Laboratory testing for lupus anticoagulant (LA) in patients taking direct oral anticoagulants (DOACs): potential for false positives and false negatives

New method to differentiate between lupus anticoagulants, progressive coagulation inhibitors and coagulation factor deficiencies in the mixing tests

INTRODUCTION

Mixing tests in activated partial thromboplastin time (APTT) are used for the differentiation between lupus anticoagulants (LA), coagulation inhibitors, and factor deficient samples with APTT prolongation. However, the indexes for the differentiation have not been established. The present study aimed to develop new mixing test indexes for the differentiation.

METHODS

Twenty-six LA-positive, 8 progressive coagulation factor VIII inhibitor, and 35 coagulation deficient samples were employed. APTT were measured for normal plasma, patient plasma, and mixing plasma prepared at a ratio of 1:1 proportion in both without incubation and 2 h-incubation. New two parameters named as ALD50 and mixture plasma-patient plasma after Warming change rate Subtraction (WaS) calculated from the clotting times of normal, 1:1 mixing and patient samples with/without 2 h-incubation were established. In the samples with WaS result of <10.2%, ALD50 of ≥87.8%, and < 87.8% were defined as LA and coagulation factor deficiency, respectively, and WaS of ≥10.2% defined progressive coagulation factor inhibitors.

RESULTS

Sensitivity and specificity to LA were 80.8% and 93.0% for ALD50, and sensitivity and specificity to progressive coagulation factor inhibitor were 100.0% and 100.0% for WaS, respectively. The agreement between sample classification and WaS-ALD50 was 88.4% (61/69).

CONCLUSIONS

ALD50 and WaS showed acceptable sensitivity and specificity to LA and progressive coagulation factor inhibitor, respectively. These indexes would be useful for the differentiation between LA, factor deficiency, and progressive coagulation factor inhibitor in the mixing tests.

Testing for the lupus anticoagulant: the good, the bad, and the ugly

Lupus anticoagulant (LA) represents 1 of the laboratory criteria for classification of patients as having definite antiphospholipid syndrome (APS). The other 2 laboratory criteria are anticardiolipin antibodies and anti-beta2-glycoprotein I antibodies. At least 1 of these antiphospholipid antibody (aPL) tests need to be positive, with evidence of persistence, together with evidence of at least 1 clinical criterion for APS, before a patient can be classified as having definite APS. LA and other aPL assays are also important for diagnosis or exclusion of APS, as well as for risk stratification, with triple-positive patients carrying the greatest risk. Whereas LA is identified through "uncalibrated" clot-based assays, the other aPL assays (anticardiolipin and anti-beta2-glycoprotein I antibodies) represent immunological assays, identified using calibrated solid-phase methods. Because LA is identified using clot-based assays, it is subject to considerable preanalytical and analytical issues that challenge accurate detection or exclusion of LA. In this narrative review, we take a look at the good, the bad, and the ugly of LA testing, primarily focusing on the last 10 years. Although harmonization of LA testing as a result of International Society on Thrombosis and Haemostasis guidance documents and other international activities has led to improvements in LA detection, many challenges remain. In particular, several anticoagulants, especially direct oral anticoagulants and also vitamin K antagonists, given as therapy to treat the pathophysiological consequences of aPL, especially thrombosis, interfere with LA assays and can generate false-positive or false-negative LA findings. Overcoming these diagnostic errors will require a multifaceted approach with clinicians and laboratories working together.

A comparative in vitro study of the anticoagulant effect of branded versus generic rivaroxaban

BACKGROUND

Several generic formulations of rivaroxaban were recently marketed to be used interchangeably with their branded equivalent. However, there have been no previously published studies that directly compared the in vitro anticoagulant effect of branded vs. generic rivaroxaban. The aim of this in vitro study was to compare the effects of three raw rivaroxaban materials, obtained from the branded (Xarelto®) and two generic (Rivarolto® and Rivaroxaban Sandoz®) rivaroxaban formulations on an array of coagulation assays.

