Interference With Hemoglobin A1cDetermination by the Hemoglobin Variant Shelby

Hemoglobin variant carrier status was found in a 46-year-old African American man following detection of a falsely elevated hemoglobin A1c (HbA1c) by ionexchange high-performance liquid chromatography (HPLC, VARIANT A1c, Bio-Rad Laboratories, Hercules, CA). Additional analysis of the hemoglobin variant using the Beta Thal Short program (Bio-Rad) revealed an unknown peak with a retention time of 4.84 minutes and a proportion of 26.3%. No mass shift in alpha-globin or beta-globin proteins was observed by mass spectrometry. DNA sequencing revealed a missense mutation in 1 beta-globin allele corresponding to the hemoglobin Shelby trait. The patient was asymptomatic with a normal hemoglobin value of 13.6 g/dL (136 g/L) but had increased target cells on a peripheral blood smear. An alternative method for HbA1c determination using boronate-affinity HPLC provided a value of 3.9% (0.04; reference range, 4.0%-6.9% [0.04-0.07]), more consistent with the patient's recent blood glucose values in the normal range.