Markedly Discordant and Rapidly Changing Hemoglobin A1c Values in a Normoglycemic Patient: A Case Report.

Hemoglobin A1c (HbA1c) reflects average glycemia over approximately two to three months and is widely used for the diagnosis and monitoring of diabetes mellitus; however, discordant results may occur due to analytical interference, altered erythrocyte turnover, or preanalytical factors. We report a 31-year-old male with no known history of diabetes who presented for routine laboratory evaluation and was found to have an HbA1c of 13.9% despite a normal fasting plasma glucose of 89 mg/dL. Repeat testing of the same sample six hours later demonstrated a decrease to 7.5%, and a simultaneously collected new sample yielded an identical value. Over subsequent days, repeated measurements across multiple samples showed further decline and eventual stabilization at 5.8%. The patient remained asymptomatic, and additional evaluation did not support persistent hyperglycemia. Urine toxicology screening was positive for opioids, and the patient reported recent use of an unidentified substance. A follow-up sample obtained after two weeks confirmed a stable HbA1c of 5.8%. The rapid intra-sample variability and subsequent normalization observed in this case are inconsistent with the known kinetics of hemoglobin glycation and strongly suggest a non-physiological mechanism, most likely assay interference. This case emphasizes the importance of verifying unexpected HbA1c results prior to clinical decision-making to avoid misdiagnosis and inappropriate management.