ABSTRACT
Background: Increased von Willebrand factor (VWF) is common in COVID-19 infection. vWF levels are reported at levels where pre-dilution of samples is required. The assumption is that such dilutions respond linearly across the measurement range, and that this response is consistent across patient subgroups. ADAMTS13 levels have also been reported as reduced in those most severely affected. The interaction of these biomarkers has potential consequences to understanding pathophysiology of COVID-19. Aim(s): To investigate the linearity of dilution of high VWF levels in patients with COVID-19 To compare the response in those mildly affected to those requiring more intensive therapy Methods: This is a laboratory bases study investigating a convenience sample of fifty age and gender matched patients hospitalised during the first wave of the COVID-19 pandemic (March to June 2020). Patients had been hospitalised for >24 hours before enrolment. Platelet RiCof activity was using the VW Select assay (BioData Corps, Horsham, USA). Dilutions were made using assay buffer provided in the kit. Data was collected in Microsoft Excel, before being analysed in both Microsoft Excel and the statistical programming environment R (R Core Team (2021)). Result(s): The findings of Mancini et al were replicated here in that locale of patient admission was associated with a statistically significant reduction of ADAMTS13 activity (ITU mean 60.21 v non-ITU mean 92.23). The activity of ADAMTS13 remained within what would be a reference range for diagnosis of TTP. VWF activity by Platelet RiCof was markedly raised. Serial dilution of samples demonstrated non-parallelism, the response being most marked in severely affected patients. Conclusion(s): Very high VWF levels disrupt the balance with mildly reduced ADAMTS13. In severe COVID-19 infection, the effect manifests as non-parallelism in platelet RiCof parameters. This calculated parameter classifies patients both by presence and severity of disease across all parameters in the platelet Ristocetin CoFactor assay. (Figure Presented).
ABSTRACT
Background: Critically ill patients infected with the SARS-CoV- 2 virus are known to have a coagulopathy with a risk of thrombosis due to endothelial activation and systemic inflammation. Veno-venous extracorporeal membrane oxygenation (VV ECMO) is recommended by the World Health Organisation (WHO) as a supportive therapy for patients with severe COVID-19 infection when conventional ICU methods have proven ineffective. VV ECMO comes with haematological complications, including loss of high molecular weight von Willebrand factor multimers, consumption of clotting factors and premature activation of platelets. Laboratory methods to characterise haemostasis in these patients are required and may be clinically useful in predicting clinical outcome. Aim(s): Can non-standard methods provide clinically meaningful results in COVID-19 positive patients supported by VV ECMO? Methods: Tissue plasminogen activator and von Willebrand factor were quantified via Abcam SimpleStep ELISA in VV ECMO supported Covid-19 patients and normal controls. Fibrinogen antigen concentration was quantified via Liaphen Fibrinogen Antigen assay in VV ECMO supported Covid-19 patients and normal controls. VW Select ristocetin cofactor assay was used to assess von Willebrand Factor activity in VV ECMO supported COVID-19 patients. Result(s): Tissue plasminogen activator and von Willebrand factor concentrations are significantly increased in COVID-19 patients supported by VV ECMO compared to healthy controls, which reflects endothelial damage displayed in critically unwell COVID patients. Fibrinogen levels were not significantly different between the two patient groups. The VW Select ristocetin cofactor assay detected patients with low vWF activity that would have otherwise been overlooked by standard methods. Conclusion(s): Non-conventional laboratory methods can be used to represent the extent of endothelial damage and risk of bleeding in patients who are COVID-19 positive and anticoagulated on VV ECMO support. The assays help to characterise pathology of COVID-19 used in conjunction with standard tests by providing clinically relevant results. (Figure Presented).
ABSTRACT
Background: Argatroban is a direct thrombin inhibitor currently licenced in the UK and USA for treatment of Heparin Induced Thrombocytopenia (HIT) and has been utilised as an alternative anticoagulant for critically ill COVID-19 patients. UK and US guidelines recommend Argatroban monitoring via activated partial thromboplastin time (aPTT), in critically ill patients, recommending ratios of between 1.5-3 times patient's baseline, without exceeding 100 s. This guidance is based on spiked pooled platelet poor plasma with increasing concentrations of Argatroban. Aim(s): * Does the aPTT demonstrate suitable linearity for Argatroban monitoring? * Are readily available alternatives more useful to indicate extent of Argatroban anticoagulation? Methods: From May to July 2021, 97 residual blood samples from 12 patients receiving Argatroban were processed for HemosIL APTT-SS, Thrombin time, Argatroban, and dilute thrombin time using ACL-TOP750 (Werfen, Bedford, USA). Performance was compared to commercial calibrators, across a therapeutic range from 0-2.08 mug/ml mimicking spiked plasma. Result(s): * No linearity was observed between Argatroban concentration and aPTT ratio (R2 value of 0.0778) in critically ill patient plasma compared to linearity for APTT ratios (R2 value of 0.9346) in commercial calibrators * Thrombin time produced good linearity with Argatroban (R2 value of 0.8473). Non-specific clot curve kinetic issues and exceeding acquisition times were noted. * Dilute thrombin time produced very good linearity with Argatroban (R2 value of 0.9443) Conclusion(s): In critically ill patients, aPTT ratio lacks a demonstrable linear response, unlike spiked and commercial plasmas. Non linearity is most likely due to other effects on the aPTT than Argatroban alone. 10.3% of patients exceeded an Argatroban concentration of 2.08 mug/ml with an aPTT ratio within guideline quoted ranges. Thrombin time and dTT demonstrated linearity. However, the thrombin time had non-specific clot curve kinetic abnormalities and some results exceeded acquisition time. No issues were seen with dilute thrombin time.