Hematology and Heights – A Concern for People Living at High Altitude

Abstract Background: Hemoglobin (Hb) values are higher in people living at an altitude as compared to inhabitants living at sea level, therefore, to define anemia and polycythemia based on Hb cutoffs may be different in both areas. Kotagiri is a town and a hill station in the Nilgiris district, located at 1847 m above the mean sea level. Patients coming for treatment at a secondary-level hospital in Kotagiri, present with tiredness and being breathless even with a Hb of 10 g/dl, thereby postulating that the true prevalence of anemia may be underestimated if standard cutoffs are applied in high-altitude regions. Data regarding this are still insufficient and the use of standard cutoffs is still recommended. Hence, we wanted to evaluate complete blood counts (CBC) and peripheral smear findings in a cohort of normal adult healthy volunteers to determine the distribution of Hb levels and ascertain the prevalence of elevated Hb. Methodology: This was a prospective, observational cohort study over 1 year from April 2023 to March 2024 after approval from the ethics and research committee. The blood samples for CBC testing were obtained from 207 consenting healthy adults, both males and females aged between 18 and 60 years, who have been residing in the Nilgiris for a minimum of 6 months and who did not have any chronic illness, were nonsmokers and not on any medications. The samples were analyzed within 6 h of collection on a calibrated hematology analyzer and stained peripheral blood smears were reviewed. Data were tabulated using MS Excel ™ and analyzed using SPSS ™ V23. Results: The study included a total of 207 participants, of which 102 were males and 105 were females. The mean Hb in females was 12.64 g/dl (range: 9.46–15.82 g/dl) and in males was 15.73 g/dl (range: 12.05–19.41 g/dl). In this cohort, 34 (16.5%) participants had Hb > 16.5 g/dl; all were healthy adult males with no history of smoking, medication or chronic illness. We found 17 (8.2%) participants with hemoglobinopathy based on CBC parameters using the Mentzer index, and these were confirmed on high-performance liquid chromatography. Conclusion: This is the first time that an observational study is being done among people residing at an altitude in Nilgiris to demonstrate altitude-associated effect on the difference in levels of Hb between residents at sea level and those living at an altitude. The possibility of secondary polycythemia due to altitude needs to be studied. This also calls for revisiting reference intervals that define the normal.