Medicine (Northern Health) - Theses

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Type: PhD thesis × Subject: Cardiovascular disease × Subject: COVID-19 × Subject: Fibrin generation × Start date: 2022 × End date: 2022 ×

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    Global coagulation assays in health and disease
    Lim, Hui Yin ( 2022)
    Thrombosis is a major global cause of morbidity and mortality, and predicting the risk of thrombotic and cardiovascular complications remain a challenge in modern medicine. Clinical surrogate markers and conventional coagulation testing, which only measures the time to start of clot formation, do not sufficiently predict individual risks. Global coagulation assays (GCA), which includes the assessment of the final products of the coagulation cascade, namely thrombin and fibrin, may be helpful adjunctive tools. Whilst GCAs have been more widely investigated in bleeding states, their role in thrombotic disorders is less well-established. In this thesis, we investigated the use of GCAs such as thromboelastography (TEG), calibrated automated thrombogram (CAT) and overall haemostatic potential assay (OHP) in healthy controls and a variety of disease states. These included thrombocytopenia and hypercoagulable states such as diabetes mellitus, plasma cell dyscrasia, the influence of hormone status, particularly oestrogen (transgender women on oestradiol therapy) as well as in coronavirus (COVID-19). We described the effect of basic demographic characteristics in healthy controls, particularly age and gender, on GCAs. Female controls demonstrated more hypercoagulable TEG and CAT parameters while age appeared to influence TEG, but not CAT parameters. Interestingly, healthy controls with “flattened” thrombin curves were associated with worse cardiovascular risk profile, possibly attributable to increased TFPI, suggesting a degree of compensation within the coagulation system in response to endothelial activation. Despite the common association of thrombocytopenia with bleeding, quantitative platelet counts do not always accurately predict this risk and thrombosis can occur despite thrombocytopenia. We reported while markedly thrombocytopenic patients demonstrated hypocoagulable profiles, patients with mild thrombocytopenia paradoxically appeared to have more hypercoagulable parameters. Overall, GCAs demonstrated the ability to help clinicians further discriminate thrombocytopenic patients. There is significant heterogeneity in the incidence and severity of diabetes-associated vascular complications, with limitations to clinical surrogate risk factors and glycated haemoglobin (HbA1c) as risk stratifiers. In addition to diabetes being a hypercoagulable state, particularly on TEG and OHP, we found several parameters to be associated with increased risk of diabetic complications and proposed a prediction model using a combination of GCA parameters (C-statistic 0.82). This is of clinical and prognostic significance as it may have utility in detecting early vascular complications and provide an indicator for early intervention. A larger prospective study with long-term follow-up of patient outcomes is ongoing. Monoclonal gammopathy of unknown significance (MGUS) is considered the clinically asymptomatic precursor of multiple myeloma although both forms are associated with an increased thrombotic risk. Contrary to expectations, there were no significant differences in the GCA parameters between patients with multiple myeloma and its MGUS precursor. However, patients who had arterial thrombotic events during the follow-up period demonstrated hypofibrinolysis based upon the OHP parameters. In exploring the role of hormonal influences on GCAs, we found that transgender women on oestradiol therapy demonstrated hypercoagulable TEG and CAT parameters as well as increased fibrinolysis compared to cisgender males. There was no significant difference seen relative to cisgender females, reflecting the shift towards feminisation. The route of estradiol delivery, its duration of use or the presence of concurrent anti-androgen therapy did not influence the GCA parameters. It is now well established that COVID-19 patients are susceptible to coagulopathy and thrombotic complications. We demonstrated marked impairment of fibrinolysis in COVID-19 patients compared to healthy controls and septic patients. Furthermore, patients with markedly increased OHP were more likely to require intensive care admission and ventilatory support. This suggests fibrinolysis may be an important therapeutic target in the management of one of the most challenging conditions we have faced in a century. Overall, we have shown that GCA appear to provide an advantage over conventional coagulation assays in the assessment of haemostatic function. While there are still limitations impeding the general applicability of these assays, further technical improvements may facilitate their introduction into clinical practice. Our data also suggest that these assays may have clinical utility in refining the thrombotic risk stratification. Further larger prospective studies to validate these findings are warranted.