A Case of Hb Phnom Penh Showing Different HbA1c Levels Depending on the High-Performance Liquid Chromatography System

The case of a 49-year-old man with Hb Phnom Penh whose HbA1c levels varied depending on the high-performance liquid chromatography (HPLC) system is presented. After the results of a health checkup showed a high HbA1c level of 7.6% measured by HPLC method, another HbA1c test measured by immunoassay at a local clinic showed a level of 5.2%. Given the discrepancy in HbA1c levels between assay methods, he visited our clinic. His fasting plasma glucose level was 95 mg/dL, but an oral glucose tolerance test showed diabetes mellitus. The mean plasma glucose level was 117 mg/dL on intermittently scanned continuous glucose monitoring (isCGM), giving an estimated HbA1c level of 5.9%. Based on the results of isCGM, the present case was considered to be not diabetes mellitus. The same specimen was assayed for HbA1c by various methods (systems), including HPLC with Tosoh G9, HPLC with Arkray HA-8180 and HA-8180T, affinity assay, and enzymatic assay, giving HbA1c levels of 7.3%, 4.9%, 5.0%, 5.4%, and 5.3%, respectively. A globin gene analysis diagnosed Hb Phnom Penh (α1-117Phe-Ile-α1-118Thr). The present case had a unique hemoglobin variant, resulting in high HbA1c levels when measured with Tosoh's HPLC systems and low HbA1c levels with Arkray's HPLC systems.