Warfarin Institute of America
DEDICATED TO YOUR HEALTH SINCE 2000
What is the Relationship Between Altitude and Warfarin?
Prepared by: Sara K. Singh, PharmD Candidate
University of Colorado School of Pharmacy
What are the effects of altitude change on warfarin?
-There has been an increased risk between clotting and traveling to altitude observed for a long time, but little is known about the effects of altitude on warfarin or INRs. A recent study, Risk of Impaired Coagulation in Warfarin Patients Ascending to Altitude, by Tissot van Patot, et al. evaluated the effect of travel to and from altitude on INRs in people taking warfarin. The study found an increased chance (2.7 fold) of having a lower than desired INR following recent ascent to altitude. Additionally, a 5.6 fold increase of having a low INR if a patient had atrial fibrillation and had recently ascended to altitude compared to those without a. fib or recent travel was reported. The study found a mean decrease of 0.7 points in INR in this group. The study defined altitude as greater than 2400 meters or 7200 feet.
Why would altitude affect my INR?
-It is not known why altitude may affect warfarin. It could be related to lower oxygen intake, changes in your body’s metabolism or a change in your body’s coagulation processes. Attempts to validate these hypotheses have not been successful, and this is complicated by the difficulty of assessing these factors because their effects on healthy people may differ from their effects on those patients taking warfarin.
What does this mean to me?
-It is too early to say much definitive regarding the relationship between ascent to altitude and INRs. This study only looked at 49 patients who all went to the same clinic and all lived at high altitude. The study also has some design characteristics that make a causative relationship difficult, including the fact that it was done retrospectively (looking back) rather than prospectively and that the affects of altitude was not the primary objective of the study. There are also some variables associated with travel, such as changes in nutritional and alcohol intake that could complicate the results. It remains to be seen how this data differs for people who do not live at altitude and whose bodies are therefore less accustomed to being at a high elevation. It is also notable that the elevation used in the study is considerably higher than that of Pueblo, where this clinic is located, or many of the other populated areas of Colorado. With the results of this study available, it may be advisable to have your INR checked shortly after traveling to altitude or returning home from lower elevations, especially if you have a.fib. Additional studies would need to be done that corroborate and clarify the observations of this study before that could be considered a solid recommendation however.
Some Colorado elevations:
Pueblo 4662
Colorado Springs 6008
Denver 5260
Telluride 8792
Aspen 7907
Vail 8380
Estes Park 7522
References:
1.Tissot Van Patot MC, Hill AE, Dingmann C, Gaul L, Fralick K, Christians U, et al. Risk of Impaired Coagulation in Warfarin Patients Ascending to Altitude (>2400 m). High Alt Med & Bio 2006;7(1):39-46.
2. www.colorado.com/static.php?file=elevation. Accessed May 3, 2006.
©2006 Sara K. Singh
See a related article www.warfarinfo.com/airtravel.htm
Editor's Note:
I'm somewhat confused by the emphasis placed on air travel, dehydration and high altitude studies because the first description of this in the medical literature was about people who were probably below sea level in the humid London Underground subway system sitting for hours in a cramped position because the Germans were bombing their city. Simply sitting still for hours seems to have been overlooked by current researchers.
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Last updated May 8, 2006