Partial thromboplastin time (PTT) is a blood test that looks at how long it takes for blood to clot. It can help tell if you have bleeding or clotting problems.
APTT; PTT; Activated partial thromboplastin time
The health care provider uses a needle to take blood from one of your veins. The blood collects into an air-tight container. You may be given a bandage to stop any bleeding. If you are taking a medicine called heparin, you will be watched for signs of bleeding.
The laboratory specialist will add chemicals to the blood sample and see how many seconds it takes for the blood to clot.
The health care provider may tell you to stop taking certain drugs before the test. Drugs that can affect the results of a PTT test include antihistamines, vitamin C (ascorbic acid), aspirin, and chlorpromazine (Thorazine).
Do not stop taking any medicine without first talking to your doctor.
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Your doctor may order this test if you have problems with bleeding or blood clotting. When you bleed, the body launches a series of activities that help the blood clot. This is called the coagulation cascade. There are three pathways to this event. The PTT test looks at special proteins, called factors, found in two of these pathways.
The test may also be used to monitor patients who are taking heparin, a blood thinner.
A PTT test is usually done with other tests, such as the prothrombin test.
The normal value will vary between laboratories. In general, clotting should occur between 25 to 35 seconds. If the person is taking blood thinners, clotting takes up to two and a half times longer.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
An abnormal (too long) PTT result may be due to:
This test is often done on people who may have bleeding problems. The risks of bleeding and hematoma in these patients are slightly greater than for people without bleeding problems.
In general, risks of any blood test may include:
Schafer AI. Approach to the patient with bleeding and thrombosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 178.
Review Date: 2/21/2009
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright ©2010 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.
Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Medical Center. Please discuss with your doctor any questions or concerns you may have.