HIT Expert Probability (HEP) Score for Heparin-Induced Thrombocytopenia
The heparin-induced thrombocytopenia expert probability (HEP) score is a tool that can potentially aid in diagnosing patients with suspected HIT, and to avoid expensive HIT workups in some patients.
The HIT Expert Probability (HEP) Score is a tool developed based on broad expert opinion to help clinicians rule out HIT.
- Eight clinical features potentially important in the diagnosis of HIT identified via literature review were incorporated into a questionnaire and distributed to independent HIT experts that regularly diagnose and treat HIT.
- Clinicians then weighed each feature on a scale of -3 to 3 with more positive numbers arguing in favor of HIT.
- Median weights were then incorporated into a pre-test probability model, the HEP score.
- Score was then prospectively applied to fifty consecutive patients referred to a single reference laboratory for HIT testing.
- HIT was diagnosed by consensus of three independent HIT expert adjudicators reviewing the clinical information and lab results including polyspecific HIT antibody ELISA and in-house SRA.
- Study found that a HEP score cut off of 2 would lead to 100% sensitivity and 60% specificity while a cut off of 5 would maximize sensitivity/specificity at 86% and 88%, respectively, in the cohort of patients analyzed. This was superior to the 4Ts for HIT Score.
Points to keep in mind:
- Validation study was very small at 50 patients, highly heterogeneous, and all done at a single large academic health care system.
- All determinations of HIT were done based on chart review.
- Score was derived based purely on expert opinion and the confirmatory diagnosis of HIT was also based on the consensus of an expert panel.
- A subsequent small (47 patients) retrospective study comparing the performance of the 4T’s scoring system vs HEP in suspected HIT patients, using a positive HPA as the gold standard for diagnosis of HIT, found no statistically significant difference in the diagnostic performance of the scores. It also demonstrated only a 70% sensitivity for the diagnosis of HIT at the previously proposed HEP score cut-off of 2.
- There are no large scale or prospective studies validating the HEP score.
The work-up for HIT is time-consuming and expensive. The HEP score could be used as a tool to avoid initiating work-up for HIT and/or empiric substitution of heparin for another anti-coagulant.