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Partial Thromboplastin Time Test (PTT) -Why am I having this test?
Partial thromboplastin time test is done to monitor how your blood clots. When you get a tissue injury, blood cells gather at the site of the injury and clump together (clot) to stop the bleeding.
Blood clots can also form in the blood vessels and cause serious problems, such as stopping blood flow to parts of the body or causing a stroke or heart attack.
If you are taking a blood thinner (anticoagulant) to prevent or treat blood clots (such as heparin), you may have this test done at regular intervals to monitor your treatment. You may also have this test to:
- Evaluate liver function.
- Check for serious blood infections.
- Help diagnose clotting disorders.
What is being tested?
The PTT test measures how long it takes your blood to clot.
What kind of sample is taken?
A blood sample is required for this test. It is usually collected by inserting a needle into a blood vessel.
How do I prepare for this test?
Follow instructions from your health care provider about changing or stopping your regular medicines. This is especially important if you are taking diabetes medicines or anticoagulants.
Tell a health care provider about:
- All medicines you are taking, including vitamins, herbs, eye drops, creams, and over-the-counter medicines.
- Any blood disorders you have.
- Any medical conditions you have.
- Whether you are pregnant or may be pregnant.
How are the results reported?
Your test results will be reported as a value that indicates how long it takes, in seconds, for your blood to clot. Your health care provider will compare your results to normal ranges that were established after testing a large group of people (reference ranges). Reference ranges may vary among labs and hospitals. If you are not taking anticoagulant therapy, a common reference range for this test is:
- PTT: 60–70 seconds.
If you are taking anticoagulant therapy, your health care provider will compare your results to a reference value that may be called the “control value.” Your results will indicate how many times higher your clotting time is than the control value. A common reference range is:
- 1.5–2.5 times the control value, in seconds.
What do the results mean?
Results that are within your reference range are considered normal, meaning that your blood clots at an expected rate. This may mean that your anticoagulant therapy is working effectively, if applicable.
Results that are greater than your reference range mean that your blood clots too slowly. This may mean that:
- You have long-term scarring in your liver (cirrhosis).
- You lack certain substances that are needed to help the blood clot (clotting factor deficiency).
- You are taking medicine that slows down your clotting time.
- If you are taking anticoagulant therapy, you may need to work with your health care provider to decrease your dosage.
- You have a vitamin K deficiency.
Results that are lower than your reference range mean that your blood clots too quickly. This may be caused by certain types of cancer. More tests will be needed to make a diagnosis.
Talk with your health care provider about what your results mean.
Questions to ask your health care provider
Ask your health care provider, or the department that is doing the test:
- When will my results be ready?
- How will I get my results?
- What are my treatment options?
- What other tests do I need?
- What are my next steps?
Summary
- The partial thromboplastin time (PTT) test is done to determine how long it takes your blood to clot.
- If you are taking a blood thinner (anticoagulant), you may have this test done at regular intervals to monitor your treatment.
- Results that are within your reference range are considered normal, meaning that your blood clots at an expected rate.
- Results that are greater than your reference range mean that your blood clots too slowly. This may be caused by a disease or a medicine you are taking.
- Talk with your health care provider about what your results mean.