• S Selleng, B Malowsky, U Strobel, A Wessel, T Ittermann, H-G Wollert, T E Warkentin, and A Greinacher.
• Institut für Immunologie und Transfusionsmedizin, Ernst-Moritz-Arndt Universität, Greifswald, Germany.
• J. Thromb. Haemost. 2010 Jan 1;8(1):30-6.

BackgroundThe high frequency of thrombocytopenia in post-cardiac surgery patients makes it challenging to diagnose heparin-induced thrombocytopenia (HIT). Two platelet count profiles are reported as indicating possible HIT in these patients: profile 1 describes a platelet count fall that begins between postoperative days 5 and 10, whereas profile 2 denotes early-onset thrombocytopenia that persists beyond day 5.ObjectivesTo examine how these platelet count profiles correlate with antibody status and HIT post-cardiac surgery.MethodsWe prospectively screened 581 cardiac surgery patients for heparin-dependent antibodies by platelet factor 4 (PF4)-heparin immunoassay and platelet-activation test, and performed daily platelet counts (until day 10) with 30-day follow-up.ResultsAll three patients with platelet count profile 1 tested positive for platelet-activating anti-PF4-heparin IgG antibodies [odds ratio (OR) 521.7, 95% confidence interval (CI) 3.9-34,000, P = 0.002], and were judged to have HIT. In contrast, none of 25 patients with early-onset and persisting thrombocytopenia (profile 2) was judged to have HIT, including five patients testing positive for platelet-activating anti-PF4-heparin IgG antibodies. In these patients, the frequency of heparin-dependent antibodies did not differ from that in non-thrombocytopenic controls, either for anti-PF4-heparin IgG (OR 1.7, 95% CI 0.7-4.1, P = 0.31) or for platelet-activating antibodies (OR 1.9, 95% CI 0.6-5.7, P = 0.20). Multivariate analysis revealed that type of cardiac surgery, but not HIT antibody status, predicted early-onset and persisting thrombocytopenia. Together, these findings show that HIT was uncommon in this study population [overall frequency, 3/581 (0.5%), 95% CI 0.1-1.5%].ConclusionsThrombocytopenia that begins between 5 and 10 days post-cardiac surgery is highly predictive for HIT. In contrast, early-onset and persisting thrombocytopenia is usually caused by non-HIT factors with coinciding heparin-dependent antibody seroconversion.

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