The value of HbA1c for diagnosis of abnormal glucose metabolism in highland dwellers with different hemoglobin levels

Objective To explore the discrepancy of HbA1c for diagnosis of diabetes mellitus and pre-diabetes in highland dwellers with different hemoglobin (Hb) level. Methods A total of 904 health volunteers living in Tibet altitude(average altitude is above 3 000 m) were recruited. Subjects were divided into three groups according to the Hb level: normal Hb group (n=460), high Hb group (n=332) and high altitude polycythemia (HAPC) group (n=112). Oral glucose tolerance tests (OGTT) with 75 g glucose was performed. Fasting blood glucose(FBG), 2-hour post-prandial blood glucose(2 hPG), HbA1c, blood routine and biochemical indexes were tested. Blood pressure, height and weight were measured.Based on criteria for diagnosis of abonormal glucose metabolism by WHO in 1999, receiver operating characteristic curves (ROC) were drawn to determine the optimal HbA1c diagnostic cut-off point, areas under the curves(AUC), specificity, sensitivity of diabetes and pre-diabetes status respectively in highland dwellers with different Hb levels. Results Among normal Hb group, high Hb group and HAPC group, the best threshold of HbA1c for detecting diabetes was 6.1%, 6.5% and 7.1% respectively, the AUC for detecting diabetes was 0.96, 0.91 and 0.74 respectively, the specificity for detecting diabetes was 0.94, 0.90 and 0.82 respectively, the sensitivity for detecting diabetes was 0.87, 0.82 and 0.57 respectively. The best threshold of HbA1c for detecting pre-diabetes was 5.8%, 5.9% and 6.2% respectively, the AUC for detecting pre-diabetes was 0.73, 0.72 and 0.61 respectively, the specificity for detecting pre-diabetes was 0.77, 0.68 and 0.57 respectively, the sensitivity for detecting pre-diabetes was 0.59, 0.68 and 0.67 respectively. Conclusion The cut-off point of HbA1c detecting diabetes elevates with the increase of Hb level. HbA1c may not be suitable for diagnosing diabetes or pre-diabetes in HAPC population.