Evolution of Hemostasis Testing: A Personal Reflection Covering over 40 Years of History.

There is no certainty in change, other than change is certain. As Seminars in Thrombosis and Hemostasis celebrates 50 years of publication, I felt it appropriate to reflect on my own 40-year plus scientific career. My career in the thrombosis and hemostasis field did not start until 1987, but the subsequent 35 years reflected a period of significant change in associated disease diagnostics. I started in the Westmead Hospital "coagulation laboratory" when staff were still performing manual clotting tests, using stopwatches, pipettes, test tubes, and a water bath, which we transported to the hospital outpatient department to run our weekly warfarin clinic. Several hemostasis instruments have come and gone, including the Coag-A-Mate X2, the ACL-300R, the MDA-180, the BCS XP, and several StaR Evolution analyzers. Some instruments remain, including the PFA-100, PFA-200, the AggRAM, the CS-5100, an AcuStar, a Hydrasys gel system, and two ACL-TOP 750s. We still have a water bath, but this is primarily used to defrost frozen samples, and manual clotting tests are only used to teach visiting medical students. We have migrated across several methodologies in the 45-year history of the local laboratory. Laurel gel rockets, used for several assays in the 1980s, were replaced with enzyme-linked immunosorbent assay assays and most assays were eventually placed on automated instruments. Radio-isotopic assays, used in the 1980s, were replaced by an alternate safer method or else abandoned. Test numbers have increased markedly over time. The approximately 31,000 hemostasis assays performed at the Westmead-based laboratory in 1983 had become approximately 200,000 in 2022, a sixfold increase. Some 90,000 prothrombin times and activated partial thromboplastic times are now performed at this laboratory per year. Thrombophilia assays were added to the test repertoires over time, as were the tests to measure several anticoagulant drugs, most recently the direct oral anticoagulants. I hope my personal history, reflecting on the changes in hemostasis testing over my career to date in the field, is found to be of interest to the readership, and I hope they forgive any inaccuracies I have introduced in this reflection of the past.

The Role of the von Willebrand Factor Collagen-Binding Assay (VWF:CB) in the Diagnosis and Treatment of von Willebrand Disease (VWD) and Way Beyond: A Comprehensive 36-Year History.

The von Willebrand factor (VWF) collagen binding (VWF:CB) assay was first reported for use in von Willebrand diagnostics in 1986, by Brown and Bosak. Since then, the VWF:CB has continued to be used to help diagnose von Willebrand disease (VWD) (correctly) and also to help assign the correct subtype, as well as to assist in the monitoring of VWD therapy, especially desmopressin (DDAVP). However, it is important to recognize that the specific value of any VWF:CB is predicated on the use of an optimized VWF:CB, and that not all VWF:CB assays are so optimized. There are some good commercial assays available, but there are also some "not-so-good" commercial assays available, and these may continue to give the VWF:CB "a bad reputation." In addition to VWD diagnosis and management, the VWF:CB found purpose in a variety of other applications, from assessing ADAMTS13 activity, to investigation into acquired von Willebrand syndrome (especially as associated with use of mechanical circulatory support or cardiac assist devices), to assessment of VWF activity in disease states in where an excess of high-molecular-weight VWF may accumulate, and lead to increased (micro)thrombosis risk (e.g., coronavirus disease 2019, thrombotic thrombocytopenic purpura). The VWF:CB turns 37 in 2023. This review is a celebration of the utility of the VWF:CB over this nearly 40-year history.

Epidemiology and Predisposing Factors of Post-COVID Venous Thrombosis: A Concise Review.

Long-coronavirus disease 2019 (COVID-19) represents a heterogeneous clinical syndrome characterized by a pathologic continuum of signs, symptoms, and also laboratory/radiologic abnormalities that may persist for a long time after recovering from an acute severe acute respiratory syndrome-coronavirus disease 2 infection. Among the various components of this postviral condition, the risk of venous thromboembolism in patients hospitalized for COVID-19 remains considerably higher after discharge, especially in older individuals, in men, in patients with longer hospital stays and more aggressive treatment (e.g., mechanical ventilation and/or intensive care), when thromboprophylaxis is not used, and in those with a persistent prothrombotic state. Patients who have these predisposing factors should be monitored more closely to intercept any thrombosis that may occur in a post-COVID time-related manner but may also benefit from extended thromboprophylaxis and/or antiplatelet therapy.

