Long-term haematological adaptation in native populations across different level of altitude

Background: The long-term haematological adaptations to hypobaric hypoxia (decrease in plasma volume and increase in haematocrit, number of red blood cells and haemoglobin) have been widely studied in people living at high altitudes (>4000 m a.s.l.), but few studies have been performed at lower altitudes. However, about the 26.3% of the world population live at altitude higher than 500 m a.s.l.(1). Moreover, few data are available on the dynamics of erythropoietic stimulus across different altitudes, whereas literature data focused mainly on natives at very high altitude (i.e. > 3500 m a.s.l.) (2,3). Therefore, the aim of this study was to analyse the chronic haematological adaptation at low-to-moderate altitudes (250-3100 m) and to describe the relationship between haematological parameters and altitude. Material & Methods: Red blood cells number (RBC: 10^6/mm^3), haemoglobin concentration (Hb, g/dL) and haematocrit (Hct, %) were analysed in 510 subjects (M/F 281/223; age 15-59 years) living between 250 and 3100 m a.s.l. Analyses were performed with Advia 120 Hematology System (Bayer HealthCare, NY). Moreover, we collected literature data for the same parameters in people resident in areas above 3100 m. The relationship between altitude and haematological parameters was evaluated by a simple linear regression analysis. The maximal value of the standard error of the regression between altitude and each biohumoral parameter was used to define the point of maximal slope change in regression lines, using a point-by-point running algorhythm. Results: All parameters showed a significant positive correlation with altitude in both males and females. In males, from 250 to 3150 m: RBC=+9.8% (mean variation=0.34% per 100 m); Hb=+6,5m (0.22% per 100 m); Hct +5.2%, (0.18% per 100 m). In females, from 250 to 1815 m: RBC=+2.8% (0.22% per 100m); Hb=+1.6% (0.06% per 100 m); Hct=+2.1% (0.07 per 100 m). Unexpectedly, by integrating the present data with similar literature data on healthy subject living at higher altitudes, we found a slope increase of all these relationships around 3200-3400 m. Discussion & Conclusions: Although at low-to-moderate altitudes, significant positive linear relationships between altitude level and RBC, Hb and Hct in residential populations were observed, suggesting that the erythropoietic stimulus begins at very low altitudes and continues linearly with quote. However, peoples living above 3200 m seems to show a higher erythropoietic response to increasing altitude, suggesting that other possible mechanisms (progressive chronic hypohydration? Central response to hypoxia? Others?) may contribute to strengthen such stimulus. References: (1) Cohen JE ; C Small Hypsographic demography: The distribution of human population by altitude Applied Physical Sciences, Social Sciences 1998 Vol. 95, pp. 14009–14014, ; (2) Windsor JS, George WR. Heights and haematology: the story of haemoglobin at altitude Postgrad Med J 2007;83:148–151 ; (3) Beall CM. Two routes to functional adaptation: Tibetan and Andean high-altitude natives. Proc Natl Acad Sci U S A. 2007 May 15;104 Suppl 1:8655-60.