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PT and INR
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Common Questions
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1. Can I do this test at home?
2. Should I have it done at the same time of day?
3. My PT results vary sometimes, yet my doctor doesn’t change my prescription. Why?
1. Can I do this test at home?
Yes. The Food and Drug Administration has approved several home PT/INR testing machines. However, home testing is usually done in the context of a home-based coagulation management program that involves patient training and defined response and management protocols.
2. Should I have it done at the same time of day?
It is not generally necessary to have your PT/INR measured at a particular time of day. It is, however, important that you take your anti-coagulation medication at the same time each day to maintain a continuous level. If your doctor increases or decreases your dosage, they may want you to have your blood rechecked in a day or so to judge the effect of the dosage change on your PT/INR (it is not an immediate effect).
3. My PT results vary sometimes, yet my doctor doesn’t change my prescription. Why?
The use of any of the drugs mentioned above can alter your results, as can the use of diuretics and antihistamines and the onset of illness or allergies. Certain foods, such as beef and pork liver, green tea, broccoli, chickpeas, kale, turnip greens, and soybean products contain large amounts of vitamin K and can alter PT results. The blood collection technique and the difficulty in obtaining the blood sample can also affect test results. If your doctor has concerns about the stability of your PT/INR, he may test your blood more frequently.
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This article was last reviewed on
May 6, 2005.
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