Is viscoelastometric testing a good tool to assess hemostasis of COVID-19 patients?

Background : Infection by SARS-CoV-2 is associated with a high risk of thrombosis. The laboratory documentation of hypercoagulability and impaired fibrinolysis remains a challenge. Aims : Our main aim was to assess the potential usefulness of viscoelastometric testing (VET) to predict thrombotic events in COVID-19 patients according to the literature. Our secondary aims were: (i) to analyze the impact of anticoagulation and the methods used to neutralize heparin, (ii) to see whether maximal clot mechanical strength brings more information than Clauss fibrinogen, and (iii) to point out results from studies with enhanced fibrinolysis modified tests. Methods : We performed a systematic search in PubMed and Scopus databases, until December 31st, 2020 (Figure 1). VETs methods and parameters, as well as patients ' features and outcomes were extracted. Results : VET was performed for 1063 patients (893 ICU and 170 non-ICU, n = 44 studies). There was a huge heterogeneity concerning study design, the VET device (ROTEM, TEG, Quantra and ClotPro) and reagents (with non-systematic use of heparin neutralization by heparinase and/or polybrene), timing of assay, and definition of hypercoagulable state. The common findings were an increased clot mechanical strength mainly due to an excessive fibrinogen component with impaired to absent fibrinolysis, more conspicuous in the presence of an added plasminogen activator. This profile was associated with an uncontrolled thrombin generation despite a standard thromboprophylaxis. However, only 4 studies out of 16 that addressed this point found an association of VETs with thrombotic events. Functional fibrinogen assessed by VET showed a variable correlation with Clauss fibrinogen. Abnormal VET pattern tended to normalization after an enhancement in thromboprophylaxis. Notably, only 4 studies out of 25 using ROTEM reported data where heparin is neutralized by heparinase (HEPTEM). Conclusions : The heterogeneity among VET studies and small sample sizes do not permit to point out an association between the illdefined hypercoagulable state and thrombotic events.