Partial Thromboplastin Time
time (PTT) is a blood test that measures the time it takes your blood to clot.
A PTT test can be used to check for bleeding problems.
clotting factors are needed for blood to clot
(coagulation). The partial thromboplastin time is an important test because the
time it takes your blood to clot may be affected by:
- Blood-thinning medicine, such as heparin.
Another test, the activated partial thromboplastin time (APTT) test, may be used to find out if the right dose of heparin is being
- Low levels of blood clotting factors.
- A change in
the activity of any of the clotting factors.
- The absence of any of
the clotting factors.
- Other substances, called inhibitors, that
affect the clotting factors.
- An increase in the use of the clotting
Another blood clotting test, called prothrombin time (PT) or INR
(international normalized ratio),
measures other clotting factors. Partial thromboplastin time and prothrombin
time are often done at the same time to check for bleeding problems caused by a
problem with the clotting factors.
Why It Is Done
Partial thromboplastin time (PTT) is
- Find a cause of abnormal bleeding or
- Check for low levels of blood clotting factors. The lack
of some clotting factors can cause bleeding disorders such as
- 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
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
The health professional drawing blood
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure to the site and then a