• Chee M Chan, Christian J Woods, Theodore E Warkentin, Jo-Ann I Sheppard, and Andrew F Shorr.
• Chest. 2015 Jul 1;148(1):55-61.

BackgroundHeparin-induced thrombocytopenia (HIT) is a serious complication of heparin utilization. An enzyme-linked immunosorbent assay (ELISA) is usually performed to assist in the diagnosis of HIT. ELISAs tend to be sensitive but lack specificity. We sought to use a new cutoff to define a positive HIT ELISA.MethodsWe conducted a prospective observational study of hospitalized patients undergoing ELISA testing. All patients who underwent ELISA testing were eligible for inclusion (n = 496). Irrespective of the results, all subjects had confirmatory testing with a serotonin release assay (SRA). We compared a threshold optical density (OD) > 1.00 to the current definition of a positive ELISA (OD > 0.40) as a screening test for a positive SRA. We used sensitivity, specificity, and area under the receiver operating curve to determine whether an OD > 1.00 would improve diagnostic accuracy for HIT.ResultsThe SRA was positive in 10 patients (prevalence, 2.0%). Adjusting the definition of a positive HIT ELISA to > 1.00 maintained the sensitivity and negative predictive value at 100% in the cohort. The positive predictive value of the higher cutoff OD was more than triple the positive predictive value of an OD > 0.40 (41.7% vs 13.3%). No patient with a positive SRA had an OD measurement ≤ 1.00.ConclusionsIncreasing the OD threshold enhances specificity without noticeably compromising sensitivity. Altering the definition of the HIT ELISA could prevent unnecessary testing and/or treatment with non-heparin-based anticoagulants in patients with possible HIT.Trial RegistryClinicalTrials.gov; No.: NCT00946400; URL: www.clinicaltrials.gov.

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