Heparin-Induced Thrombocytopenia With a False Negative Anti-PF4 Assay

<b>Background:</b> Heparin-induced thrombocytopenia (HIT) is an acquired prothrombotic state from anti-heparin platelet-factor 4 (PF4) mediated activation of platelets. Anti-PF4 assay is used to screen for HIT due to high sensitivity and negative predictive value. <b>Case Report:</b> We present a 74-year-old male that had clinical HIT with false negative anti-PF4 and subsequently positive serotonin release assay (SRA). Delay in cessation of heparin led to recurrent limb thrombosis in the setting of multiple revascularization attempts with a poor outcome. <b>Conclusion:</b> We re-emphasize the importance of clinical presentation in management of patients with suspected HIT.