The platelet serotonin‐release assay

Few laboratory tests are as clinically useful as The platelet serotonin‐release assay (SRA): a positive SRA in the appropriate clinical context is virtually diagnostic of heparin‐induced thrombocytopenia (HIT), a life‐ and limb‐threatening prothrombotic disorder caused by anti‐platelet factor 4 (PF4)/heparin antibodies that activate platelets, thereby triggering serotonin‐release. The SRA's performance characteristics include high sensitivity and specificity, although caveats include indeterminate reaction profiles (observed in ∼4% of test sera) and potential for false‐positive reactions. As only a subset of anti‐PF4/heparin antibodies detectable by enzyme‐immunoassay (EIA) are additionally platelet‐activating, the SRA has far greater diagnostic specificity than the EIA. However, requiring a positive EIA, either as an initial screening test or as an SRA adjunct, will reduce risk of a false‐positive SRA (since a negative EIA in a patient with a “positive” SRA should prompt critical evaluation of the SRA reaction profile). The SRA also provides useful information on whether a HIT serum produces strong platelet activation even in the absence of heparin: such heparin‐“independent” platelet activation is a marker of unusually severe HIT, including delayed‐onset HIT and severe HIT complicated by consumptive coagulopathy with risk for microvascular thrombosis. Am. J. Hematol. 90:564–572, 2015. © 2015 Wiley Periodicals, Inc.

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