Glycated hemoglobin (HbA1c) is used to monitor the long-term management of diabetes and reflects the average blood glucose level over the past three months. Hb J is an alphaglobin gene variant that occurs less commonly but can interfere with the HbA1c result. This case report presents two cases of abnormally high HbA1c in patients with Hb J using the high-performance liquid chromatography (HPLC) method and repeated value using the capillary electrophoresis (CE) method. The first case was a 26 years old female Malay patient, presenting at 25 weeks gestation with diabetes mellitus (DM). Her HbA1c results from HPLC showed persistently high level (> 18.5%, > 179 mmol/mol) despite optimum diabetic control (fasting blood sugar (FBS) range 4.0–6.1 mmol/L). The second case was a 62-year-old female Malay with type 2 DM. Her HbA1c results from HPLC was also persistently high (> 18.5%, > 1;79 mmol/mol) despite good diabetic control (FBS average 5.0–7.0 mmol/L). Both patients' hemoglobin analysis reports were suggestive of Hb J. Repeated HbA1c using CE were 6.0% (42 mmol/mol) and 8.1% (65 mmol/mol), respectively, and supported the presence of the Hb J variant peak. HbA1c measurement in patients with a variant should be interpreted with caution to avoid misdiagnosis and mismanagement in these kinds of patients.