Abstract Number: PB0686
Meeting: ISTH 2020 Congress
Background: Serotonin release assay (SRA), the gold standard for diagnosis of heparin-induced thrombocytopenia (HIT), is mostly performed in reference laboratories with unacceptable turn-around-times (TAT). HIT- ELISAs are performed in most laboratories, usually with 24-hour TAT. HIT IgG antibody is more specific for HIT-thrombosis; IgA and IgM antibodies are not pathogenic. Recently, a fully automated, rapid assay latex enhanced immunoassay (LIA) (HemosIL, HIT-Ab (PF4-H), Instrumentation Laboratory, Bedford, MA) was FDA approved, which replaced our manual ELISA (PF4 IgG assay, Immucor, Waukesha, WI). LIA-positive samples reflex to SRA (Versiti, Milwaukee, WI).
Aims: We evaluated performance characteristics of LIA test compared with SRA and clinical outcome.
Methods: We reviewed all 65 positive LIA tests (≥ 1 U/ml per manufacturer) between October 2017 and September 2019. Fifty-nine tests from 52 patients had corresponding SRA; 44 had clinical data available. Statistical analyses were performed using Stata and Microsoft Excel.
Results: All patients had a 4Ts score ≥ 3. LIA had a 60% false positive rate (31 of 52 patients negative by SRA); positive predictive value (PPV) was 0.40 (95% CI 0.27, 0.54). Seven SRA-negative patients had repeat SRAs; 2 (29%) became positive. One of these positives had initial LIA of 1.7 U/ml and repeat result of 1.4 U/ml after 5-day interval. The second patient had initial and repeat LIA of both 7 U/ml at 6-day interval. Of the 28 SRA-negative patients with clinical data, 25 (89%) were treated with alternate anticoagulation.
Conclusions: Test performance in our institution was concordant with the package insert PPV. The high false positive rate (PPV 0.40) may be due to detection of IgM or IgA HIT antibodies that do not activate platelets. However, LIA shows increased sensitivity, becoming positive before SRA as demonstrated in two cases. To reduce false positives by LIA and its attendant treatment consequences, we are revising our testing algorithm (Figure 1).
To cite this abstract in AMA style:
Welder D, Compton F, De Simone N, Nagalla S, Rambally S, Webb C, Sarode R. Rapid Latex Enhanced Immunoassay (LIA) for Heparin Induced Thrombocytopenia and False Positivity [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/rapid-latex-enhanced-immunoassay-lia-for-heparin-induced-thrombocytopenia-and-false-positivity/. Accessed March 21, 2024.« Back to ISTH 2020 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/rapid-latex-enhanced-immunoassay-lia-for-heparin-induced-thrombocytopenia-and-false-positivity/