The effect of high altitude on platelet counts, thrombopoietin and erythropoietin levels in young Bolivian airmen visiting the Andes

Recognition of thrombosis as a complication of exposure to high altitude ha s stimulated interest in rheological changes resulting from hypobaric hypox ia. Previous studies of platelet counts at high altitude have yielded confl icting results and have not been studied in conjunction with potential medi ating cytokines. We studied the effects of high-altitude exposure on platel et numbers, thrombopoietin (tpo) and erythropoietin (epo) levels in man. A group of 28 volunteers from the Bolivian Airforce stationed at Santa Cruz ( 600 m altitude) were studied 48 h and 1 week; after their ascent to La Pat (3600 m). In addition 105 volunteers based at Santa Cruz for at least 1 yea r were compared with 175 age- and sex-matched residents at Fl Alto (4200 m) . Platelet counts were measured immediately after sampling and serum sample s assayed for tpo and epo. In the ascending group, mean platelet counts wer e 251x10(9), 367x10(9) and 398x10(9)/l at 600 m and following 48 h and 1 we ek at 3600 m respectively. Mean tpo levels were 132.5, 76 and 92 pg/ml with epo values of 2.98, 11.6 and 7.9 mIU/ml respectively. In the resident popu lations mean platelet counts were 271x10(9)/l in the low- and 471x10(9)/l i n the high-altitude groups. Mean tpo and epo levels measured 69.3 pg/ml and 4.5 mIU/ml respectively at 600 m and 58.5 pg/ml and 5.1 mIU/ml at 4200 m. In conclusion we have demonstrated a significant and sustained elevation in platelet numbers within 48 h of ascent to high altitude. Our findings do n ot support a role for tpo as a mediator of the increased platelet count. Ho wever, these data do not discount epo as a potential candidate.