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    HIT Expert Probability (HEP) Score for Heparin-Induced Thrombocytopenia

    Pre-test clinical scoring model for HIT based on broad expert opinion.
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    When to Use
    Pearls/Pitfalls
    Why Use

    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.

    Thrombocytopenia Features
    Typical
    Rapid
    <30%
    -1
    30-50%
    +1
    >50%
    +3
    ≤20
    -2
    >20
    +2
    No
    0
    Yes
    +3
    No
    0
    Yes
    +2
    No
    0
    Yes
    -1
    Other Causes of Thrombocytopenia
    No
    0
    Yes
    -1
    No
    0
    Yes
    -1
    No
    0
    Yes
    -2
    No
    0
    Yes
    -2
    No
    0
    Yes
    -2
    No
    0
    Yes
    -1
    No
    0
    Yes
    +3

    Result:

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    Next Steps
    Evidence
    Creator Insights

    Critical Actions

    • Consider using the 4Ts scoring system in conjunction with the HEP score as an alternative evaluation tool prior to time-consuming antibody testing for HIT or empiric substitution of heparin for another anti-coagulant.
    • Consider further laboratory evaluation for HIT or switching to a non-heparin derived anti-coagulant in those patients that are above the screening threshold for HIT based on their HEP score.
    • Larger studies of the HEP score are likely necessary prior to broader independent implementation.
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    About the Creator
    Dr. Adam Cuker
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