Extremely Low HbA1c Masking Glucose Intolerance in a Pregnant Woman with Autoimmune Hemolytic Anemia: A Case Report.

OBJECTIVE: Hemoglobin A1c (HbA1c) is unreliable in conditions shortening red blood cell (RBC) lifespan, such as autoimmune hemolytic anemia (AIHA). We report a rare case of extremely low HbA1c masking glucose intolerance in a pregnant woman. CASE REPORT: A 34-year-old woman at 20+2 weeks' gestation had HbA1c 2.02% (reference: 4.0-5.7%). A 75g Oral Glucose Tolerance Test (OGTT) confirmed gestational diabetes mellitus (GDM). Investigations revealed mild anemia, elevated reticulocytes, spherocytes, and positive IgG direct antiglobulin test (DAT), confirming AIHA. Both conditions were managed successfully; postpartum OGTT showed impaired glucose tolerance. CONCLUSION: AIHA-induced shortening of the RBC lifespan causes falsely low HbA1c. We suggest that an HbA1c level < 4.0% in pregnancy should serve as a clinical "red flag," necessitating immediate 75g OGTT and a comprehensive hematologic workup (e.g., CBC and DAT) to prevent the masking of GDM and ensure optimal maternal-fetal outcomes.