Erythrocytosis and Performance of HbA1c in Detecting Diabetes on an Oxygen-Deficient Plateau: A Population-based Study.

CONTEXT: The hemoglobin A1c (HbA1c) test is a standard test for diabetes screening and diagnosis. OBJECTIVE: To evaluate A1c performance for diabetes screening in high-altitude polycythemia compared to a population with a high proportion of people living in an oxygen-deficient environment. DESIGN: A population-based epidemiological survey was conducted. SETTING: The cities Lhasa and Shigatse were selected. Volunteers were recruited through educational advertisements about diabetes. PARTICIPANTS: A total of 1401 Tibetan adults without known diabetes. INTERVENTIONS: Oral glucose tolerance test (OGTT), HbA1c, and complete blood cell count were performed. Hemoglobin A1c was evaluated using high-performance liquid chromatography, and serum glucose level, using the hexokinase method. MAIN OUTCOME MEASURES: World Health Organization criteria were used to define diabetes and prediabetes. Hemoglobin A1c test performance was evaluated using receiver operating characteristic analysis. RESULTS: The participants' mean age was 44.3 ± 15.0 years; 33.3% of the participants were men and 38.6% lived in urban areas. The prediabetes and diabetes prevalence rates were 7.5% and 3.6%, respectively. The optimal HbA1c cutoff for detecting diabetes was 46 mmol/mol (6.4%), with a sensitivity and specificity of 60.8% and 93.6%, respectively. The cutoff for detecting diabetes was 6.7% (50 mmol/mol) in subjects with high-altitude polycythemia (HAPC). The relationship between red blood cell (RBC) counts and HbA1c was significant (P < 0.001), while there was no correlation between hemoglobin (Hb) and HbA1c (P = 0.085). Multiple linear regression analysis showed that after adjusting for age and fasting serum glucose or 2-hour OGTT (OGTT2h) serum glucose, RBC count and not Hb level was an independent risk factor for HbA1c (ß = 0.140, P < 0.001). CONCLUSIONS: The optimal HbA1c cutoff for detecting diabetes was 46 mmol/mol (6.4%) in Tibet. Red blood cell count was an independent risk factor for elevated HbA1c, and HAPC may affect the predictive ability of HbA1c.

Safety of Metformin Therapy in Patients with Type 2 Diabetes Living on an Oxygen-Deficient Plateau, Tibet, China.

BACKGROUND: In the general population, the absolute risk of lactic acidosis in patients treated with metformin appears to be low. However, in the Tibetan plateau, an extreme oxygen-deficient environment, there are no data available concerning the safety of metformin. The aim of our study is to assess the safety of metformin in people of the plateau area. METHODS: We conducted an observational cross-sectional study in Tibet. All the 166 subjects were divided into two groups: T2DM+metformin group and T2DM group. Clinical characteristics as well as lactate levels were measured in all subjects. The association between lactate, metformin use, FBG, HbA1c, eGFR, and other potential predictors was evaluated. RESULTS: A total of 166 subjects were enrolled in this study. Average age was 51.7±12.3 years, and the percentage of male participants was 67%. The median level of lactate was 1.89 (1.35-2.91) mmol/L in all the subjects. The mean (±SD) lactate concentration in patients treated with metformin, versus those who were not, was 2.35±1.42 vs 2.29±1.65 mmol/L, respectively (mean difference 0.06 mmol/L, 95% CI: -0.48-0.60, P=0.556). FBG was significantly higher in the high lactate group than in the low lactate group (12.1±4.1 vs. 10.5±4.0 mmol/L, P=0.018). Similarly, HbA1c level was also significantly higher in the high lactate group than in the low lactate group (12.3±2.6 vs. 11.0±3.0%, P=0.008). CONCLUSIONS: In the oxygen-deficient Tibetan plateau, lactate concentration among patients on metformin was not significantly different from patients without metformin. The level of lactate was significantly associated with FBG and HbA1c levels.