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. 2025 Nov 19;164(5):778-784.
doi: 10.1093/ajcp/aqaf102.

Anti-platelet factor 4 testing for heparin-induced thrombocytopenia: Assessing the indication for its use for quality improvement as a patient safety measure

Hisham F Bahmad  1 , Ruben Delgado  1 , Richard R Pacheco  2 , Kei Shing Oh  1 , Lorena P Rojas Gomez  3 , Esha Vallabhaneni  3 , Roshanak Azimi  1 , Vathany Sriganeshan  1   4 , Lydia Howard  1   4 , Robert Poppiti  1   4 , Sarah Alghamdi  1   4
Affiliations

Anti-platelet factor 4 testing for heparin-induced thrombocytopenia: Assessing the indication for its use for quality improvement as a patient safety measure

Hisham F Bahmad et al. Am J Clin Pathol. .

Abstract

Objective: To assess the appropriateness and clinical indication of ordering the heparin-induced thrombocytopenia (HIT) platelet factor 4 (PF4) tests (based on the 4T score) for the diagnosis of HIT.

Methods: We retrospectively analyzed 261 PF4/polyvinylsulfonate (PVS)-enzyme-linked immunosorbent assay (ELISA) tests performed for 261 patients between January 2020 and June 2022. Patients were divided into 2 groups: 4T score less than 4 (unindicated HIT test requests) and 4T score of 4 or more (appropriately indicated HIT test requests). Clinical characteristics, test results, and treatment decisions were compared between groups.

Results: Only 136 (52.11%) of 261 tests were indicated by a 4T score or 4 or higher, whereas 125 (47.89%) of 261 tests were performed in low-probability patients (4T score <4). The PF4/PVS-ELISA positivity rate did not differ significantly between groups (11.03% vs 5.6%, P = .125). Patients with indicated testing had higher baseline platelet counts, longer time to platelet drop, and a greater percent drop in platelets (all P < .001). Among the 22 PF4/PVS-ELISA positive cases, only 10 had serotonin release assay (SRA) testing performed, of which 2 were SRA-positive. Among patients with low clinical probability, 75.20% (94/125) had heparin discontinued, despite the minimal risk.

Conclusions: Most HIT testing was inconsistent with guideline recommendations of the American Society of Hematology. Overtesting may lead to unnecessary anticoagulation, and undertreatment may have occurred in high-risk cases. These findings underscore the need for improved implementation of 4T-based decision tools to guide HIT evaluation and treatment.

Keywords: 4T score; PF4/PVS-ELISA; heparin; heparin-induced thrombocytopenia; quality improvement; serotonin release assay.

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