Activated Clotting Time Test (ACT) – Why am I having this test?
Activated clotting time test is used to measure how long it takes for your blood to clot. This test is done to monitor the blood-thinning (anticoagulant) effect of heparin or certain other blood-thinning medicines during some procedures.
If too little heparin is given, blood clots may form in blood vessels throughout your body. If too much heparin is given, you may experience excessive bleeding. This could be life-threatening.
An ACT test is sometimes used along with an activated partial thromboplastin time (aPTT) test to monitor heparin therapy during some procedures. These include procedures to:
- Take over the work of the heart during surgery (cardiopulmonary bypass, or CPB).
- Open clogged arteries using a balloon (cardiac angioplasty).
- Purify blood when the kidneys have stopped working (hemodialysis).
What is being tested?
An ACT test measures the time it takes for whole 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 are the results reported?
Your test results will be reported as a range in time (in seconds). Your health care provider will compare your results to normal ranges that were established after testing a large group of healthy people (reference ranges). Reference ranges may vary among labs and hospitals. For this test, results may be in one of these ranges:
- Therapeutic range for anticoagulation: 150–600 seconds. This refers to the target time by which a person’s blood should clot if he or she is taking heparin or other blood-thinning medicines.
- Normal range: 70–120 seconds. This is the normal time that blood takes to clot without any heparin or other blood-thinning medicines.
What do the results mean?
- Increased
ACT can be seen if you:
- Are receiving heparin or the blood thinner called warfarin.
- Have certain clotting factor deficiencies.
- Have cirrhosis of the liver.
- Have certain antibodies that act against components involved in the clotting process (lupus inhibitors).
- Decreased ACT can be seen if you have blood clots (thrombosis).
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
- An activated clotting time (ACT) test is used to measure how long it takes for your blood to clot.
- This test is done to monitor the blood-thinning (anticoagulant) effect of heparin or certain other blood-thinning medicines during some procedures.
- This test may be used during procedures that are done to open clogged arteries (cardiac angioplasty), purify the blood (hemodialysis), or take over the work of the heart during surgery (cardiopulmonary bypass).
