LAB TEST
Prothrombin time (PT)
Prothrombin time (PT) is a blood test that measures the time it takes for the liquid portion (plasma) of your blood to clot. It measures the function of a part of the clotting system. A related blood test is partial thromboplastin time (PTT) , which measures the function of a different part of the clotting system.
How the Test is Performed
A blood sample is needed . If you are taking blood-thinning medicines, you will be watched for signs of bleeding.
How to Prepare for the Test
Certain medicines can change blood test results. Your health care provider will tell you if you need to stop taking any medicines before you have this test. This may include aspirin, heparin, antihistamines, and vitamin C. DO NOT stop or change your medicines without talking to your provider first. Also, tell your…
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Why the Test is Performed
The most common reason to perform this test is to monitor your levels when you are taking a blood-thinning medicine called warfarin (Coumadin). You are likely taking this medicine to prevent blood clots. Your provider will check your PT regularly to monitor and adjust the dose of warfarin. You may also need this test…
Normal Results
PT is measured in seconds. Most of the time, results are also given as what is called INR (international normalized ratio). If you are not taking blood thinning medicines, such as warfarin, the normal range for your results is: PT of 11 to 13.5 seconds INR of 0.8 to 1.1 If you are taking warfarin to prevent blood…
What Abnormal Results Mean
If you are not taking blood thinning medicines, such as warfarin, an INR result above 1.1 means your blood is clotting more slowly than normal. This may be due to: Bleeding disorders, a group of conditions in which there is a problem with the body's blood clotting process. Disorder in which the proteins that control…
Risks
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. Other risks associated with having blood drawn are slight, but may…
References
Lee GM, Ortel TL. Antithrombotic therapy. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods . 24th ed. Philadelphia, PA: Elsevier; 2022:chap 43. Schafer AI. Approach to the patient with bleeding and thrombosis. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine .…
This is a summary. Read the full article at www.ucsfbenioffchildrens.org (reviewed 02/02/2023).
This page is general information and is not medical advice. It does not replace a registered doctor, and it is not a prescription or a recommendation to use any medicine or test. Prices are listed prices and may change. Always follow the advice of your doctor or pharmacist.