Leonardo Pasalic

Treatment of von Willebrand Disease

Congenital von Willebrand disease (VWD) and acquired von Willebrand syndrome (AVWS) reflect conditions caused by von Willebrand factor (VWF) deficiency and/or defects. VWD is the most common inherited bleeding disorder and AVWS arises from a variety of causes. Since VWF stabilizes and protects factor VIII (FVIII) in the circulation, this is also reduced in many patients with VWD. The treatment of VWD and AVWS therefore primarily entails replacement of VWF, and sometimes FVIII, to protect against bleeding. This may entail the use of VWF concentrates (currently plasma-derived) and/or FVIII concentrates (currently plasma-derived or more increasingly recombinant forms), and/or desmopressin to release endogenous VWF in subgroups of patients. For AVWS additional treatment of the underlying condition is also required. Adjunct therapies include antifibrinolytics. Globally, various formulations exist for both VWF and FVIII concentrates and are differentially available based on manufacturer marketing or regulatory approvals/clearances in different geographies. Also, guidelines for treatment of VWD vary for different localities and recombinant VWF is undergoing clinical trials. The current review provides an overview of the treatment of VWD as currently practiced in developed countries, and also provides a glimpse towards the future.

The effect of dabigatran on haemostasis tests: a comprehensive assessment using in vitro and ex vivo samples

Summary The new direct oral anticoagulants (DOACS) dabigatran, rivaroxaban, apixaban and edoxaban provide alternatives to warfarin for treatment and prevention of atrial fibrillation and venous thromboembolic disease in various settings. These have been developed as not requiring laboratory monitoring; however, under certain clinical situations, including recent haemorrhage/thrombosis, emergency surgical procedures, testing may be indicated. The aim of this study was to assess findings of haemostasis laboratory tests for one of the DOACs, dabigatran (Pradaxa), tested across a wide range of laboratory assays. Laboratories (n = 72) enrolled in the Royal College of Pathologists of Australasia Quality Assurance Programs (RCPAQAP) Haematology program were sent set(s) of seven dabigatran spiked plasma samples covering the concentration 0–800 ng/mL. Also, 30 ex vivo patient samples under therapy with dabigatran were assessed. Prothrombin time and activated partial thromboplastin time assays showed some sensitivity to dabigatran; however, a normal result could not inform on drug exclusion. The thrombin time (TT) was very sensitive to dabigatran, and a normal TT could generally be used for drug exclusion. More specialised assays such as the Hemoclot, a direct thrombin inhibition assay, and in-house dilute TT methods, showed good reproducibility and concordance with expected drug levels assessed by mass spectrometry and were effective to quantify drug levels. Dabigatran also affected factor assays, lupus anticoagulant and factor inhibitor measurement, leading to potential misinterpretation of test results. Ex vivo sample testing provided similar and extended information. Dabigatran affects many haemostasis tests. Some can be used to predict the presence, absence or quantity of dabigatran in patient plasma. For others, interference may lead to false conclusions regarding patients’ haemostatic status.

Necrotic platelets provide a procoagulant surface during thrombosis

A subpopulation of platelets fulfills a procoagulant role in hemostasis and thrombosis by enabling the thrombin burst required for fibrin formation and clot stability at the site of vascular injury. Excess procoagulant activity is linked with pathological thrombosis. The identity of the procoagulant platelet has been elusive. The cell death marker 4-[N-(S-glutathionylacetyl)amino]phenylarsonous acid (GSAO) rapidly enters a subpopulation of agonist-stimulated platelets via an organic anion-transporting polypeptide and is retained in the cytosol through covalent reaction with protein dithiols. Labeling with GSAO, together with exposure of P-selectin, distinguishes necrotic from apoptotic platelets and correlates with procoagulant potential. GSAO(+) platelets form in occluding murine thrombi after ferric chloride injury and are attenuated with megakaryocyte-directed deletion of the cyclophilin D gene. These platelets form a procoagulant surface, supporting fibrin formation, and reduction in GSAO(+) platelets is associated with reduction in platelet thrombus size and fibrin formation. Analysis of platelets from human subjects receiving aspirin therapy indicates that these procoagulant platelets form despite aspirin therapy, but are attenuated by inhibition of the necrosis pathway. These findings indicate that the major subpopulation of platelets involved in fibrin formation are formed via regulated necrosis involving cyclophilin D, and that they may be targeted independent of platelet activation.

