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]