Activated Coagulation Time (ACT)

Activated Coagulation Time (ACT) is a test used to measure how long it takes for your blood to clot. This test is frequently done to monitor high-dose heparin anticoagulation (how thin your blood is) when undergoing cardiopulmonary bypass and dialysis. A high dose of heparin prevents clot formation and can therefore cause bleeding. High doses of heparin are usually given to prevent clotting during surgical procedures such as cardiopulmonary bypass.

If the amount of heparin administered is not enough to inhibit the body's clotting system, blood clots may form in blood vessels throughout the body. If there is too much heparin the patient may experience excessive, even life threatening, bleeding. The ACT is sometimes used, along with the prothrombin time (PTT) to help determine whether a bleeding episode is due to excessive anticoagulation or to a depletion in clotting factors (proteins that are used up in the clotting process that can be replaced by giving the patient fresh frozen plasma).


No preparation is necessary. A blood sample is obtained by inserting a needle into a vein in the arm.


  • 70-180 seconds

  • Therapeutic range for anticoagulation: 150-210 seconds

(Normal ranges and anticoagulation ranges vary according to particular therapy.)

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.