Prothrombin Time: Results
Content provided by Healthwise
Results
Prothrombin time (PT) is a blood test that measures how long it takes blood to clot.
Normal
Normal values may vary from lab to lab.
A method of standardizing prothrombin time results, called the international normalized ratio (INR) system, has been developed so the results among labs using different test methods can be understood in the same way. Using the INR system, treatment with blood-thinning medicine (anticoagulant therapy) will be the same. In some labs, only the INR is reported and the PT is not reported.
Normal: | 10–13 seconds |
|---|---|
International normalized ratio (INR): | 1.0–1.4 |
The warfarin (Coumadin) dose is changed so that the prothrombin time is longer than normal (by about 1.5 to 2.5 times the normal value or INR values 2 to 3). Prothrombin times are also kept at longer times for people with artificial heart valves, because these valves have a high chance of causing clots to form.
Abnormal values
- A longer-than-normal PT can mean a lack of or low level of one or more blood clotting factors (factors I, II, V, VII, or X). It can also mean a lack of vitamin K; liver disease, such as cirrhosis; or that a liver injury has occurred. A longer-than-normal PT can also mean that you have disseminated intravascular coagulation (DIC), a life-threatening condition in which your body uses up its clotting factors so quickly that the blood cannot clot and bleeding does not stop.
- A longer-than-normal PT can be caused by treatment with blood-thinning medicines, such as warfarin (Coumadin) or, in rare cases, heparin.
| Last updated: | September 15, 2008 |
|---|---|
| Author: | Robin Parks, MS |
| Reviewed By: | Anne C. Poinier, MD - Internal Medicine, Brian Leber, MDCM, FRCPC - Hematology |
| Editors: | Maria Essig, Tracy Landauer |
© 1995-2007, Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
This information is not intended to replace the advice of a doctor. By using AOL Body, you indicate that you have read, understood, and agreed to our Terms of Service, and AOL Body Advertising Policy. Read more about our content partners.
Search
Where Does it Hurt?
If you're experiencing aches and pains we can help you find answers. Find out what your symptoms mean for your health.
