The Ability of the Immucor IgG-Specific ELISA Optical Density Result to Predict SRA Positivity for the Diagnosis of Heparin-Induced Thrombocytopenia (HIT)

Document Type

Conference Proceeding

Publication Date

1-2018

Publication Title

American Journal of Clinical Pathology

Abstract

Introduction: Diagnosis of heparin-induced thrombocytopenia (HIT) usually requires detecting anti-platelet factor 4/heparin antibodies, particularly the IgG isotype (anti-PF4/H-IgG). In 2010, we developed a HIT diagnostic algorithm using the Immucor IgG-specific enzyme-linked immunosorbent assay (ELISA; PF4 IgG, Immucor GTI Diagnostics, Waukesha, WI) to screen for anti-PF4/H-IgG; if positive (optical density [OD] >0.4) or if significant clinical suspicion exists (regardless of OD) serum is sent to BloodCenter of Wisconsin (BCW) for the serotonin-release assay (SRA). Our ELISA reports include the likelihood (%) of a positive SRA based upon the ELISA OD, as follows: 0.40–0.99 (10%); 1.00–1.39 (20%); 1.40–1.99 (50%); >2.00 (100%). However, because these estimates were based on a previous study (J Thromb Haemost 2008;6:1304–12) using an “in-house” IgGspecific ELISA and SRA (both from McMaster Platelet Immunology Laboratory), our objective was to evaluate the relationship between the Immucor IgG-specific ELISA and the BCW SRA. Method: We identified paired ELISA and SRA results from 2012 to 2016; only cases where the anti-PF4/H-IgG and SRA samples were identically timed were included. The ELISA results with associated SRA were divided into the following OD categories: < 0.40; 0.40–0.99; 1.00–1.39; 1.40–1.99; >2.00. Results: A  total of 4038 ELISAs (3,644 patients) were reported with OD < 0.4 (n = 3,778), OD >0.4 (n = 260), and 171 exact-paired results. The percent likelihood of having a positive SRA was 0% (0/22) with OD < 0.40; 11.5% (8/69) with OD 0.40–0.99; 40% (10/25) with OD 1.00–1.39; 76.3% (29/38) with OD 1.40–1.99; and 82.4% (14/17) with OD >2.00. Conclusions: A  negative Immucor IgG-specific ELISA predicts for a negative SRA. As expected, increasing OD values increase the likelihood of SRA positivity. However, with ELISA ODs >1.0, the predictive relationship between the Immucor IgG-specific ELISA and the BCW SRA differs somewhat from the predictive relationship for the two McMaster assays. We conclude that important differences in the ELISA-SRA relationship can exist among different anti-PF4/H-IgG ELISAs and different SRAs.

Volume

149

Issue

Suppl 1

First Page

S30

Comments

American Society for Clinical Pathology (ASCP) Annual Meeting, November 2-5, 2017, Kissimmee, FL

Last Page

S30

DOI

10.1093/ajcp/aqx116.068

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