Unintended reporting of misleading Hb A(1c) values when using assays incapable of detecting hemoglobin variants

It is recommended that hemoglobin (Hb) A1c (Hb A1c) not be used to assess average glycemia in patients who have altered red blood cell life span.

To investigate the frequency of reporting an Hb A1c value for Hb variant samples that do not include Hb A.

Hb A1c samples (n = 500) were procured and screened for Hb variants that may affect Hb A1c interpretation (Hb SS, Hb SC, and Hb S-β-thalassemia). Five of each of these samples were tested by ion-exchange high-performance liquid chromatography, immunoturbidimetric assay, second-generation immunoturbidimetric assay, and affinity chromatography.

Eleven (2.2%) homozygous Hb SS, 6 (1.2%) Hb SC, and 5 (1.0%) Hb S-β-thalassemia samples were identified out of the 500 samples tested. Three of 4 instruments investigated in this study are known to not be plagued by analytic interference from these Hb variants but disturbingly reported Hb A1c values in the absence of Hb A.

The improved analytic specificity of Hb A1c platforms has by and large eliminated interferences from the most common heterozygous Hb variants. A consequence, however, is the potential for unintended reporting of Hb A1c results in the presence of homozygous and compound heterozygous Hb variants that lack Hb A and the inability to distinguish those samples not recommended to be used for patient care. The ability to identify samples harboring Hb variants that preclude the utility of Hb A1c may be beneficial in high prevalence populations.