Q: What is considered to be the gold assay for Heparin Induced Thrombocytopenia (HIT)?


Answer: Serotonin release assay 

The 5 components required to do this test are

• Donor platelets 
• 14C-serotonin radiolabel
•  Patient's serum 
•  Heparin at therapeutic concentrations (0.1 units/mL)
•  Heparin at excessive concentrations (100 units/mL)

First, platelets from normal donors are radiolabeled with 14C-serotonin. Incubation is done with patient serum plus heparin at therapeutic as well as at excessive concentrations. A positive test is the release of 14C-serotonin when therapeutic heparin concentrations are used, but not with excessive heparin concentrations. This sounds odd but it reflects the fact that the binding of HIT antibodies is only seen at certain ratios of heparin to PF4.