Glycated haemoglobin (HbA(1c)) and fasting plasma glucose relationships in sea‐level and high‐altitude settings

AIM: Higher haemoglobin levels and differences in glucose metabolism have been reported among high‐altitude residents, which may influence the diagnostic performance of HbA(1c). This study explores the relationship between HbA(1c) and fasting plasma glucose (FPG) in populations living at sea level and at an altitude of > 3000 m. METHODS: Data from 3613 Peruvian adults without a known diagnosis of diabetes from sea‐level and high‐altitude settings were evaluated. Linear, quadratic and cubic regression models were performed adjusting for potential confounders. Receiver operating characteristic (ROC) curves were constructed and concordance between HbA(1c) and FPG was assessed using a Kappa index. RESULTS: At sea level and high altitude, means were 13.5 and 16.7 g/dl (P > 0.05) for haemoglobin level; 41 and 40 mmol/mol (5.9% and 5.8%; P < 0.01) for HbA(1c); and 5.8 and 5.1 mmol/l (105 and 91.3 mg/dl; P < 0.001) for FPG, respectively. The adjusted relationship between HbA(1c) and FPG was quadratic at sea level and linear at high altitude. Adjusted models showed that, to predict an HbA(1c) value of 48 mmol/mol (6.5%), the corresponding mean FPG values at sea level and high altitude were 6.6 and 14.8 mmol/l (120 and 266 mg/dl), respectively. An HbA(1c) cut‐off of 48 mmol/mol (6.5%) had a sensitivity for high FPG of 87.3% (95% confidence interval (95% CI) 76.5 to 94.4) at sea level and 40.9% (95% CI 20.7 to 63.6) at high altitude. CONCLUSION: The relationship between HbA(1c) and FPG is less clear at high altitude than at sea level. Caution is warranted when using HbA(1c) to diagnose diabetes mellitus in this setting.