Serotonin Release Assay (SRA)

 The SRA is a diagnostic test for Heparin-Induced Thrombocytopenia (HIT). The test measures the ability of a patient's serum, that putatively contains an antibody to the heparin-platelet factor 4 (PF4) complex, to activate normal donor platelets.

In this test, normal platelets obtained from a donor previously shown to be reactive to a panel of heparin-PF4 antibodies, are incubated with radiolabeled serotonin. The labeled platelets are then incubated with the patient's serum in the absence and presence of heparin (in therapeutic and supratherapeutic concentraions). Platelet activation is measured by the release of radioisotope from the platelets.

For a test to be reported as positive, there must be at least 20% of the radioactivity released in the presence of therapeutic heparin levels ().1 U/ml), and release must be substantially reduced in the tube containing high (100 U/ml) heparin.

 The Florida Hospital Center for Hemostasis and Thrombosis is one of the few labs in the U.S. that performs this test. Because of the time-consuming nature of the assay, we will only perform it if an ELISA-based test for heparin-PF4 antibodies has already been shown to be positive.

The SRA is typically performed weekly by the research staff of the Thromobosis Research Unit. The assay is not approved for clinical use by the FDA and is therefore marked as "Research Use Only".