advantages and challenges of the various methods used for HbA1c testing is essential when establishing therapeutic management and goals based on HbA1c results, especially in populations with a high prevalence of Hb variants.

Unexpected laboratory results in cold agglutinin disease

“…According to previous and current glucose levels, the patient was considered to have impaired fasting glycemia. The reasons for interference in HbA1c measurement may be a shortened red blood cell lifespan, the presence of variant hemoglobin, uremia, or drugs [10,11]. There was no evidence of active hemolysis or uremia in this patient.…”

Detection of hemoglobin variant HbS on the basis of discrepant HbA1c values in different measurement methods

“…To date, four basic methods are available to measure HbA1c: immunoassay (immunonephelometry), ion-exchange HPLC, boronate affinity chromatography, and enzymatic assay [3]. Methods for detecting HbA1c are subject to interference by, for example, chemical structure and/or molecular charge, potentially resulting in inaccurate HbA1c measurements [5][6][7][8].…”

“…HBB mutations in certain hemoglobinopathies give rise to changes in the Hb b amino acid sequence that result in an altered charge state and in turn to incorrect measurements of HbA1c by HPLC [9]. Immunonephelometry measures inhibition of latex agglutination by antibodies that recognize the N-terminal glycated amino acids [3]. First-generation antibodies recognize amino acids 4-10 on the b chain of Hb, resulting in analytic interference by the globally prevalent HbS and HbC chains, in addition to other Hb variants that may span this epitope [3].…”

“…HbA1c is characterized by irreversible nonenzymatic glycation at the NH 2 moieties of valine residues in the hemoglobin (Hb) b chain, encoded by the HBB gene [2,3]. The accuracy of HbA1c measurement as a marker of hyperglycemia can be affected adversely by the presence of Hb variants that reduce red blood cell viability [3][4][5]. These variants are occasionally detected on the basis of discrepancies between actual plasma glucose levels and HbA1c values that arise due to a reduction in exposure of Hb to plasma glucose.…”

“…These variants are occasionally detected on the basis of discrepancies between actual plasma glucose levels and HbA1c values that arise due to a reduction in exposure of Hb to plasma glucose. Moreover, the altered electrophoretic mobility of certain Hb variants can give rise to artifacts in the measurement of HbA1c using high-performance liquid chromatography (HPLC) [3,[5][6][7][8][9]. Here we report an African patient with diabetes in whom an Hb variant was incidentally detected on the basis of a discrepancy between HbA1c values measured by HPLC and immunonephelometry.…”