Pearls and Pitfalls in the Measurement of Direct Oral Anticoagulants.

Due to their widespread use, testing for direct oral anticoagulants (DOACs) has become urgent in certain clinical situations. Screening based on widely available, rapid, and simple hemostasis assays such as prothrombin time, activated partial thromboplastin time, or even diluted Russel Viper venom time may provide sufficient evidence of "over-coagulation" and could be used "in small/peripheral/spoke laboratories" as an emergency strategy, but is not thought to be reliable for driving clinical decision making. Given their good correlation with plasma concentration, urine dipsticks may be considered a valuable alternative for emergency screening, although their performance is dependent on renal function, may vary depending on the time since the last urination, and there may be problems of interfacing with the laboratory/hospital information system. Separation methods based on liquid chromatography and mass spectrometry may be clinically questionable, since they measure the concentration rather than the actual inhibitory effect of DOACs, are relatively expensive, cumbersome and time consuming, and therefore seem unsuitable for most conditions requiring urgent clinical decision making. A proposed approach therefore involves establishing a network of routine clinical laboratories, designating a reference center where DOAC tests could be available 24/7, establishing a clear diagnostic care pathway for ordering the tests from the laboratory and standard operating procedures for performing them, the use of the diluted thrombin time for dabigatran and anti-FXa assays (drug-calibrated) for rivaroxaban, apixaban, and edoxaban, as well as providing expert advice throughout the testing process, from ordering to interpretation of results.

Are Antiphospholipid Antibodies a Surrogate Risk Factor for Thrombosis in Sepsis?

Antiphospholipid syndrome (APS) is a hypercoagulable state caused by antiphospholipid antibodies (aPL). APS clinically manifests with arterial or venous or microvascular thrombi and/or pregnancy complications. It is well-known that the development of aPL can be a transient phenomenon and thus the current diagnostic criterion for APS requires repeat laboratory testing several weeks apart before a definitive diagnosis is made. However, transient presence of aPL may also be pathogenic. In this article, we attempt to give historical and clinical evidence for the importance of these antibodies, even when transient, and call for further research into mechanisms by which these antibodies may promote thrombosis and pregnancy morbidities.

Venous Thrombosis in Airborne Viral Infections: Is Coronavirus Disease 2019 now Any Different from Influenza?

One of the hallmarks of coronavirus disease 2019 (COVID-19), particularly in complicated cases (i.e., requiring hospitalization or intensive care support), is persistent hemostasis activation, which may be associated with a vast array of thrombotic episodes involving both the arterial and venous systems. The renewed emphasis on the relationship between viral infections and venous thrombosis paves the way for determining whether a more common and often underestimated infection disease, such as influenza, may also be associated with a significant burden of venous thrombotic episodes, and how this eventual thrombotic risk compares to that seen in COVID-19, both in the past and with newer variants. Our review of studies comparing the burden of venous thromboembolism (VTE) in patients with COVID-19 or influenza revealed that the thrombotic risk appears to be significantly higher in patients with COVID-19 but remains certainly not meaningless in those with influenza, particularly in subjects infected by highly virulent strains (i.e., H1N1), in those who develop pneumonia and require intensive care support. In these specific clinical settings, the adoption of tailored thromboprophylaxis may be indicated though more studies are compellingly needed on this matter. As COVID-19 variants emerge, there is a possibility that the VTE burden of COVID-19 will decrease, and progress to that of other respiratory viruses.

Variable Performance of D-dimer Testing by Hemostasis Laboratories: The Australasian/Asia-Pacific Experience.

