Changes in Coagulation Factors at High Altitude: A Systematic Review

Background: The numbers of individuals age 50 and over who maintain active lifestyles is growing. Many of these individuals travel to or live at, higher altitudes, to pursue outdoor activities or travel to higher altitudes for business. The use of anticoagulant therapy has continued to increase over the past two decades among individuals 50 and over. Warfarin is effective but requires a narrow therapeutic range based on the International Normalized Ratio (INR). Clinicians have concerns as to whether, ascending to higher altitudes, affects coagulation parameters and INR in warfarin patients. Methods: A comprehensive search was conducted using Medline, CINAHL, Web of Science, Pubmed, and EBMR multifile. Three studies were chosen based on relevance to the topic. Each study was evaluated using GRADE criteria. Results: Results from all three studies show that increase in altitude changes coagulation parameters indicating of a hypercoagulable state. A retrospective chart review determined that warfarin patients traveling to an altitude of 2400m had a significantly increased risk of subtherapeutic INR. An observational study on a high altitude expedition showed changes in coagulation parameters resulting in hypercoagulation. A cohort study of subjects ascending to high altitude also showed tendency towards a thrombotic state, especially an increase in fibrinolysis inhibitors, platelets and hemoglobin. Conclusion: The studies show that altitude can change coagulation parameters which contribute to a hypercoagulable state and could decrease INRs of warfarinized patients in whom ascending to altitude increases the risk of thrombosis. The body of evidence was rated as low according to GRADE guidelines.