Partial Thromboplastin Time (PTT) Test

Why It Is Done

Partial thromboplastin time (PTT) is done to:

• Find a cause of abnormal bleeding or bruising.
• Check for low levels of blood clotting factors. The lack of some clotting factors can cause bleeding disorders such as hemophilia.
• Check for conditions that cause clotting problems. Conditions such as antiphospholipid antibody syndrome or lupus anticoagulant syndrome develop when the immune system makes antibodies that attack blood clotting factors. This can cause the blood to clot easily in veins and arteries.
• Check if it is safe to do a procedure or surgery that might cause bleeding.
• Check how well the liver is working.

The activated partial thromboplastin time (APTT) test is used after you take blood-thinners to see if the right dose of medicine is being used. If the test is done for this purpose, an APTT may be done every few hours. When the correct dose of medicine is found, you will not need so many tests.

How To Prepare

Many medicines can change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

Abnormal values

• A longer-than-normal PTT or APTT can mean a lack of or low level of one of the blood clotting factors or another substance needed to clot blood. This can be caused by bleeding disorders, such as hemophilia or von Willebrand's disease.
• A longer-than-normal PTT or APTT can be caused by liver disease, kidney disease (such as nephrotic syndrome), or treatment with blood thinners.
• A longer-than-normal PTT may be caused by conditions such as antiphospholipid antibody syndrome or lupus anticoagulant syndrome. These conditions happen when the immune system makes antibodies that attack blood clotting factors. This can cause the blood to clot easily in veins and arteries.
• The PTT can get longer when you are using heparin, so your PTT value needs to be closely checked. If you have a longer PTT, you may have a higher risk of bleeding.