Urgent Cardiac Surgery in a Patient with a Remote History of Heparin-Induced Thrombocytopenia: Use of the Anti-PF4/Heparin ELISA Confirmatory Test

In Brief The use of established heparin protocols when heparin-induced thrombocytopenia (HIT) antibodies are negative is currently recommended for the management of patients with previous HIT who require cardiac surgery. Routine preoperative testing for HIT antibodies using an anti-PF4/heparin enzyme-linked immunosorbent assay (ELISA) introduces the problem of detecting nonpathogenic HIT antibodies, which can lead to a false diagnosis of the presence of platelet-activating antibodies. Our case report demonstrates the clinical utility of a newer confirmatory procedure performed using high dose heparin. We use this procedure in situations in which pretest probability is low (remote HIT) and the anti-PF4/heparin ELISA test results are weak to moderately positive (absorbance 0.4-1.0). IMPLICATIONS: The use of a clinicopathologic approach to the diagnosis of heparin-induced thrombocytopenia (HIT) requires caution when the antigen-based test for HIT antibodies is performed in patients with a low pretest probability of HIT. We describe here a valuable adjunct to the clinical history when recommending heparin use in patients with a positive enzyme-linked immunosorbent assay (ELISA) screening test result: an anti-PF4/heparin ELISA with a confirmatory procedure.