Anti-platelet factor 4 testing for heparin-induced thrombocytopenia: Assessing the indication for its use for quality...

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.

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.

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.

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.