Validation of Heparin-Induced Thrombocytopenia Risk Stratification Tools in Post-Surgical Patients

INTRODUCTION: Heparin induced thrombocytopenia (HIT) is a potentially life threatening immune-mediated adverse event occurring in 0.1-3% of post-surgical cardiovascular (CV) patients. The 4T score is the gold standard risk stratification tool to assess the likelihood of HIT in medical patients with limited applicability in post-surgical CV patients who commonly experience post-operative thrombocytopenia. We aimed to test the Cardiopulmonary Bypass (CPB) and HIT Expert Probability (HEP) scores to better evaluate the risk of HIT in these patients.

METHODS : This IRB approved retrospective cross-sectional study compared the 4T, CBP, and HEP scoring tools in post-surgical CV patients. Eligible patients were identified by lab reports of Enzyme Linked Immunosorbent Assay (ELISA) and/or Serotonin Release Assay (SRA) tests. Patients included were aged 18-89, admitted to the Cardiovascular Intensive Care Unit (CVICU) or the Coronary Care Unit (CCU), with post-operative thrombocytopenia and suspected HIT. HIT positive was defined as an ELISA optical density (OD) >1 with evidence of thromboembolism or positive SRA. Descriptive statistics characterized the predictive value of the scoring tools when compared to corresponding test results.

RESULTS: A total of 291 patients received ELISA and/or SRA testing between January 2019 - July 2021 with 137 patients meeting criteria. Of the 137 patients, 126 were HIT negative and 11 were HIT positive. There was no difference in age, gender, BMI, baseline platelet counts or nadir in both groups. A high 4T score (>6) was significantly more likely in the HIT positive group (11% vs. 64%, p< 0.0001). The CPB score of ≥2 was significantly different (33% vs. 75%, p=0.017). The HEP score of ≥2 had a statistically higher predictability (57% vs. 100%, p=0.0006). The overall sensitivity and specificity of the CPB were 33 and 75 and HEP scores were 57 and 100. The median OD in the HIT negative and positive arms were 0.09 and 1.28, p< 0.0001, respectively.

CONCLUSIONS: Our findings support the utilization of the HEP scoring tool in identifying HIT in our CV surgery population. A high 4T Score continues to hold a significant differentiation value and utility can still be considered. Increasing the OD threshold to >1 strengthens the concern for HIT and warrants confirmatory testing with the SRA.