Type your tag names separated by a space and hit enter

Activated clotting time


Activated clotting time, whole blood (ACT)

70–180 sec (method-specific)


Obtain blood in a plastic syringe without anticoagulant. Test should be performed immediately at patient’s bedside. A clean venipuncture is required.

A special vacutainer tube containing activator (eg, celite, kaolin) is also available.

Physiologic Basis

ACT is a point-of-care test used to monitor high-dose heparin as an anticoagulant during cardiac surgery (extracorporeal circulation), angioplasty, and hemodialysis. It is also used to determine the dose of protamine sulfate to reverse the heparin effect on completion of the procedure.

ACT is also used to monitor heparin or direct thrombin inhibitor in patients with lupus anticoagulant.


Prolonged in: Heparin therapy, direct thrombin inhibitor therapy, severe deficiency of clotting factors (except factors VII and XIII), functional platelet disorders.

In general, the accepted goal during cardiopulmonary bypass surgery is 400–500 sec. For carotid artery stenting, the optimal ACT is 250–300 sec.


ACT is the choice of test when heparin levels are too high (eg, > 1.0 U/mL heparin) to allow monitoring with PTT and/or when a rapid result is necessary to monitor treatment.

Because different methodologies and a number of variables (eg, platelet count and function, hypothermia, hemodilution, and certain drugs like aprotinin) may affect the ACT, the ACT test is not yet standardized. Reproducibility of prolonged ACTs may be poor.

Finley A et al. Review article: heparin sensitivity and resistance: management during cardiopulmonary bypass. Anesth Analg 2013;116:1210.  [PMID: 23408671]

McNair E et al. Bivalirudin as an adjunctive anticoagulant to heparin in the treatment of heparin resistance during cardiopulmonary bypass-assisted cardiac surgery. Perfusion 2016;31:189.  [PMID: 25934498]

Sniecinski RM et al. Anticoagulation management associated with extracorporeal circulation. Best Pract Res Clin Anaesthesiol 2015;29:189.  [PMID: 26060030]

Activated clotting time is a sample topic from the Guide to Diagnostic Tests.

To view other topics, please or purchase a subscription.

Emergency Central is a collection of disease, drug, and test information including 5-Minute Emergency Medicine Consult, Davis’s Drug, McGraw-Hill Medical’s Diagnosaurus®, Pocket Guide to Diagnostic Tests, and MEDLINE Journals created for emergency medicine professionals. Learn more.


McPhee, Stephen J., et al. "Activated Clotting Time." Guide to Diagnostic Tests, 7th ed., McGraw-Hill Education, 2017. Emergency Central, emergency.unboundmedicine.com/emergency/view/GDT/619152/all/Activated_clotting_time.
McPhee SJ, Lu CM, Nicoll D. Activated clotting time. Guide to Diagnostic Tests. 7th ed. McGraw-Hill Education; 2017. https://emergency.unboundmedicine.com/emergency/view/GDT/619152/all/Activated_clotting_time. Accessed April 20, 2019.
McPhee, S. J., Lu, C. M., & Nicoll, D. (2017). Activated clotting time. In Guide to Diagnostic Tests. Available from https://emergency.unboundmedicine.com/emergency/view/GDT/619152/all/Activated_clotting_time
McPhee SJ, Lu CM, Nicoll D. Activated Clotting Time [Internet]. In: Guide to Diagnostic Tests. McGraw-Hill Education; 2017. [cited 2019 April 20]. Available from: https://emergency.unboundmedicine.com/emergency/view/GDT/619152/all/Activated_clotting_time.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Activated clotting time ID - 619152 A1 - McPhee,Stephen J, AU - Lu,Chuanyi Mark, AU - Nicoll,Diana, BT - Guide to Diagnostic Tests UR - https://emergency.unboundmedicine.com/emergency/view/GDT/619152/all/Activated_clotting_time PB - McGraw-Hill Education ET - 7 DB - Emergency Central DP - Unbound Medicine ER -