METHODS

A pool of normal plasma was spiked with several concentrations of the three rivaroxaban (range 50-750 ng/ml). The concentrations were assessed with a rivaroxaban calibrated anti-Xa assay and confirmed by ultra-high-performance liquid chromatography-mass spectrometry coupled with tandem mass spectrometry (UHPLC-MS/MS). The following assays were performed: Prothrombin time (PT), activated Partial Thromboplastin time (aPTT), Diluted Russell's Viper Venom Test (dRVVT), Thrombin time (TT), Clauss Fibrinogen, Factor VII, VIII and IX assays, and thromboelastography.

RESULTS

The results obtained by the three rivaroxaban at similar concentrations were comparable. Increasing concentrations of the three rivaroxaban showed a strong positive correlation with the PT, aPTT and dRVVT assays (r > 0.95, p < 0.01 for all), and a strong negative correlation with the Factors assays (r < -0.95, p < 0.01 for all). TT and Clauss Fibrinogen were not affected by rivaroxaban. No significant difference was identified in the mean assays' results obtained by the three rivaroxaban.

CONCLUSION

This study showed that the branded and generic rivaroxaban exert an identical in vitro anticoagulant effect across a wide range of concentrations.

Viewpoint: Lupus anticoagulant detection and interpretation in antiphospholipid syndrome

Lupus anticoagulant (LA) is a well-established risk factor for the clinical manifestations of antiphospholipid syndrome (APS). Accurate LA detection is an essential prerequisite for optimal diagnosis and management of patients with APS or aPL carriers. Variability remains a challenge in LA testing, with reliable detection influenced by multiple factors, including pre-analytical conditions, anticoagulation treatment, choice of tests and procedures performed, as well as interpretation of results, that can lead to false-positives or negatives. A standardised approach to LA testing, following current guidance, based on published data and international consensus, and with attention to detail, is required to underpin accurate detection of LA. Future work should focus on better characterisation of the nature of LA, which may ultimately lead to improved diagnosis and management of patients with APS and aPL carriers. This article reviews current practice and challenges, providing an overview on detection of LA.

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.

Thrombin generation assay and lupus anticoagulant synergically distinguish populations of patients with antiphospholipid antibodies

AIM

To apply thrombin generation assay (TGA) in a large cohort of antiphospholipid antibodies (aPL)-positive patients.

MATERIAL AND METHODS

108 patients were tested with TGA and lupus anticoagulant (LA) testing and divided according to their aPL profile. Briefly, 21 patients were positive for anti-phosphatidylserine (aPS)/prothrombin (PT) IgG/IgM (group1), 29 for anti-ß2-glycoprotein-I (aβ2GPI) and anti-cardiolipin (aCL) IgG/IgM (group2), 31 for aPS/PT, aβ2GPI and aCL IgG/IgM (group3), 27 for aPS/PT and/or aβ2GPI+aCL IgM at low-titres (group4). 31 healthy donors (HDs) and 24 controls treated with vitamin K antagonists (VKA) were included.

RESULTS

The most deranged TGA and LA profiles were observed in tetra-positive patients (group3) that differed significantly to the other groups, thus those with isolated, double or triple aPL-positivity. Moreover, when comparing the TGA profile of all antiphospholipid syndrome (APS) patients, aPL-carriers, HDs and VKA controls, we observed that the aPL+ patients (especially APS) showed a distinctive profile that allowed to distinguish them from the other groups with significantly higher tLag and tPeak, and lower Peak and area under the curve.When focusing on APS clinical manifestations, patients with a high-risk profile (group3) showed significant differences from those presenting low-titres aPL (group 4) regarding the number of venous events (p=0.04), recurrence of any thrombotic event (p=0.01), of arterial events (5 vs 0, p=0.02), the occurrence of TIA (p=0.04), DVT (p=0.02) and, when analysing extracriteria manifestations, of peripheral artery disease (p=0.04).

CONCLUSIONS

TGA seems a valuable approach to stratify aPL+ patients according to their risk profile. The differences among different populations of autoantibodies specificities could be considered a translational validation of the increased thrombotic risk of patients with triple or tetra aPL-positivity.

