Type 2 Diabetes (T2D) has emerged as a global concern, with its prevalence steadily increasing. The test of choice to diagnose and monitor T2D is hemoglobin A1c (HbA1c), which tracks average blood sugar levels over the last three months. Normal HbA1c levels are below 5.7%, 5.7% to 6.4% indicates prediabetes, and 6.5% or higher indicates diabetes. Within the prediabetes range, high HbA1c levels increase the risk of developing T2D. Additionally, levels above 6.5% correlate with greater risk for diabetes complications.1 Fasting Plasma Glucose (FPG) is an additional test that indicates an immediate blood sugar level following a period of fasting. Normal FPG levels are below 100 mg/dL (5.5 mmol/L), 100 to 125 mg/dL (5.6 to 6.9 mmol/L) suggests prediabetes, whereas 126 mg/dL (7 mmol/L) or higher generally indicates diabetes.2 Because HbA1c provides an overview of blood sugar levels spanning the past 2-3 months, it offers a more comprehensive insight into blood sugar management and is the preferred diagnostic test for T2D.3 Recent studies are unveiling discrepancies between HbA1c and glucose testing, prompting discussions on specific diagnostic criteria for different populations.
People living at high altitude experience unique physiological adaptations, such as higher hemoglobin levels and specific glucose metabolism patterns. Acknowledging these adaptations, a 2017 study by Bazo-Alvarez et. al sought to evaluate the relationship between HbA1c and FPG among individuals at sea level compared to those at high altitude.
The study analyzed data from 3613 Peruvian adults without diagnosed diabetes from both sea level and high altitude (>3000m). The mean values for hemoglobin, HbA1c, and FPG differed significantly between these populations. The correlation between HbA1c and FPG was quadratic at sea level but linear at high altitude, suggesting different glucose metabolism patterns. Additionally, for an HbA1c value of 48 mmol/mol (6.5%), corresponding mean FPG values were significantly different: 6.6 mmol/l at sea level versus 14.8 mmol/l at high altitude.
This significant difference in predictive values suggests potential controversy in utilizing HbA1c as a diagnostic tool for diabetes in high altitude settings. Using HbA1c at altitude potentially underdiagnoses and under treats patients. To ensure a more accurate diagnosis of T2D at high altitude, reevaluating diagnostic criteria, possibly leaning towards FPG or oral glucose tolerance testing (OGTT) might be necessary.
In conclusion, this study emphasizes the need for careful consideration when diagnosing diabetes in high-altitude regions. Future research is warranted, including studies replicating the findings of the cross-sectional study by Bazo-Alvarez and longitudinal studies exposing the long-term effects of the diagnostic discrepancy of HbA1c in high altitude patients. This additional data will ensure accurate diagnosis and appropriate management of diabetic patients at high altitude.
References
- Centers for Disease Control and Prevention. A1C Test. Accessed 12/26/23. Available from: https://www.cdc.gov/diabetes/managing/managing-blood-sugar/a1c.html
- World Health Organization. Fasting Blood Glucose. Accessed 12/26/23. Available from: https://www.who.int/data/gho/indicator-metadata-registry/imr-details/2380#:~:text=When%20fasting%20blood%20glucose%20is,separate%20tests%2C%20diabetes%20is%20diagnosed
- Sherwani, S.I., et al. 2016. Significance of HbA1c Test in Diagnosis and Prognosis of Diabetic Patients. Biomark. Insights. 2016 Jul; 11: 95-104. DOI: 10.4137/BMI.S38440.
- Bazo-Alvarez, J. C., et al. Glycated haemoglobin (HbA1c) and fasting plasma glucose relationships in sea-level and high-altitude settings. Diabet. Med. 2017 Jun; 34(6): 804-812. DOI: 10.1111/dme.13335.
Ambra Saurini is a second-year physician assistant student at Red Rocks Community College in Arvada, CO. She was born and raised in Denver, but Italian is her first language and she spent summers visiting her grandparents in Italy. She received her undergraduate degree in integrative physiology from the University of Colorado at Boulder. Before PA school, she worked as a research assistant in the Sleep and Development Lab at CU and as a medical assistant at Panorama Orthopedics and Spine Center. In her free time, she enjoys trying new restaurants and coffee shops, hiking, and spending time outside with her two-year old daughter, Chiara.
