Demand on-demand testing for the diagnosis of heparin-induced thrombocytopenia

In theory,most laboratory tests for immune heparin-induced thrombocytopenia (HIT) can beperformedwithin a fewhours of blood sample acquisition. But for the most common type of test performed – the platelet factor 4 (PF4)-dependent enzyme-linked immunosorbent assay (ELISA) – the blood samples are almost always tested in batches, at most once-daily (and often not on weekends), and so results are frequently not available to the clinician until 1–4 days later. More definitive tests for detecting HIT antibodies (with greater diagnostic specificity), such as certain platelet activation assays, are performed by relatively few centers, and thus there is an additional time delay that reflects sample delivery to a different facility that could even be in another state or province. Even at my own medical center, with an excellent assay for HIT (the platelet serotonin-release assay), testing is performed just twice-weekly (Tuesdays and Thursdays, with results reported Wednesdays and Fridays, respectively), meaning that a turnaround of up to several days is common [1]. But some PF4-dependent immunoassays have been specifically designed for rapid turnaround, defined as 30 min or less [2]. Moreover, such “on-demand” tests are engineered for evaluation of single blood specimens. Thus, if such an assay is available on-site at a laboratory located within (or near) a clinical institution, there is the prospect for a speedy test result within a relatively short period of time. Rapid, ondemand assays for HIT that have been developed include automated tests requiring proprietary machines, such as the HemosIL® HITAb(PF4\\H) (performed using an ACL TOP® hemostasis analyzer; Instrumentation Laboratory, Bedford, MA) [3,4], the HemosIL AcuStar HITIgG(PF4\\H) and HemosIL AcuStar HIT-Ab(PF4\\H) (IgG-specific and polyspecific fully-automated chemiluminescence assays, respectively, using the ACL AcuStarTM hemostasis testing system) [4,5], the particle gel immunoassay (PaGIA; H/PF4-PaGIA®, Bio\\Rad,Marne La Coquette, France), using standard blood bank centrifugation equipment [6,7], and the lateral flow immunoassay (STic Expert® HIT, Diagnostica Stago, Asnières sur Seine, France) [8,9]. (Although another on-demand assay – the particle immunofiltration assay (PIFA®; Akers Biosciences, Thorofare, NJ) – is marketed, this test has poor operating characteristics [10], and its use for HIT diagnosis is problematic [11].) In this issue of Thrombosis Research, Caton and colleagues [12] have performed a literature review and conducted semi-structured interviews and surveys evaluating various diagnostic and treatment strategies for different HIT laboratory tests. They then modeled the frequency and overall costs associated with various adverse HITrelated outcomes, such as bleeding and thrombosis, for different test approaches. The authors concluded that “modeling estimated more HITrelated [adverse] outcomes for patients maintained on heparin whilst awaiting test results and patients switched onto replacement anticoagulant therapy awaiting test results, compared with on-demand testing