close window
Housecall Archives
About our e-newsletters
- Free e-newsletters
- Mayo Clinic expertise
- We do not share your e-mail address
Housecall, our weekly general-interest e-newsletter, keeps you up to date on a wide variety of health topics with timely, reliable, practical information, recipes, blogs, questions and answers with Mayo Clinic experts and more. Our biweekly topic-specific e-newsletters also include blogs, questions and answers with Mayo Clinic experts, and other useful information that will help you manage your health.
Housecall Archives
close window
Mayo Clinic Housecall
Stay up to date on the latest health information.
What you get
- Free weekly e-newsletter
- Mayo Clinic expertise
- Recipes, tools and other helpful information
- We do not share your e-mail address
Results
By Mayo Clinic staffProthrombin time test results can be presented in two ways:
- Prothrombin time in seconds. Prothrombin time is usually measured in seconds — the time it takes for your blood to clot. This way of determining prothrombin time creates results that will vary depending on the laboratory and the method used to test the blood, but a sample range is approximately 10 to 12 seconds. A number higher than average means it takes blood longer than usual to clot. A lower number means blood clots more quickly than expected.
- Prothrombin time as a value that represents a ratio. For people taking the blood-thinning medication warfarin (Coumadin), results are given as a number that represents a ratio called the international normalized ratio (INR). The INR is a calculation (ratio) of a measured prothrombin time test result to a normal value for a prothrombin time test taken in a specific laboratory. An INR range of 2.0 to 3.0 is considered standard for people taking warfarin, but may need to be higher for certain people. If your INR is higher than expected, that means your blood clots more slowly than desired. A lower INR means your blood clots more quickly than desired.
What your results mean
If your prothrombin time test reveals that your blood is clotting too slowly, this can be caused by:
- Blood-thinning medications, such as warfarin (Coumadin), heparin and aspirin
- Liver problems
- Inadequate levels of proteins (factors) that cause blood to clot
- Vitamin K deficiency
- Estrogen-containing medications, such as birth control pills and hormone replacement therapy
- Antacids to control heartburn
- Quinidine, a medication for heart rhythm problems
- Antibiotics to treat infections
- Allopurinol (Zyloprim), a medication used to treat gout
If your prothrombin time test reveals that your blood is clotting too fast, this can be caused by:
- Supplements that contain vitamin K
- High intake of foods that contain vitamin K, such as liver, broccoli, chickpeas, green tea, kale, turnip greens and products that contain soybeans
- Estrogen-containing medications, such as birth control pills and hormone replacement therapy
- Swelling in a vein caused by a blood clot (thrombophlebitis)
- Griseofulvin (Grifulvin V, Gris-Peg), an antifungal medication
- Diphenhydramine (Benadryl, others), an antihistamine
References
- Prothrombin time (PT). In: Ferri FF. Ferri's Clinical Advisor 2011. Philadelphia, Pa.: Mosby; 2010. http://www.mdconsult.com/book/player/book.do?method=display&type=aboutPage&decorator=header&eid=4-u1.0-B978-0-323-05610-6..C2009-0-38600-6--TOP&isbn=978-0-323-05610-6&uniq=210978719. Accessed July 22, 2010.
- Pratt DS. Liver chemistry and function tests. In: Feldman M, et al. Sleisinger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa.: Saunders; 2010. http://www.mdconsult.com/book/player/linkTo?type=bookHome&isbn=978-1-4160-6189-2&eid=4-u1.0-B978-1-4160-6189-2..X0001-7--TOP&uniq=200844987-3. Accessed July 22, 2010.
- PT and INR. Lab Tests Online. http://www.labtestsonline.org/understanding/analytes/pt/glance.html#. Accessed July 22, 2010.
- Laboratory reference values. Prothrombin time. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2010.
Find Mayo Clinic on