D-dimers represent the breakdown products of fibrin. Thus, elevated plasma D-dimers will arise following a thrombotic event, such as a deep vein thrombosis or a pulmonary embolism, and therefore, a nonelevated D-dimer is used to effectively exclude such events. D-dimers are also elevated in a range of other conditions, for example, during disseminated intravascular coagulation. D-dimer levels may also be associated with prognostic value. For example, highly raised D-dimer levels can be associated with worsening clinical features in coronavirus disease 2019. Thus, D-dimer testing represents a commonly requested hemostasis test, often performed in 24/7 laboratories. Unfortunately, D-dimer testing is neither standardized nor harmonized across manufacturers or laboratories. Indeed, considering reporting units and the magnitude of units, up to 28 different combinations may be reported by laboratories. We provide updated findings for D-dimer testing in our geographic region, using recent data from the Royal College of Pathologists of Australasia Quality Assurance Programs, an international external quality assessment program, currently with over 450 participants in the D-dimer module. Data show a wide variety of assays in use and variable outcomes in reported numerical values when assessing proficiency samples. D-dimer testing mostly comprised reagents from three main manufacturing suppliers, with a small number of users of reagents from other manufacturers. Reported results showed important differences in numerical values for the same homogeneous tested samples when normalized to a single reporting unit (e.g., mg/L). Nevertheless, despite using different test reagents and reporting, most participants uniformly identified D-dimer values as below or above a "detection" cut-off for samples that were constructed to be below or above most cut-off values. As expected, mixed findings were reported for samples containing levels around expected cut-off values. We hope that our findings, reflecting on the heterogeneity of test reagents and test data, help improve diagnostic testing for D-dimer testing and facilitate harmonization and standardization, in the future.

Effects of Recombinant SARS-CoV-2 Spike Protein Variants on Platelet Morphology and Activation.

Platelets are central elements of hemostasis and also play a pivotal role in the pathogenesis of thrombosis in coronavirus disease 2019. This study was planned to investigate the effects of different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recombinant spike protein variants on platelet morphology and activation. Citrated whole blood collected from ostensibly healthy subjects was challenged with saline (control sample) and with 2 and 20 ng/mL final concentration of SARS-CoV-2 recombinant spike protein of Ancestral, Alpha, Delta, and Omicron variants. Platelet count was found to be decreased with all SARS-CoV-2 recombinant spike protein variants and concentrations tested, achieving the lowest values with 20 ng/mL Delta recombinant spike protein. The mean platelet volume increased in all samples irrespective of SARS-CoV-2 recombinant spike protein variants and concentrations tested, but especially using Delta and Alpha recombinant spike proteins. The values of both platelet function analyzer-200 collagen-adenosine diphosphate and collagen-epinephrine increased in all samples irrespective of SARS-CoV-2 recombinant spike protein variants and concentrations tested, and thus reflecting platelet exhaustion, and displaying again higher increases with Delta and Alpha recombinant spike proteins. Most samples where SARS-CoV-2 recombinant spike proteins were added were flagged as containing platelet clumps. Morphological analysis revealed the presence of a considerable number of activated platelets, platelet clumps, platelet-monocyte, and platelet-neutrophils aggregates, especially in samples spiked with Alpha and Delta recombinant spike proteins at 20 ng/mL. These results provide support to the evidence that SARS-CoV-2 is capable of activating platelets through its spike protein, though such effect varies depending on different spike protein variants.

EFLM Task Force Preparation of Labs for Emergencies (TF-PLE) recommendations for reinforcing cyber-security and managing cyber-attacks in medical laboratories.

The healthcare systems are a prime target for cyber-attacks due to the sensitive nature of the information combined with the essential need for continuity of care. Medical laboratories are particularly vulnerable to cyber-attacks for a number of reasons, including the high level of information technology (IT), computerization and digitization. Based on reliable and widespread evidence that medical laboratories may be inadequately prepared for cyber-terrorism, a panel of experts of the Task Force Preparation of Labs for Emergencies (TF-PLE) of the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) has recognized the need to provide some general guidance that could help medical laboratories to be less vulnerable and better prepared for the dramatic circumstance of a disruptive cyber-attack, issuing a number of consensus recommendations, which are summarized and described in this opinion paper.

What We Know (and Do not Know) Regarding the Pathogenesis of Pulmonary Thrombosis in COVID-19.

