What is the role of functional assays in the workup of heparin-induced thrombocytopenia (HIT)?

Updated: Sep 10, 2021
  • Author: Sancar Eke, MD, FASN; Chief Editor: Srikanth Nagalla, MD, MS, FACP  more...
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Functional assays include the heparin-induced platelet aggregation assay (HIPA) and the serotonin release assay (SRA). Most laboratories that perform functional testing use HIPA, which is highly specific but which is also reported to be less sensitive than SRA. The availability of SRA is largely restricted to centers where HIT is a focus of research.

The SRA is based on HIT antibodies causing platelets to aggregate and release serotonin. For the test, platelets of normal donors are radiolabeled with carbon 14 (14C)-serotonin and are washed; these platelets are then mixed with patient serum, along with low (therapeutic) and high heparin concentrations. The test is considered positive if the sample causes a greater than 20% serotonin release at a (therapeutic) dosage of 0.1 U/mL heparin.

The14C-SRA is considered the "gold standard" assay for the detection of heparin-dependent antibodies in heparin-induced thrombocytopenia (HIT). [53] The sensitivity of SRA has ranged from 69% to 94%, and its specificity of SRA may be as high as 100%. [54, 55, 56]

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