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Hemoglobin A1c (HbA1c) measurement is commonly performed in diabetes mellitus patients to monitor glycemic control over the last three to four months. Carbamylated hemoglobin, which is the hemoglobin that binds to isocyanic acid derived from urea, is one of the possible analytical interference in the uremic patient. When measured by ion-exchange high-performance liquid chromatography (HPLC), carbamylated hemoglobin forms a peak that overlaps the peak of HbA1c, causing a falsely elevated HbA1c result. We report a case of a 60-years-old man who had a spurious increase in HbA1c, with a high carbamylated hemoglobin peak disproportionate to the urea value. Subsequent hemoglobin analysis using hemoglobin electrophoresis and HPLC hemoglobin testing system suggested hemoglobin J (Hb J) variant. Our case highlighted the possibility of misleading HbA1c interpretation in the presence of a high carbamylated hemoglobin peak, but not proportionate to urea value. In this study, Hb J was detected. A method free from hemoglobin variant interference should be used ideally, and monitoring glycemic control should be performed using alternative methods, such as serum fructosamine or continuous glucose monitoring.