HITTING the Diagnosis: Testing for Heparin-Induced Thrombocytopenia in Cancer Patients.

Objectives: To evaluate the use of a pretest probability score (4Ts score) in cancer patients to guide ordering of laboratory screening tests for heparin-induced thrombocytopenia (HIT).

Methods: A retrospective chart review was conducted for patients (n = 140) in whom laboratory testing for HIT was requested. 4Ts scores were calculated and correlated with heparin-endogenous platelet factor 4 antibody enzyme-linked immunosorbent assay (ELISA) test results.

Results: All patients with a high pretest probability of HIT (4Ts score = 6-7) had positive ELISA results, compared to 26.1% of patients with intermediate (4Ts score = 4-5) and 4.3% of patients with low (4Ts score ≤3) pretest probability. No patients with 4Ts scores of 2 or less had positive ELISA results.

Conclusions: HIT can be ruled out in cancer patients (negative predictive value and sensitivity = 100%) with low pretest probability, defined by 4Ts scores of 2 or less, significantly reducing the need for laboratory testing in this patient population.