Activated Coagulation Time
Does this test have other names?
ACT, activated clotting time
What is this test?
This test measures how long it takes your blood to clot. It's often used to check
how well a medicine called heparin is working. Heparin slows the ability of blood
to clot, and the ACT test helps your healthcare provider find the right dosage. This
test uses whole blood, which is different from the standard tests for coagulation.
Those tests use plasma. Plasma is blood that has had the red cells, white cells, and
platelets removed. The ACT test is usually used during procedures when results may
be needed right away.
Why do I need this test?
You may need this test if you are getting heparin to prevent your blood from clotting
during a procedure such as open heart surgery, cardiac catheterization, or kidney
dialysis. This test is usually done in the hospital at your bedside.
What other tests might I have along with this test?
You may have other blood tests to measure how quickly your blood clots. A blood test
called activated partial thromboplastin time (APTT) is often done as a backup to the
results of the ACT test.
What do my test results mean?
Test results may vary depending on your age, gender, health history, and other things.
Your test results may be different depending on the lab used. They may not mean you
have a problem. Ask your healthcare provider what your test results mean for you.
This test doesn't measure the amount of heparin in your blood. It measures only how
long it takes for a blood clot to form. The results are given in the number of seconds:
The therapeutic range is usually about double the normal clotting time. It's important
to be in this range because if your ACT is too low, you may be in danger of a blood
clot forming during a procedure. Some procedures may require an even longer ACT.
If your ACT is too high, you may be in danger of bleeding.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection,
bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight
stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Many things may affect your lab test results. These include the method each lab uses
to do the test. Even if your test results are different from the normal value, you
may not have a problem. To learn what the results mean for you, talk with your healthcare
Other factors that may affect your results include:
The effects of surgery
Other medicines you are taking
Getting IV (intravenous) fluids, which can dilute your blood
Platelet counts and platelet function
Coagulation factor deficiencies
How do I get ready for this test?
You don't need to prepare for this test. But be sure your healthcare provider knows
about all medicines, herbs, vitamins, and supplements you are taking. This includes
medicines that don't need a prescription and any illegal drugs you may use.