True hypersensitivity to heparin is rare, yet can occur in patients allergic to heparin or the sources of heparin (eg, porcine or bovine sources of heparin) [35, 36, 62 64]. Pa- tients clinically suspected of having hypersensitivity to heparin should undergo testing to con rm the diagnosis as soon as possible, given the often urgent need for heparin anticoagulation in a variety of clinical settings [35]. The decision to utilize an alternative anticoagulant agent during CPB is based on the urgency of the cardiac procedure and on heparin antibodies capable of acti- vating platelets. The American College of Chest Physi- cians recommends delaying nonurgent cardiac procedures until heparin antibodies are no longer detectable [43]. The single most cumbersome aspect of heparin alternatives is inability to rapidly reverse anti- coagulation after weaning from CPB. For nearly all hep- arin alternatives, there is no reversal agent equivalent to protamine. Other negative side effects include prolonged operative times and the risk of increased blood loss and transfusion. Although several agents have been used as alternates to heparin [45, 52], there is only suf cient data on bivalirudin to make recommendations in this clinical setting. Bivalirudin Bivalirudin, a recombinant direct thrombin inhibitor, is not currently approved by the Food and Drug Adminis- tration for use during CPB (albeit approved for this use outside the United States). Bivalirudin effectively inhibits the coagulation cascade and has a short 25-minute half- life in patients with normal renal function. Monitoring of anticoagulation with bivalirudin is more challenging than with heparin. The ecarin clotting time (ECT) corre- lates strongly (R2 0.91) with therapeutic bivalirudin concentrations but is not commonly available as a point- of-care test [65]. In a comparative analysis study of 10 patients undergoing cardiopulmonary bypass, three different methods of the ACT test were compared with ECT [66]. 