Early-onset and persisting thrombocytopenia in post-cardiac surgery patients is rarely due to heparin-induced thrombocytopenia, even when antibody tests are positive

See also Gruel Y, Pouplard C. Post‐operative platelet count profile: the most reliable tool for identifying patients with true heparin‐induced thrombocypenia after cardiac surgery. This issue, pp 27–29. Summary. Background: The 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. Objectives: To examine how these platelet count profiles correlate with antibody status and HIT post‐cardiac surgery. Methods: We 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. Results: All 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%]. Conclusions: Thrombocytopenia 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.