SHM Converge Scientific Abstract ePoster Gallery-When Hit Is Not a Hit: Unmasking Non-Pathogenic Pf4 Antibodies

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This case highlights the challenge of interpreting anti-PF4 testing in postoperative patients exposed to heparin. A 67-year-old man underwent surgical aortic valve replacement with cardiopulmonary bypass and heparin exposure. Two weeks later, he presented with chest/back pain, gum bleeding, petechiae, severe thrombocytopenia, and bilateral pulmonary emboli. Because of concern for heparin-induced thrombocytopenia (HIT), heparin was stopped and bivalirudin was started. His anti-PF4 antibody test was positive with a low optical density (0.734), but his platelet count did not improve after stopping heparin and switching anticoagulation. Hematology later considered immune thrombocytopenic purpura and gave dexamethasone. The confirmatory serotonin release assay (SRA) was negative, arguing against true HIT. He was discharged on apixaban for provoked pulmonary embolism.<br /><br />The discussion emphasizes that anti-PF4 is highly sensitive but not specific for HIT, especially after cardiopulmonary bypass, when many patients develop non-pathogenic anti-PF4 antibodies as part of an inflammatory postoperative response. Diagnosis should not rely on the PF4 test alone; it must be interpreted alongside clinical probability, such as the 4T score, and confirmed with a functional assay like the SRA. Higher optical density values are more strongly associated with true HIT, while low-positive results may reflect non-pathogenic antibodies.<br /><br />Key takeaway: early expert consultation is important to avoid misdiagnosis, unnecessary anticoagulant changes, and delayed recognition of the true cause of thrombocytopenia and thrombosis.

Asset Subtitle

Cassandra L. Pasadyn

Meta Tag

Author List Ali Shah, Cassandra L. Pasadyn, Deep Patel

Category Clinical Vignettes

Concept Heparin-Induced Thrombocytopenia

Concept 4T Score

Concept Anti-PF4/Heparin Immunologic Testing

Concept Serotonin-Release Assay

Concept Platelet-Activation Assay

Distinguished Non-Finalist

Presenter Organization University Hospitals/Case Western Reserve University

Presenting Author Cassandra L. Pasadyn

Track Adult

Keywords

heparin-induced thrombocytopenia

anti-PF4 antibody

serotonin release assay

postoperative thrombocytopenia

cardiopulmonary bypass

aortic valve replacement

pulmonary embolism

optical density

4T score

bivalirudin

Heparin-Induced Thrombocytopenia

4T Score

Anti-PF4/Heparin Immunologic Testing

Serotonin-Release Assay

Platelet-Activation Assay