The clinical course of coronavirus disease 2019 (COVID-19) is often complicated by the onset of venous thrombosis and thromboembolism (VTE), encompassing also pulmonary thrombosis. Recent statistics attests that the cumulative frequency of VTE can be as high as 30% in COVID-19 hospitalized patients, increasing to nearly 40 to 70% (depending on systematic screening) in those with severe illness, mechanical ventilation, or intensive care unit admission. The risk of venous thrombosis seems mostly limited to the active phase of disease, and is directly associated with some genetic (i.e., inherited prothrombotic predisposition) and demographical factors (male sex, overweight/obesity), disease severity (risk increasing progressively from hospitalization to development of severe illness, being the highest in patients needing mechanical ventilation and/or intensive care), presence and extent of pulmonary disease, coexistence of multiple risk factors (immobilization, mechanical ventilation, co- or superinfections), along with increased values of inflammatory and thrombotic biomarkers. At least three different phenotypes of pulmonary thrombosis may develop in COVID-19 patients, one caused by typical embolization from peripheral venous thrombosis (e.g., deep vein thrombosis), a second type triggered by local inflammation of nearby pulmonary tissue, and a third one mostly attributable to the prothrombotic state consequent to the pronounced systemic inflammatory response (i.e., the so-called cytokine storm) that is frequently observed in COVID-19. Although the pathogenesis of these three conditions has different features, their discrimination is essential for diagnostic and therapeutic purposes. The prognosis of COVID-19 patients who develop pulmonary thrombosis is also considerably worse than those who do not, thus probably needing frequent monitoring and more aggressive therapeutic management.

Variable Performance of Lupus Anticoagulant Testing: The Australasian/Asia-Pacific Experience.

Lupus anticoagulant (LA) is one of three tests identified as laboratory criteria for definite antiphospholipid syndrome (APS). The other two tests are anticardiolipin antibody (aCL) and anti-ß2-glycoprotein I (aß2GPI) antibody. The presence of LA is assessed using clot-based tests, while the presence of aCL and aß2GPI is assessed by immunological assays. Since no test can be considered 100% sensitive or specific for LA, current guidelines recommend using two different clot-based assays reflecting different principles, with the dilute Russell viper venom time (dRVVT) and activated partial thromboplastin time (aPTT) recommended. Initially, LA-sensitive reagents are used to screen for LA, and then, in "screen-positive" samples, LA-"insensitive" reagents are used to confirm LA. Because LA assays are based on clot detection, anything that can interfere with fibrin clot development may affect test results. In particular, in addition to LA, the tests are also sensitive to the presence of a wide range of clinical anticoagulants, reflecting preanalytical issues for testing. We provide updated findings for LA testing in our geographic region, using recent data from the Royal College of Pathologists of Australasia Quality Assurance Programs, an international external quality assessment program with approximately 120 participants. Data show a wide variety of assays in use, especially for aPTT testing, and variable outcomes in reported numerical values with these assays when assessing proficiency samples. dRVVT testing mostly comprised reagents from three main manufacturing suppliers, which also showed differences in numerical values for the same homogeneous tested samples. Nevertheless, despite the use of different test reagents and processes, >98% of participants correctly identified LA-negative samples as LA-negative and LA-positive samples as LA positive. We hope our findings, reflecting on the heterogeneity of test processes and test data, help improve diagnostic testing for LA in the future.

Mechanisms of Thrombosis in Heparin-Induced Thrombocytopenia and Vaccine-Induced Immune Thrombotic Thrombocytopenia.

Heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombotic thrombocytopenia (VITT) are rare, iatrogenic immune-mediated conditions with high rates of thrombosis-related morbidity and mortality. HIT is a long-recognized reaction to the administration of the common parenterally administered anticoagulant heparin (or its derivatives), while VITT is a new, distinct syndrome occurring in response to adenovirus-based vaccines against coronavirus disease 2019 and potentially other types of vaccines. A feature of both HIT and VITT is paradoxical thrombosis despite a characteristic low platelet count, mediated by the presence of platelet-activating antibodies to platelet factor 4. Several additional factors have also been suggested to contribute to clot formation in HIT and/or VITT, including monocytes, tissue factor, microparticles, endothelium, the formation of neutrophil extracellular traps, complement, procoagulant platelets, and vaccine components. In this review, we discuss the literature to date regarding mechanisms contributing to thrombosis in both HIT and VITT and explore the pathophysiological similarities and differences between the two conditions.

D-dimer: old dogmas, new (COVID-19) tricks.

