Unexpectedly low hemoglobin A1c in a patient with chronic lymphocytic leukemia

Glycated hemoglobin (HbA1c) assays are currently utilized to monitor patients with diabetes mellitus type 2 (T2DM). These assays employ various methods, some of which are more prone to interference than others. Commonly recognized causes of interference include hemoglobin variants and conditions that result in reduced red blood cell survival such as hemolytic anemia and certain medications. Enzymatic assays represent one of the predominant methods for HbA1c testing for practical reasons. Herein, we describe a potentially novel interference in an enzymatic HbA1c assay by neoplastic lymphocytes in a patient with chronic lymphocytic leukemia. We hypothesize that the marked number of neoplastic lymphocytes are interfering in the enzymatic steps inherent to this assay, resulting in a discordantly low HbA1c result. Awareness of this possibility and further investigation into the precise mechanism by which this interference is occurring are warranted.