From an inquirer to the American Society for Clinical Laboratory Science Consumer Forum (with permission):
I have a titanium aortic valve. I sometimes experience atrial fibrillation (afib). My cardiologist wants my prothrombin time/international normalized ratio (PT/INR) to be 2.5–3.5. I take 5 mg daily of warfarin. One day per week I take 7.5 mg. I also take a baby aspirin (81 mg) daily as per the cardiologist. Today my PT was 2.8 (perfect for me and it is usually pretty steady). I am aware of most of the foods high in vitamin K and try to use them sparingly and consistently. My question relates to changes in altitude, as in a trip to Colorado, and the possible effects on PT/INR in staying at high altitude for a week. Will this raise or lower my PT/INR? I live at sea level. I will be up around 8-10,000 feet for a week! What will happen to the value upon return home? I also consume alcohol in the form of beer and wine. I sometimes consume more when on vacation. The last time we went to Colorado, we were there for one week and did consume beer at the various breweries. When I came home, I was working in the yard and developed a hematoma on my wrist. When I sought treatment, my PT/INR was 5.8! Do you think the PT/INR elevationwas attributable to alcohol consumption, going up in altitude for a week, or coming down, or a combination of all of the above? Any advice for my next trip?
Here is my answer to the inquirer: Hello and thank you for your question. Short-term high altitude (several hours’ exposure) has no effect upon the PT/INR, as shown in several studies conducted using hypobaric chambers. These studies were mostly concerned with the possibility of thrombosis subsequent to prolonged air travel, the condition commonly called “economy-class syndrome,” or the condition that affects mountain climbers, high-altitude neurological or pulmonary edema (HANE, HAPE). There are no studies that employ several days’ exposure, though it is probably safe to generalize from the short-term hypobaric chamber studies.
Alcohol is a more likely culprit. I don’t conclude from your message that you are either a chronic or binge drinker. Chronic long-term alcohol consumption at a level that can damage the liver is a known cause of bleeding, as liver damage reduces the production of the coagulation factors. This can be verified by repeating the PT/INR and simultaneously testing for the liver enzymes. However, liver damage at this level is only seen in chronic long-term, high-volume drinking as is typical in alcoholic cirrhosis, which doesn’t match your description.
Binge drinking, by comparison, tends to suppress platelet function, which also leads to bleeding such as the hematoma you experienced, however platelet suppression is not reflected in the PT/INR. Consequently, there is really no firm answer to your question.
I promised the inquirer I would post this for our Fritsma Factor participants to learn if anyone else has seen PT/INR changes related to altitude or alcohol. Please respond here if you have seen this. Geo.
Thank you, Gary. This is interesting and raises the question
Thank you, Gary. This is interesting and raises the question of altitude and the INR again. Given the consistency over time, it would be worth studying further.
I have done so. Since I was originally operated on at over 6
I have done so. Since I was originally operated on at over 6000 ft and dosed with acenocumarol for several weeks before returning to sea level, I was forced to lower the dose while at the beach. Both labs, the most reputable in either area, assure me that they use the same reagent, but that the control groups could be different, thus causing the difference. In any case, over the past 6+ years I have been able to keep my INR between 2 and 4.5, as ordered by the cardiologist, by adding 1 mg to the dosis when I am at the higher altitude. I offer this info only as a report of my experience, not as a recommendation.
This again raises the possibility that the INR is affected b
This again raises the possibility that the INR is affected by altitude, however it is more likely that interlaboratory variation is the culprit, despite the claim that the INR should be the same everywhere. Rather than adjusting your dosage, you may wish to try different laboratories in either location.
I normally live on the Pacific coast of Mexico, and take 2 m
I normally live on the Pacific coast of Mexico, and take 2 mg of acenocumarol (a warfarin) nightly. This keeps my INR between 2.5 and 4. (I have a titanium aortal valve.) When I visit my other home, in San Miguel de Allende, at 6200 ft., my INR decreases to 1.7 to 2.3. I therefore increase my nightly dose to 3 mgs, which puts my INR back in the correct range. If, however I continue the 3 mg dose while at the beach, my INR goes to over 5, so I reduce the dose again to 2 mg.