Detection of mild inherited disorders of blood coagulation: current options and personal recommendations

Although assessment of prior personal and familial bleeding history is an important aspect of the diagnosis of bleeding disorders, patients with mild inherited bleeding disorders are sometimes clinically asymptomatic until presented with a hemostatic challenge. However, bleeding may occur after incursion of trauma or surgery, so detection of these conditions reflects an important facet of clinical and laboratory practice. Mild bleeding disorders may be detected as a result of family studies or following identification of abnormal values in first-line screening tests such as activated partial thromboplastin time, prothrombin time, fibrinogen and global platelet function screen testing, such as the platelet function analyzer. Following determination of abnormal screening tests, subsequent investigation should follow a systematic approach that targets specific diagnostic tests, and including factor assays, full platelet function assays and more extensive specialized hemostasis testing. The current report provides a personal overview on inherited disorders of blood coagulation and their detection.

Enumeration of extracellular vesicles by a new improved flow cytometric method is comparable to fluorescence mode nanoparticle tracking analysis

UNLABELLED Extracellular vesicles (EVs) play a role in a variety of physiological and pathological processes. However, use of EVs as biomarkers has been hampered by limitations of current detection and enumeration methods. We compared fluorescence-threshold flow cytometry (FT-FC) to nanoparticle tracking analysis (NTA) for enumeration of cell culture-derived EVs. FT-FC and NTA utilising fluorescence mode (F-NTA) enumerated similar numbers of EVs stained with a membrane dye PKH67. Both methods were sufficiently sensitive to detect cell-derived EVs above the background of culture medium. Light scatter NTA (LS-NTA) detected 10-100× more particles than either fluorescence-based method but demonstrated poor specificity. F-NTA appeared to have better sensitivity for <100nm vesicles, however, the FT-FC method combined direct enumeration of EVs with high sensitivity and specificity in the >100nm range. Due to wider availability and higher degree of automation and standardisation, FT-FC is a reasonable surrogate to F-NTA for quantification of EVs. FROM THE CLINICAL EDITOR Extracellular vesicles are small particles, which can act as tools for intercellular communication. One recent area of interest in EVs is their potentials as biomarkers. In this article, the authors investigated and compared fluorescence-threshold flow cytometry (FT-FC) to nanoparticle tracking analysis (NTA) for the detection of EVs and showed that FT- FC method could be more advantageous. This technique should provide a new alternative for the future.

Monitoring Therapy during Treatment of von Willebrand Disease

&NA; von Willebrand factor (VWF) is an adhesive plasma protein that primarily acts to bridge platelets to sites of vascular injury and thus prevent bleeding. von Willebrand disease (VWD) is the most common inherited bleeding disorder and is caused by deficiency and/or defects of VWF, leading to low levels of plasma VWF or dysfunctional VWF. Factor VIII (FVIII) is also reduced in many patients with VWD, since VWF stabilizes and protects FVIII from degradation. Treatment of VWD primarily entails replacement of VWF, and sometimes FVIII, to protect against bleeding. This may entail use of VWF/FVIII concentrates, and/or desmopressin (1‐deamino‐8‐D‐arginine vasopressin) to release endogenous VWF in some patients. Adjunct therapies include antifibrinolytics and hormonal therapies in women. Optimal treatment of VWD entails measuring the effects of treatment, either as a trial before surgery or during therapeutic management. This is usually accomplished by performance of the same tests that are used to help diagnose VWD, although additional monitoring (clinically and/or by laboratory testing) may also be performed. The current review provides an overview of the treatment of VWD but is primarily focused on the monitoring of such therapy.

