Abstract: Objective To investigate the patterns and characteristics of hemoglobin (Hb) levels in different populations under high-altitude hypoxic conditions. Methods This study included 263 healthy adults divided into three groups: (1) Native Tibetan group (n=160): aged 18~65 (mean 38.3±13.0) years, residing at≥3 000 meters; (2) Long-term high-altitude Han Chinese group (n=50): aged 18~65 (41.0±7.5) years, residing at≥3 000 meters for≥10 years; (3) Acute High-Altitude Group (n=53): Age 18~36 (23.9±4.4) years, long-term residence in lowland areas (baseline altitude≤50 meters, mean 43.5 meters) with no prior high-altitude exposure. The native and long-term resident groups underwent a single cross-sectional assessment at their high-altitude locations. The Rapid Altitude Group employed a longitudinal study design: baseline measurements were taken at low altitude one week prior to high-altitude exposure (≥3 000 m), with repeated measurements conducted on days 3, 7 and 30 post-exposure. Statistical analysis of complete blood counts compared Hb levels between native Tibetans and long-term Han residents under identical high-altitude steady-state conditions to elucidate the influence of genetic factors on Hb homeostasis regulation. Hb levels were compared between baseline (lowland) and various high-altitude time points to observe acute mountain sickness and early acclimatization processes. Results 1) Hb levels in both male and female indigenous Tibetans were lower than those in long-term high-altitude Han Chinese [Males: (177±24) g/L vs. (203±23) g/L, P<0.01; females: (143±21) g/L vs. (156±24) g/L, P<0.05]; 2) The mean hemoglobin (Hb) level of Tibetan on the plateau in the 18~50-year-old age group was significantly lower than that of Han Chinese who had lived on the plateau for a long time [18~30 years: (157±26) g/L vs. (187±18) g/L, P=0.023; 30~40 years: (153±30) g/L vs. (178±33) g/L, P=0.003; 40~50 years: (156±33) vs. (178±36) g/L, P=0.022). Hemoglobin levels among Tibetan populations permanently residing at high altitudes were concentrated in the ranges of 140~150 g/L (20.63%) and 160~170 g/L (14.38%); among Han populations long-term residing at high altitudes, extremely high hemoglobin values (>200 g/L) accounted for 22%. 3) Hb levels in acutely acclimated populations exhibited a increase with time spent at altitude (7-day mean: 170 vs. baseline 152 g/L, Δ+11.2% increase at 7 days, Δ+4.7% at 30 days, P<0.001). Conclusion Hemoglobin levels serve as a sensitive physiological indicator of high-altitude adaptation across different populations, exhibiting polymorphic distribution patterns among distinct groups.

Key words: Hemoglobin, Plateau, Hypoxia, Hypoxic physiology, Sudden high-altitude ascent