Prediction of Heparin Induced Thrombocytopenia (HIT) Using a Combination of 4Ts Score and Screening Immune Assays

• Main Authors: Rajat Thawani MD, Srikant Nannapaneni MD, MS, Vivek Kumar MD, Phone Oo MD, Michael Simon MD, Anna Huang MPHc, Ishan Malhotra MD, Yiqing Xu MD, PhD
• Format: Article
• Language: English
• Published: SAGE Publishing 2020-09-01
• Series: Clinical and Applied Thrombosis/Hemostasis
• Online Access: https://doi.org/10.1177/1076029620962857

Clinical assessment (4Ts) followed by testing for Heparin/platelet factor 4 (HPF4) antibody in intermediate and high risk patients is the standard algorithm of pretest for Heparin induced thrombocytopenia (HIT), and the diagnosis is confirmed by serotonin releasing assay (SRA) in those who have positive antibodies. We conducted a retrospective analysis in a cohort of patients treated in a community hospital who had HIT antibody test by either ELISA or a rapid Particle Immunofiltration Assay (PIFA), regardless of their 4Ts scores. Among 224 patients, 17 had HIT. The PPV for those with a 4 T score ≥4 was 10.4%, which misdianosed 3 patients with HIT who tested positive for antibodies. Combining 4 T score ≥4 AND positive HIT antibody showed a PPV of 20.3% and a sensitivity of 70.6%, misdiagnosing 5 HIT patients. Using 4Ts ≥4 OR positive HIT antibody showed 100% sensitivity and 100% negative predictive value (NPV). The ELISA test had 100% sensitivity and 100% NPV, while the PIFA test missed 2 HIT patients, with sensitivity of 60% and NPV of 96.7%. Our results suggest that SRA testing should be conducted if a patient presents with a 4 T score ≥4 OR a positive HIT antibody, and antibody tests should be conducted for every patient suspected of HIT.