D-dimer is a fibrin degradation product encompassing multiple cross-linked D domains and/or E domains present in the original fibrinogen molecule, whose generation is only theoretically possible when hemostasis and fibrinolysis pathways are concomitantly activated. D-dimer measurement has now become a pillar in the diagnosis/exclusion and prognostication of venous thromboembolism (VTE) and disseminated intravascular coagulation (DIC), when incorporated into validated clinical algorithms and especially using age-adjusted diagnostic thresholds. Although emerging evidence is also supporting its use for predicting the duration of anticoagulant therapy in certain categories of patients, the spectrum of clinical applications is constantly expanding beyond traditional thrombotic pathologies to the diagnosis of acute aortic dissection, acute intestinal ischemia and cerebral venous thrombosis among others, embracing also clinical management of coronavirus disease 2019 (COVID-19). Recent findings attest that D-dimer elevations are commonplace in patients with severe acute respiratory syndrome (SARS-CoV-2) infection (especially in those with thrombosis), its value predicts the clinical severity (up to death) of COVID-19 and remains more frequently increased in COVID-19 patients with post-discharge clinical sequelae. Further, D-dimer-based anticoagulant escalation may be associated with a lower risk of death in patients with severe SARS-CoV-2 infection and, finally, D-dimer elevation post-COVID-19 vaccination mirrors an increased risk of developing vaccine-induced thrombocytopenia and thrombosis (VITT).

Towards 50 years of platelet function analyser (PFA) testing.

The platelet function analyser (PFA) is a prevalent platelet function screening instrument, and comes in two models-the original PFA-100 and the contemporary PFA-200. The instruments have 'identical' output, being a 'closure time' (CT). Moreover, normal reference ranges provided by the manufacturer, for the specific test cartridges, are the same for both models. There are three different types of test cartridge: collagen/epinephrine (C/Epi), collagen/adenosine diphosphate (C/ADP), and "Innovance PFA P2Y" (only available in certain geographical locations). The PFA-100 was released in the mid 1990s, and so is approaching 50 years of age. The PFA-200, released in some locations in the mid 2010s, is destined to eventually replace the PFA-100, but is not yet available in the USA. The test system is highly sensitive to von Willebrand disease (VWD; C/Epi and C/ADP) and to aspirin therapy (C/Epi only), but only has moderate sensitivity to defects in platelet function and/or deficiencies in platelet number. Accordingly, recommendations for use for screening platelet function vary according to user experience. Some workers have alternatively used the PFA to assess thrombosis risk or pre-operative bleeding risk. In this review, we provide an overview of the history of PFA, and summarise its current clinical utility.

Cerebral Venous Thrombosis Developing after COVID-19 Vaccination: VITT, VATT, TTS, and More.

Despite the huge efforts globally underway for preventing or limiting the spread of severe acute respiratory coronavirus disease 2 (SARS-CoV-2), the coronavirus disease 2019 (COVID-19) pandemic outbreak appears still virtually unstoppable. As for many other infectious diseases, COVID-19 vaccination has now become crucial for limiting viral spread, especially for averting hospitalizations, need for intensive care, and fatal outcome. Nonetheless, as for other vaccines, COVID-19 vaccination is not completely free from side effects. Among the adverse events that have been reported after receiving COVID-19 vaccination, special emphasis has been given to an unexpected number of thrombocytopenic episodes with or without thrombotic complications, especially in recipients of adenovirus-based COVID-19 vaccines. Along with a specific clinical presentation, encompassing "atypical" thrombosis (especially cerebral venous [sinus] thrombosis, CVT) more prevalent in young female subjects, this new syndrome called vaccine-induced thrombocytopenia and thrombosis (VITT) is characterized by, and thereby diagnosed for, the presence of three paradigmatic laboratory abnormalities, i.e., low platelet count (<150 × 109/L), elevated plasma D-dimer levels (>0.5 mg/L), accompanied by a positive test for anti-PF4 (platelet factor 4) antibodies assayed with ELISA (enzyme-linked immunosorbent assay) techniques. Timely identification of these important abnormalities by both clinicians and laboratory professional is essential for early diagnosis and management of VITT, since the outcome of this condition may be fatal in half or even more of effected patients with severe disease. Therefore, this narrative review aims to review here the epidemiology, pathogenesis, clinical, and laboratory characteristics of VITT and other COVID-19 vaccine-associated thrombocytopenias.

