Abstract Number: LPB0013
Meeting: ISTH 2021 Congress
Background: Heparin-induced thrombocytopenia (HIT) is a clinicopathologic diagnosis that can result in thrombotic complications in patients receiving heparin thromboprophylaxis. COVID-19−associated coagulopathy was recognized internationally in February 2020 and is now considered a prothrombotic state; multiple scientific societies recommend thromboprophylaxis in hospitalized COVID-19 patients. The major thromboprophylaxis agents are low molecular-weight heparin (LMWH) and unfractionated heparin (UFH). Given this increased exposure to heparins and the thrombo-inflammatory nature of COVID-19, we investigated whether there was a change in positive rates of HIT antibody tests.
Aims: To determine if functional and antigenic HIT antibody positivity was affected by the COVID-19 pandemic
Methods: We conducted a retrospective review of HIT IgG enzyme-linked immunosorbent assay (ELISA) and serotonin release assay (SRA) results from February to December of 2019 and the corresponding months in 2020. Positivity for HIT IgG ELISA was defined as an optical density >0.300 per manufacturer instructions. SRA positivity was defined as ≥20% release at low heparin concentration that coincided with >50% reduction of serotonin release at high heparin concentration. Median monthly positivity rates of 2019 and 2020 were compared for HIT IgG ELISA, and for LMWH and UFH SRA. Nonparametric testing for statistical significance was performed by Mann-Whitney U testing (two-tailed).
Results: From 2019 to 2020, testing increased for LMWH SRA (16.7%), UFH SRA (11.2%), and HIT IgG ELISA (56.1%), indicating either possible increased exposure to heparin or suspicion for HIT. The median monthly percent positivity did not significantly differ between 2019 and 2020 for either SRA. However, the median monthly percent positivity was significantly lower in 2020 than in 2019 for IgG ELISA (See Table).
| HIT Assay | 2019 | 2020 | P value |
| LMWH SRA | 12.9 % (7.3 – 17.9%) | 13.5 (7.9 – 18.8%) | 0.1499 |
| UFH SRA | 8.1 % (6.4-11.0%) | 8.8% (6.8 – 10.7%) | 0.8415 |
| HIT IgG ELISA | 17.6 % (14.6 – 21.1%) | 14.9% (10.4 – 17.7%) | 0.0048 |
Median (5th and 95th Percentile) Monthly Positivity Rates for HIT IgG ELISA and UFH and LMWH SRA in 2019 and 2020
Conclusions: Exposure to either LMWH or UFH during the COVID-19 pandemic in 2020 was not associated with increased SRA positivity, and HIT IgG ELISA positivity decreased, despite increased clinical suspicion for HIT during 2020.
To cite this abstract in AMA style:
Wong E, Worfolk L, Noh L, Wu W, Sahud M, Racke F, Dlott J. Evaluation of Heparin-induced Thrombocytopenia Before and during the COVID-19 Pandemic at a US National Reference Laboratory [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/evaluation-of-heparin-induced-thrombocytopenia-before-and-during-the-covid-19-pandemic-at-a-us-national-reference-laboratory/. Accessed June 25, 2022.« Back to ISTH 2021 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/evaluation-of-heparin-induced-thrombocytopenia-before-and-during-the-covid-19-pandemic-at-a-us-national-reference-laboratory/