Travel Series: Altitude and Your INR

Publication Date: 
Sun, 07/01/2012
By: Alere Staff

People love to travel, sightsee and explore interesting places. Travel can often change your routine and habits.

Changes in diet, physical activity, stress can influence your INR (International Normalized Ratio). You can travel safely while taking warfarin; just keep the same routine you have at home.

Altitude change may affect your INR. Nearly 200,000 people taking warfarin visit a resort at altitude exceeding 7,500 feet annually in Colorado alone.1 Many more are traveling to other areas of elevation in the United States as well as in countries across the world. Healthcare providers have expressed concern that high altitude residents or visitors taking warfarin may a change in their INR as they ascend to or descend from elevation.1, 2

You may or may not have a change in your INR when flying. An review of three studies has showed that traveling to high altitude can frequently lead to INR instability.2 The review also revealed that traveling to high altitude resulted in a decrease in INR value.2 Talk to your doctor before traveling to a higher altitude or descending from a higher altitude so that your INR can be monitored more closely.

Increasing testing frequency is recommended when making any changes to your diet, medication, etc. Studies have shown that increasing testing frequency with weekly testing of INR improves patient safety and helps keep the drug in its therapeutic effective zone.3,4 Weekly testing was shown to be the most effective testing frequency.3 Medicare and many private/commercial insurance reimburse patients for weekly patient self-testing.5 Go to the Getting Started page or call Alere at 1.800.504.4032 for more information about testing your INR at home.

  1. Van Patot MC, Hill AE, Dingmann C, Gaul L, Fralick K, Christians U, Honigman B, Salman MD. Risk of impaired coagulation in warfarin patients ascending to altitude (>2400 m). High Alt Med Biol. 2006 Spring;7(1):39-46.
  2. Mortenson, Duane, “Changes in Coagulation Factors at High Altitude: A Systematic Review” (2011). School of Physician Assistant Studies. Paper 248.
  3. Am J Manag Care. 2014;20(3):202-209.
  4. Heneghan C., et al. Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. 2006. Lancet, 367, 404-11.
  5. Center for Medicare and Medicaid Services. Decision Memo for Prothrombin Time (INR) Monitor for Home Anticoagulation Management  (CAG-00087R) [Memorandum]. 2008. Baltimore, MD.