Laboratory Diagnosis of von Willebrand Disease (VWD): Geographical Perspectives.

von Willebrand disease (VWD) is reportedly the most common inherited bleeding disorder, and can also arise as an acquired (von Willebrand) syndrome (AVWS). The hemostasis laboratory plays a key role in the diagnosis or exclusion of VWD/AVWS, which may otherwise be suspected due to the patient's clinical (bleeding) history. VWD/AVWS arise from deficiency and/or defects in the adhesive plasma protein, von Willebrand factor (VWF). VWF undertakes various roles within hemostasis, but principally acts within primary hemostasis to anchor platelets to sites of vascular damage, thereby facilitating thrombus formation to arrest bleeding. The diagnosis or exclusion of VWD/AVWS requires laboratory testing for both VWF level and activity, with the latter potentially comprising several of a potential plethora of different assays. Complete diagnosis of VWD also requires the differentiation of VWD type, with six types comprising the current classification (i.e., qualitative [types 2A, 2B, 2M, 2N VWD] vs. quantitative [types 1 and 3 VWD] deficiency/defects). Although appropriate diagnosis and type classification hold important therapeutic consequences, these remain problematic and sometimes elusive for some laboratories to achieve. This report reviews the laboratory aided diagnosis or exclusion of VWD from a geographic perspective, and focuses on the disparities of approaches and methods in different regions of the world. This is primarily done from the perspective of data available from published reports related to external quality assessment (or proficiency testing) from different geographic localities. Moreover, differences in approaches between laboratories may arise due to differential adherence of particular guidelines, as well as regulatory aspects and predominance of local manufacturers and suppliers.

Evaluating Performance of Contemporary and Historical von Willebrand Factor (VWF) Assays in the Laboratory Identification of von Willebrand Disease (VWD): The Australasian Experience.

von Willebrand disease (VWD) is a common bleeding disorder that arises from deficiency and/or defects of von Willebrand factor (VWF). Appropriate diagnosis of VWD, including differential identification of qualitative (types 2A, 2B, 2M, 2N VWD) versus quantitative (types 1 and 3 VWD) defects remains problematic but has important management implications, given differential therapy. Complete assessment for VWD in a patient with a bleeding history requires comprehensive test panels, including VWF activity and antigen. We describe the Australasian experience, using data from the Royal College of Pathologists of Australasia (RCPA) Quality Assurance Program (QAP) related to VWF testing in their VWD test module. The RCPAQAP has been providing samples for VWF testing since 1998, representing 25 years of proficiency testing related to VWD diagnosis. A total of 109 samples have been dispatched to participants over these years, with current assessment involving dispatches of two samples (=4 samples) per year. Samples have represented all types of VWD, as well as normal or other samples, including acquired von Willebrand syndrome and plasma VWF concentrates as used in VWD therapy. Different VWF assays and activity/antigen ratios show different utility in VWD and type identification. In the past 9 years of data capture, a total of 166 errors were identified from a total of 1,839 interpretations, representing a base error rate of 9.0%. Identification errors were highest for type 2 VWD samples (15.3%), intermediate for type 1 VWD samples (7.5%), and lowest for normal samples (2.4%). Errors can be linked to assay limitations, including assay variability and low-level VWF detection limits, as well as laboratory issues (including test result misinterpretation, which accounts for approximately 40% of all errors for type 2 VWD). For test-associated errors, VWF:RCo and VWF:GPIbM were associated with the highest variability and error rate, which was up to 10x higher than that using VWF:CB. As a test group, chemiluminescence-based procedures were associated with lowest inter-laboratory variability, best low-level VWF detection (down to <1 U/dL), and least errors overall. These findings inform on reasons behind high rates of errors associated with VWD diagnosis, with some assays and methodologies performing substantially better than others.

D-dimers-"Normal" Levels versus Elevated Levels Due to a Range of Conditions, Including "D-dimeritis," Inflammation, Thromboembolism, Disseminated Intravascular Coagulation, and COVID-19.

D-dimers reflect a breakdown product of fibrin. The current narrative review outlines how D-dimers can arise in normal individuals, as well as in patients suffering from a wide range of disease states. D-dimers in normal individuals without evident thrombosis can arise from background fibrinolytic activity in various tissues, including kidney, mammary and salivary glands, which ensures smooth flow of arising fluids where any blood contamination could be immediately lysed. In addition, healthy individuals can also regularly sustain minor injuries, often unbeknown to them, and wound healing follows clot formation in these situations. D-dimers can also arise in anxiety and following exercise, and are also markers of inflammation. Lung inflammation (triggered by microbes or foreign particles) is perhaps also particularly relevant, since the hemostasis system and fibrinolysis help to trap and remove such debris. Lung inflammation in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may contribute to D-dimer levels additive to thrombosis in patients with COVID-19 (coronavirus disease 2019). Indeed, severe COVID-19 can lead to multiple activation events, including inflammation, primary and secondary hemostasis, and fibrinolysis, all of which may contribute to cumulative D-dimer development. Finally, D-dimer testing has also found a role in the diagnosis and triaging of the so-called (COVID-19) vaccine-induced thrombotic thrombocytopenia.

