Activated Clotting Time

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Update Date 12/05/2020
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Know the basics

What is Activated clotting time?

The activated clotting time (ACT) test is commonly ordered to measure the effect of some anticoagulants such as heparin or direct thrombin inhibitors; these medicines are used in angioplasty, kidney dialysis, and cardiopulmonary bypass (CPB)

The test measures the clotting time after adding some stimulants. By checking a clotting condition with ACT, your doctor can observe your condition when you receive a treatment with anticoagulants such as heparin.

Both APPT (activated partial thromboplastin time) and ACT (activated clotting time) can be ordered to observe the treatment with heparin for patients during CPB (cardiopulmonary bypass). However, ACT has more strong points than APTT.

First, ACT is more accurate than APTT when high-dose heparin is used to against coagulation. It is especially useful to clinical situations requiring high-dose heparin, including CPB, when high-dose coagulants are essential 10 times more than vein thrombosis. APTT cannot measure these high-dose conditions. The target of ACT is 400-480 seconds in CPB (cardiopulmonary bypass)

Second, ACT is less expensive and more easily done; it even can be done at the bed. It allows accessing instantly and reducing time to do through departments.

Why is Activated clotting time performed?

Because ACT is less expensive and more easily done; it even can be done at the bed. Therefore, it is really useful to patients who:

  • Percutaneous coronary intervention;
  • Kidney dialysis;
  • Cardiopulmonary bypass;

Things to know before

What should I know before receiving Activated clotting time?

These following factors affect the result:

  • Biological conditions such as hypothermia, blood dilution, the number and function of platelets.
  • Factors affecting pharmacokinetics of heparin (eg, kidney diseases or liver diseases) and anti-heparin can affect the ACT result.
  • A clot may increase the ACT result more than normal, which falsifies the result.

It is important you understand the warnings and precautions before having this surgery. If you have any questions, please consult with your doctor for more information and instructions.

Know what happens

How to prepare for Activated clotting time?

Before the test, you do not need to prepare anything particularly. However, your doctor may notice your health condition. You should ask him/her if you need any certain preparation.

When having an examination, you should wear a short-sleeved shirt. It’s easy for the nurse to collect blood from your hand.

What happens during Activated clotting time?

Healthy professionals collecting blood will:

  • Wrap a bandage around your hand to stop the blood from flowing.
  • Disinfect the injection site with alcohol.
  • Inject into the vein. More than 1 injection if it’s necessary.
  • Attach a hose for the blood to flow out.
  • Remove the bandage after taking enough blood.
  • Rub a gauze or silk-cotton on the injection site.
  • Stick a first-aid bandage on the injection.

What happens after Activated clotting time?

While you may not feel any pain after the injection, some people may feel a pain like a needle sting as the needle is inserting through your skin. However, when the needle stays in the vein and starts to suck blood, most of people no longer feel pain. Generally, your level of pain depends on the skill of the nurse, your vein’s condition and your sensitivity to pain.

After taking blood, you need wrapping with a bandage and slightly pressing on the vein to stop the bleeding. You can live normally after the test.

If you have any questions about the activated clotting time test, please consult with your doctor to better understand your instructions.

Understand the results

What do my results mean?

Depending on your laboratory you choose, the normal range for the activated clotting time test may vary.

Normally, the normal range of the test will be written down on the result paper. Discuss with our expert or doctor before the test and after receiving the result for an accurate result.

Normal result

Blood clots in 70-120 seconds.

If you have an anticoagulant therapy, the normal value is 150-600 seconds.

Abnormal result

It takes longer time for blood to clot maybe because:

  • Using Heparin;
  • Lack of clotting factors;
  • Cirrhosis;
  • Lupus inhibitors;
  • Using Warfarin.

It takes shorter time for blood to clot maybe because blood clots, which are abnormal blood clots in the vessel.

Depending on the laboratory and hospital, the normal range for the activated clotting time test may vary. Please discuss with your doctor any questions you may have about your test results.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Read also:


    Pagana, Kathleen D, and Timothy J. Pagana. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis, Mo: Mosby/Elsevier, 2010. Printed. 9 - 10.
    ACT: The Test | Activated Clotting Time. (n.d.). Accessed Jul 4 2016.
    Activated Clotting Time: Reference Range, Interpretation, Collection and Panels. (n.d.). Accessed Jul 4 2016.
    Activated clotting time (ACT). - PubMed - NCBI. (n.d.). Accessed Jul 4 2016.

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    Written by Nha Ngo
    Published on 09/10/2017