Multi-Year Study of Unfractionated Heparin Serotonin Release Testing at a Large U.S. Reference Laboratory

Abstract Introduction: The serotonin release assay (SRA) is a functional assay for the detection of heparin-induced thrombocytopenia (HIT). Laboratory practice suggests that it is important to test several low doses of unfractionated heparin (UFH), followed by suppression at a high dose (100 U/mL) of UFH to demonstrate the specificity for HIT. However, little is known of the demographic associations with UFH SRA testing at a large reference laboratory. Purpose: To characterize the population characteristics of UFH SRA testing at a large US reference laboratory Methods: We performed a multi-year retrospective review of positivity rates among adults (n=63,651) and children ( 50% suppression of release at high dose (100 U/mL) of UFH. Indeterminant results were defined by ≥20% release at either low dose of UFH, but without >50% suppression at the high dose of UFH. A negative result was defined as Results: Over the study period, SRA testing included 63,051 adults and 233 children who encompassed 99.5% and 0.5% of the total population tested, respectively. Over the years studied, the positivity rate increased steadily from 4.08% to 7.50%, which was seen in adults but not in children. For positive SRA results, the ratio of male to female was nearly identical to the overall male to female ratio (55:45) in the tested population. In additional, no seasonal variation was noted. Yearly median percent positive, indeterminant, and negative SRA results were 5.42%, 3.32%, and 89.73%, respectively, for adults, and 1.96%, 6.52%, and 93.48%, respectively, for children, with children having significantly lower SRA positivity than adults (p Among positive tests in adults, we examined the results by level of low dose UFH: the median positivity rates were 3.46% for 0.1 U/mL only, 1.03%, for 0.5 U/mL only, and 95.89% for both 0.1 and 0.5 U/mL UFH. In contrast, children demonstrated positive tests only when both 0.1 and 0.5 U/mL UFH results were positive. These children (n=6, median age 14 yrs with range 3 to 15 yrs) demonstrated median serotonin release of 81% and 77% at 0.1 and 0.5 U/mL of UFH, respectively, which was not significantly different from each other and similar to the corresponding adult positive (both 0.1 and 0.5 U/mL UFH) SRA population. Conclusions: Adults have a higher prevalence of SRA testing compared to children and have median positivity rates that are significantly higher (2-3 fold).The consistent increase in yearly percentage of positive tests, suggests improved clinical screening and/or diagnostic pathways for HIT. Testing was not influenced by gender or seasonal variation. To our knowledge, these findings provide, for the first time, a detailed picture of SRA testing from a large US reference laboratory. Disclosures Wong: Quest Diagnostics: Employment, Other: stock . Sahud: Quest Diagnostics: Consultancy. Noh: Quest Diagnostics: Employment. Aboueyada: Quest Diagnostics: Employment. Frock: Quest Diagnostics: Employment. Haley: Quest Diagnostics: Employment. Wu: Quest Diagnostics: Employment. Dlott: Quest Diagnostics: Employment, Other: stock.