New diagnostic approaches for venous thromboembolism and thrombophilia

Background: Venous thromboembolism is a serious disease comprising both pulmonary embolism and deep vein thrombosis. Venous thromboembolism causes considerable mortality and morbidity, with residual symptoms such as pulmonary hypertension and post thrombotic syndrome. Current assays for venous thromboembolism and the predisposition to develop venous thromboembolisms (thrombophilia) can only reflect a fragment of the complicated hemostatic processes. This thesis evaluates the usefulness of current and emerging hemostatic assays that reflect several aspects of the hemostatic process. Increased diagnostic specificity would enable better diagnosis and risk stratification of patients with venous thromboembolism. Improved biomarkers for venous thromboembolism and thrombophilia have the potential to prevent major morbidity and mortality by guiding treatment and prophylaxis to the right patients at the right time.

Aim: The aim of this project was to investigate assays that could improve the care for patients with suspected venous thromboembolism or thrombophilia. We evaluated the usefulness of current and emerging biomarkers for venous thromboembolism, explored the utility of emerging biomarkers for thrombophilia and functionally characterized a novel prothrombotic genetic variant.

Methods: A prospective case-control study of 954 patients with clinically suspected acute deep venous thrombosis or pulmonary embolism were recruited from the emergency department and analyzed by four D-dimer assays, fibrin monomers, thrombin generation and fibrin aggregation assays. The discriminatory accuracy of all assays and of age-adjusted cutoffs for D-dimer was evaluated. From the special coagulation laboratory, we included 369 patients with clinical criteria for thrombophilia testing. Plasma and DNA samples were analyzed by the global hemostatic assays Overall Hemostatic Potential (OHP) and Endogenous Thrombin Potential (ETP) as well as genotyped for several prothrombotic variants. In a separate study, a novel genetic variant with possible prothrombotic effect was characterized by the same assays, prothrombin levels, mRNA expression, and scanning electron microscopy of fibrin clot structure.

Conclusion: Use of age-adjusted cutoffs for D-dimer could lead to a >5% decrease in false positivity rate and in elderly patients this avoidance of unwarranted radiology could even affect as many as 20% of patients with suspected venous thromboembolism. The Overall Hemostatic Potential, Endogenous Thrombin Potential and fibrin monomer assay were not superior to D-dimer for diagnosis of deep venous thrombosis or pulmonary embolism. Global hemostatic assays and extended investigation of prothrombotic genetic variants discretely improved the predictive ability of the classical genetic thrombophilia markers and the proportion of patients with verifiable hypercoagulability. We could also suggest a connection between increased thrombotic risk and a recently discovered synonymous single nucleotide polymorphism.

List of scientific papers

I. Farm M, Siddiqui AJ, Onelöv L, Järnberg I, Eintrei J, Maskovic F, Kallner A, Holmström M, Antovic JP. Age-adjusted D-dimer cut-off leads to more efficient diagnosis of venous thromboembolism in the emergency department: a comparison of four assays. Journal of Thrombosis and Haemostasis. 2018; 16: 866–75.
https://doi.org/10.1111/jth.13994

II. Farm M, Antovic A, Schmidt DE, Bark N, Soutari N, Siddiqui AJ, Holmström M, Pruner I, Antovic JP. Diagnostic accuracy in acute venous thromboembolism: comparing D-dimer, thrombin generation, overall hemostatic potential and fibrin monomers. [Submitted]

III. Farm M, Schmidt DE, Onelöv L, Zong Y, Antovic A, Fahlén A, Soutari N, Bark N, Pruner I, Antovic JP. Thrombin generation and fibrin aggregation in clinically suspected thrombophilia. [Manuscript]

IV. Pruner I, Farm M, Tomic B, Gvozdenov M, Kovac M, Miljic P, Soutari N, Antovic A, Radojkovic D, Antovic JP, Djordjevic V. The silence speaks, but we do not listen: synonymous c.1824C>T gene variant in the last exon of the prothrombin gene as a new prothrombotic risk factor. Clinical Chemistry. 2020, 66, 379-389.
https://doi.org/10.1093/clinchem/hvz015

V. Salas E*, Farm M*, Pich S, Onelöv L, Guillen K, Ortega I, Antovic JP, Soria JM. Predictive Ability of Genetic Risk Scores for Venous Thromboembolism Is Similar in Northern and Southern Europe. [Manuscript]