Activated Clotting Time

Activated clotting time (ACT) is test that is used to monitor the effectiveness of high dose heparin therapy. The ACT can be done at the bedside for patients experiencing: pulmonary embolus, extracorporeal membrane oxygenation (ECMO) and hemodialysis. The ACT is most often used in the Operating Room during cardiopulmonary bypass (CPB) surgery. High dose heparin anticoagulation during CPB and ECMO is necessary to reduce the risk of micro-thrombi due to the extracorporeal manipulation of blood.

Reference value for the ACT ranges between 70-180 seconds; the desirable range for anticoagulation depends upon the reason for heparinization. During CPB the desired range may exceed 400-500 seconds.

The ACT lacks correlation with other coagulation tests. In general it is used to demonstrate the inability to coagulate rather than quantifying the ability to clot. Results can be affected by: methodology, platelet count and function, hypothermia, hemodilution and certain drugs like aprotinin are among the important factors. Adherence to manufacturer guidelines and institutional practices is crucial. Manufacturers provide various methodologies, activators and reagents to make the test as precise as possible.

To collect a sample, draw undiluted blood from sites which have not been contaminated by heparin infusion. The whole blood must be immediately transferred to appropriate test vial, mixed with the activator and the timer activated on the ACT test equipment. Samples cannot be stored.

Click here for an article on Activated Clotting Time (ACT) Emergency Nursing World: Research Applied to Clinical Practice by Robert C. Knies, RN, MSN, CEN)

Look Look for the answer to this question: What natural anticoagulant (part of the intrinsic pathway) combines with heparin for instantaneous binding of coagulation factors, and immediate anticoagulation?

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