Influence of different methods for measuring HbA1c on health checkups in a rural town in Hokkaido, Japan.

Using data on health checkups performed in one Japanese town, we investigated the effect on health checkups of the methods used to measure hemoglobin A1c (HbA1c). The study included 337 participants undergoing health checkups at two facilities. At facility 1, HbA1c was measured by high-performance liquid chromatography (HPLC) in 2012 and by immunoassay (IA) in 2013, while at facility 2, HbA1c was measured by HPLC in both years. At facility 1, the mean HbA1c was significantly decreased from 2012 to 2013 (5.83 vs 5.50 %, respectively; P < 0.001), although the mean fasting plasma glucose (FPG) was significantly increased from 2012 to 2013 (91.7 vs 95.2 mg/dL, respectively; P = 0.02). Of the 202 participants at facility 1, 97 who had an HbA1c of ≥5.6 % in 2012 had an HbA1c of <5.6 % in 2013. At facility 2, the mean HbA1c marginally increased, while there were similar FPG levels in both years. An additional study of single blood samples from 27 healthy participants who were tested at the same facility using both HPLC and IA found that the mean HbA1c was significantly lower for IA than for HPLC (5.19 vs 5.50 %, respectively; P < 0.001). In summary, we found a substantial decrease in the mean HbA1c and the prevalence of impaired glucose tolerance and diabetes mellitus in study participants who underwent health checkups for two consecutive years when different methods were used to measure HbA1c. The lack of standardization of HbA1c measurement methods may have a large effect on health checkups.