Figure 50-32 Graph illustrating the difference between heparin dose-response curves using the partial thromboplastin time (PTT, solid line), the whole blood coagulation time (WBCT), and the activated coagulation time (ACT, dashed line). The disadvantage of the PTT for measuring heparin effect is the exponential dose-response relationship. The advantage of ACT is that a straight line dose-response relationship exists that is similar to the WBCT, but the time is measured in seconds rather than minutes. Heparin half-life can be measured from both the WBCT and ACT, but not from the PTT. (From Young JA: Coagulation abnormalities with cardiopulmonary bypass. In Utley JR [ed]: Pathophysiology and Techniques of Cardiopulmonary Bypass. Baltimore, Williams & Wilkins, 1983.)