Acclimatized Lowlanders Exhibit a Hypocoagulable Profile after a Passive Ascent at High Altitude

Stauffer, Emeric, François Caton, Raphael Marlu, Aurélien Pichon, Landry Seyve, Michael Furian, Aymeric Paillisser, Florence Berquet, Jeremy De Abreu, Blandine Deschamps, Benoit Polack, Philippe Connes, Paul Robach, Stéphane Doutreleau, Julien V. Brugniaux, Samuel Verges, and Benoit Champigneulle. Acclimatized lowlanders exhibit a hypocoagulable profile after a passive ascent at high altitude. High Alt Med Biol. 26:209-214, 2025. Background: Discordant results have been previously reported regarding the impact of high-altitude (HA) exposure on coagulation. We aimed to investigate changes in coagulation parameters in lowlanders exposed to HA for 14 days using a combination of dynamic coagulation assays and conventional in vitro tests. Material and Methods: We assessed coagulation in 10 lowlanders using whole-blood rotational thromboelastometry (ROTEM), thrombin generation assay (TGA) on poor-platelet plasma, and conventional coagulation tests. Tests were performed at low altitude (LA, 210 m) and at the end of a 14-day sojourn at HA, including passive ascents to 3,800 m for 6 days and then to 5,100 m for 8 days. Results: Conventional tests revealed significant changes in coagulation factors and inhibitors after HA exposure, although these changes remained within normal ranges. ROTEM assays demonstrated a delayed clot initiation in EXTEM/FIBTEM, without any alteration in clot firmness, in HA versus LA (p < 0.01). TGA changes showed an increase in time to peak (p < 0.01), a decrease in endogenous thrombin potential (p < 0.05), and a decrease in thrombin peak (p < 0.001). Conclusions: We found no evidence of hypercoagulability in lowlanders after a 14-day sojourn at HA. In contrast, dynamic coagulation assays (ROTEM and TGA) revealed a hypocoagulable pattern.