The tests that utilize a maximally activated sample also report less variability in clotting times and are less susceptible to prolongation by hypothermia and artifacts [10]. The maximal activation removes the variability induced by hemodilution of clot- ting factors. Maximal activation is also accomplished in the microcuvette ACT technology owing to the small sample volume and minimization of sample dilution. A plasma supplemented ACT accomplishes a similar result. This test has been shown to mitigate the ACT variability to more closely mirror anti-Xa levels; however, it is cumbersome and dif cult to perform at the point of care [19]. The viscoelastic tests have been modi ed for point-of- care measurement of the ACT and in a small ex vivo analysis in CPB patients, the two tests performed simi- larly to standard ACT tests with respect to heparinization and hemodilution [30, 31]. Another observational study involving 50 CPB patients demonstrated that a visco- elastic measurement of ACT activity mirrored the activity of both standard ACT tests and anti-Xa levels [32]. It remains uncertain what the threshold minimum safe values are for the viscoelastic clotting times in CPB and how they correspond with the historical 480 second target. Further clinical and outcome studies are war- ranted before switching patient management to a visco- elastic ACT test. 654 Ann Thorac Surg ANTICOAGULATION DURING CARDIOPULMONARY BYPASS 2018;105:650 62 REPORT Heparin Contraindications and Heparin Alternatives Class IIa Recommendations  Clinical scoring estimates that use a fall in platelet count greater than 50% or a thrombotic event be- tween 5 and 14 days after a heparin exposure can be used to determine whether a heparin platelet anti- body test should be performed to diagnose heparin- induced thrombocytopenia (HIT). 