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). (Level of Evidence B)  Serum tests that include functional testing with se- rotonin release assay (SRA) or heparin-induced platelet activation (HIPA) can be bene cial in iden- tifying patients with HIT who have a history of thrombocytopenia, and elevated clinical HIT risk scores, when platelet factor 4 (PF4) heparin antibody testing is inconclusive (weakly positive) for HIT. (Level of Evidence C)  For patients who are seropositive for heparin- platelet antibodies or have a recent history of HIT, it is reasonable to delay elective cardiac operations requiring CPB until a patient s functional test or antigenic (antibody) assay are negative, with the expectation that heparin anticoagulation therapy for CPB is likely to be safe and effective. (Level of Evi- dence C)  For patients with a diagnosis of HIT and in need of an urgent operation requiring CPB, anticoagulation with bivalirudin is a reasonable option. (Level of Evidence B) Class IIb Recommendation  In patients with signi cant renal dysfunction who are seropositive for HIT and require urgent opera- tion requiring CPB, use of plasmapheresis, arga- troban, or heparin with antiplatelet agents (such as tiro ban, ilioprost) may be considered, understand- ing that there are increased risks of bleeding with these interventions. (Level of Evidence C) The chief contraindications to the use of heparin for CPB are a history of HIT and known hypersensitivity to heparin. 