What is the ACT target during CPB and what does ACT measure?

• A. ACT > 200–300 seconds; measures time to clot formation under an activator
• B. ACT > 480–520 seconds; measures time to clot formation under an activator
• C. ACT > 800 seconds; measures fibrinogen level
• D. ACT > 100 seconds; measures hemoglobin

Answer: (B)

Activated Clotting Time (ACT) is a whole-blood test used during cardiopulmonary bypass to gauge the level of anticoagulation. It measures the time it takes for a clot to form after the blood is activated (with agents like kaolin or celite). Because heparin slows clot formation, the ACT lengthens as anticoagulation increases. On CPB, a typical target is about 480–520 seconds, which provides enough anticoagulation to keep the circuit patent while balancing bleeding risk. This test specifically reflects clot formation time under activation, not fibrinogen levels or hemoglobin. Shorter times (e.g., around 100–300 seconds) would indicate under-anticoagulation, while an excessively long time (e.g., 800 seconds) is not a standard CPB goal.