Heparin-Induced Thrombocytopenia (HIT) Assays


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Subject: Heparin-Induced Thrombocytopenia (HIT) Assays

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  • HIT refers to thrombocytopenia that develops during or following the administration of heparin. There are various assays in use, none entirely satisfactory.

  • There are two groups of assays:

    • Immunologic: ELISA assays: use specific IgG antibodies; these assays have a high negative and positive predictive value.

    • Functional: Serotonin release assay, the gold standard for diagnosing HIT. An alternative functional assay is platelet aggregation standardized to use heparin as the aggregating agent.

  • Normal values

    • ELISA: negative if <0.4 optical density

    • Serotonin release assay (depends on the laboratory's own methodology): negative or positive


  • An HIT assay should be performed whenever HIT is clinically suspected.


  • ELISA requires well-trained, experienced technologists for accurate performance.

  • Serotonin release requires the use of radioactive materials. It is performed in only a few reference laboratories.