COVID-19 and Antiphospholipid Antibodies: Time for a Reality Check?

Antiphospholipid antibodies (aPL) comprise a panel of autoantibodies that reflect a potential prothrombotic risk in several autoimmune conditions, most notably antiphospholipid (antibody) syndrome (APS). aPL can be divided into those that form part of the laboratory criteria for APS, namely, lupus anticoagulant (LA), as well as anticardiolipin antibodies (aCL) and anti-ß2-glycoprotein I antibodies (aß2GPI) of the immunoglobulin G and M classes, and those that form a group considered as "noncriteria antibodies." The noncriteria antibodies include, for example, antiphosphatidylserine antibodies (aPS), antiprothrombin antibodies (aPT), and antiphosphatidylserine/prothrombin complex antibodies (aPS/PT). COVID-19 (coronavirus disease 2019) represents a prothrombotic disorder, and there have been several reports of various aPL being present in COVID-19 patients. There have also been similarities drawn between some of the pathophysiological features of COVID-19 and APS, in particular, the most severe form, catastrophic APS (CAPS). In this review, we critically appraise the literature on aPL and COVID-19. This is a companion piece to a separate review focused on LA. In the current review, we primarily concentrate on the so-called solid phase identifiable aPL, such as aCL and aß2GPI, but also reflect on noncriteria aPL. We conclude that aPL positivity may be a feature of COVID-19, at least in some patients, but in general, identified "solid-phase" aPL are of low titer and not able to be well-linked to the thrombotic aspects of COVID-19. Also, most publications did not assess for aPL persistence, and where persistence was checked, the findings appeared to represent transient aPL. Importantly, high-titer aPL or multiple aPL positivity (including double, triple) were in the minority of COVID-19 presentations, and thus discount any widespread presence of APS, including the most severe form CAPS, in COVID-19 patients.

Is Lupus Anticoagulant a Significant Feature of COVID-19? A Critical Appraisal of the Literature.

The term "lupus anticoagulant (LA)" identifies a form of antiphospholipid antibodies (aPLs) causing prolongation of clotting tests in a phospholipid concentration-dependent manner. LA is one of the laboratory criteria identified in patients with antiphospholipid (antibody) syndrome (APS). The presence of LA in patients with APS represents a significant risk factor for both thrombosis and pregnancy morbidity. There have been several reports of similarities between some of the pathophysiological features of COVID-19 and APS, in particular the most severe form, catastrophic APS. There have also been many reports identifying various aPLs, including LA, in COVID-19 patients. Accordingly, a very pertinent question arises: "Is LA a feature of COVID-19 pathology?" In this review, we critically appraise the literature to help answer this question. We conclude that LA positivity is a feature of COVID-19, at least in some patients, and potentially those who are the sickest or have the most severe infection. However, many publications have failed to appropriately consider the many confounders to LA identification, being assessed using clot-based assays such as the dilute Russell viper venom time, the activated partial thromboplastin time (aPTT), and the silica clotting time. First, most patients hospitalized with COVID-19 are placed on anticoagulant therapy, and those with prior histories of thrombosis would possibly present to hospital already on anticoagulant therapy. All anticoagulants, including vitamin K antagonists, heparin (both unfractionated heparin and low-molecular-weight heparin), and direct oral anticoagulants affect these clot-based assays. Second, C-reactive protein (CRP) is highly elevated in COVID-19 patients, and also associated with severity. CRP can also lead to false-positive LA, particularly with the aPTT assay. Third, persistence of aPL positivity (including LA) is required to identify APS. Fourth, those at greatest risk of thrombosis due to aPL are those with highest titers or multiple positivity. Most publications either did not identify anticoagulation and/or CRP in their COVID-19 cohorts or did not seem to account for these as possible confounders for LA detection. Most publications did not assess for aPL persistence, and where persistence was checked, LA appeared to represent transient aPL. Finally, high titer aPL or multiple aPL positivity were in the minority of COVID-19 presentations. Thus, at least some of the reported LAs associated with COVID-19 are likely to be false positives, and the relationship between the detected aPL/LA and COVID-19-associated coagulopathy remains to be resolved using larger and better studies.