Clinical and laboratory diagnosis of heparin induced thrombocytopenia: an update

Heparin remains a commonly used anticoagulant in prophylaxis and treatment of venous and arterial thrombosis, in addition to ensuring patency of artificial blood circuits such as cardiopulmonary bypass (CPB). Heparin induced thrombocytopenia (HIT) is a rare but potentially fatal complication of heparin therapy that results from production of polyclonal antibodies to heparin in complex, usually with platelet factor 4 (PF4). In a proportion of patients, this causes platelet activation and thrombin generation, which may result in thrombosis. However, identification of patients with HIT can be complicated as thrombocytopenia is common in hospitalised patients receiving heparin, and is usually due to other causes. Clinical assessment of the likelihood of HIT is paramount in order to make appropriate decisions regarding laboratory investigations and ongoing anticoagulation, especially given clinically expressed pro-thrombotic states. However, clinical assessment, on its own, cannot guarantee diagnosis or exclusion of HIT, and therefore is facilitated by laboratory testing, although unfortunately, this is frequently limited by local availability of assays and delay in availability of results. Nevertheless, there are an increasing number of available laboratory tests that can be used to identify antibodies causing HIT, including both immunological and functional assays. This narrative review will discuss the existing tools for clinical assessment in addition to evaluating the advantages and disadvantages of the available laboratory assays for HIT.

Therapeutic monitoring of unfractionated heparin – trials and tribulations

ABSTRACT Introduction: Heparin is one of the oldest biological medicines with an established role in prevention and treatment of arterial and venous thromboembolism. Published therapeutic ranges for unfractionated heparin (UFH) mostly precede the large increase in the number of activated partial thromboplastin time (APTT) reagent/instrument combinations that now show wide variability. Areas covered: This paper explores the use of UFH, the development of heparin therapeutic ranges (HTRs), and the strengths and limitations of the methods used to monitor heparin’s anticoagulant effect. Expert commentary: Despite longstanding use of UFH for management of thromboembolic conditions, the optimal test for monitoring UFH remains undetermined. Although used extensively for monitoring UFH, routine APTT-derived HTRs are based on limited science that may have little relevance to current laboratory practice. Anti-FXa levels may provide better and more reliable HTRs; however, even these levels show considerable inter-laboratory variation, and there are insufficient clinical studies proving improved clinical efficacy. Alternative tests for monitoring UFH reported over time have not been proven effective nor feasible, secondary to technical or cost issues, or lack of general adoption. Thus, despite limited evidence of clinical utility, an uncomfortable marriage of convenience represented by heparin laboratory monitoring is unlikely to be terminated in the immediate future.

Platelets as Biomarkers of Coronary Artery Disease

Primary and secondary prevention of cardiovascular disease remain a public health priority. Effective risk stratification of patients is a central requisite for effective preventative care and several scoring systems incorporating biomarkers have been used for prognostication in patients to guide intervention decisions. Thrombosis of atherosclerotic coronary arteries is the main mechanism behind the acute coronary syndromes and since platelets play a pivotal role in the pathogenesis of thrombosis, atherogenesis, and angiogenesis, platelet-derived biomarkers are an attractive concept. This review assesses the potential and the limitations of a range of platelet-based assays as biomarkers for coronary artery disease.

Novel (Oral) Anticoagulant Challenges in Surgery

Summary Non‐vitamin K oral anticoagulants (NOACs) are a relatively recent therapeutic modality for the prevention of systemic thromboembolic complications of atrial fibrillation and the prevention and management of venous thromboembolic disease. Approved indications for this class of anticoagulants are likely to further expand as the results of ongoing and new clinical trials are published and clinical experience grows. Despite their convenience compared with traditional methods of anticoagulation, there remain a few potential pitfalls associated with their use in the perioperative setting. In particular, there is limited experience and evidence base regarding anticoagulant management in the perioperative setting, especially given the different NOACs available, which in turn are different from the classical anticoagulants. This narrative review synthesizes the recent advances in development of specific NOAC reversal agents and the understanding of the complexities of laboratory measurement of NOAC anticoagulant effects, and aims to provide practicing clinicians with basic evidence‐based tools for perioperative management of patients taking NOACs.