ABSTRACT Objective: Earlier cases have documented a discrepancy between glycated hemoglobin A1c (HbA1C) levels and glycemic control in patients with diabetes and previously diagnosed hereditary spherocytosis (HS). However, this has not been reported in patients with normal hemoglobin (Hb) and red blood cell (RBC) indices. Methods: A 22-year-old Caucasian woman with type 1 diabetes since age 11 was referred to Endocrinology for persistent hyperglycemia. Results: The initial HbA1C was 5.1% with normal Hb, hematocrit, mean cell volume, mean corpuscular Hb concentration, and RBC distribution. Given self-reported hyperglycemia, fructosamine was checked and was elevated (358 μmol/L, normal [nl] 200–285 μmol/L). Peripheral smear was normal. Professional retrospective continuous glucose monitoring (CGM) demonstrated marked hyperglycemic excursions, particularly in the evenings, with mean sensor glucose of 195 mg/dL ± 48, corresponding HbA1C of 5.5%, and fructosamine of 370 μmol/L. She later reported new diagnosis...