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-β2-glycoprotein I (aβ2GPI) antibody. The presence of LA is assessed using clot-based tests, while the presence of aCL and aβ2GPI 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.

Lupus Anticoagulant Detection under the Magnifying Glass

Diagnosis of antiphospholipid syndrome (APS) requires the presence of a clinical criterion (thrombosis and/or pregnancy morbidity), combined with persistently circulating antiphospholipid antibodies (aPL). Lupus anticoagulant (LA) is one of the three laboratory parameters (the others being antibodies to either cardiolipin or β2-glycoprotein I) that defines this rare but potentially devastating condition. For the search for aCL and aβ2-GP-I, traditionally measured with immunological solid-phase assays (ELISA), several different assays and detection techniques are currently available, thus making these tests relatively reliable and widespread. On the other hand, LA detection is based on functional coagulation procedures that are characterized by poor standardization, difficulties in interpreting the results, and interference by several drugs commonly used in the clinical settings in which LA search is appropriate. This article aims to review the current state of the art and the challenges that clinicians and laboratories incur in the detection of LA.

Added value of antiphosphatidylserine/prothrombin antibodies in the workup of obstetric antiphospholipid syndrome: communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

BACKGROUND

The added value of antiphosphatidylserine/prothrombin antibodies (aPS/PT) in the diagnostic workup of antiphospholipid syndrome (APS) is unclear. Currently, diagnosis of thrombotic APS (TAPS) and obstetric APS (OAPS) requires persistent presence of lupus anticoagulant (LAC), anticardiolipin (aCL) immunoglobulin (Ig) G/IgM, or anti-β2-glycoprotein I (aβ2GPI) IgG/IgM antibodies.

OBJECTIVES

To evaluate the role of aPS/PT IgG and IgM in OAPS.

METHODS

aPS/PT IgG/IgM, aCL IgG/IgM, aβ2GPI IgG/IgM, and LAC were determined in 653 patients (OAPS, TAPS, and controls). In-house aPS/PT cut-off values were calculated, titers and prevalence were compared between OAPS, TAPS, and controls and type of pregnancy morbidity. Sensitivity, specificity, likelihood ratios, and odds ratios (OR) with 95% CI were calculated.

RESULTS

In OAPS, aPS/PT IgG and IgM showed an OR of 4.32 (95% CI, 2.54-7.36) and 3.37 (95% CI, 1.93-5.89), respectively, but the association was not independent of LAC. Prevalence and titers of aPS/PT IgG and IgM were lower in OAPS than in patients with TAPS. aPS/PT were more prevalent and showed higher titers in patients with late pregnancy loss than in patients with early pregnancy loss with a positivity of 86.4% and 39.3%, respectively. Higher aPS/PT titers did not increase the likelihood of having OAPS.

CONCLUSION

The added value of aPS/PT testing in the current diagnostic workup of OAPS seems limited compared with LAC, aCL, and aβ2GPI. aPS/PT might be useful in specific subsets of patients with OAPS. However, future multicentric studies are needed to elucidate the risk of less frequent and most severe obstetrical manifestations.

Direct oral anticoagulant adsorption and laboratory detection of lupus anticoagulant

Direct oral anticoagulants (DOACs) interfere with many coagulation assays, mostly in lupus anticoagulant (LA) detection, causing false positive and negative results. Despite guidelines recommendations, LA testing may be important during anticoagulation when the clinician has to decide whether to prolong or discontinue the drug.

OBJECTIVES

In this study, the effect of activated charcoal (DOAC-Stop, DS) as a DOAC-adsorbent was investigated on samples from DOACs treated and untreated patients.

BASIC METHODS

165 plasma samples with a LA request were collected in three laboratories: 105 were from patients receiving DOACs and 60 were from nonanticoagulated patients with 30 LA negative and 30 LA positive. All coagulation screening assays and LA assays were evaluated before and after DS treatment.

RESULTS

The adsorption technique reduced DOACs concentration below the Lower Limit of Quantification. For nonanticoagulated patients: no significant difference in ratio results of coagulation screening (prothrombin time, activated partial thromboplastin time and thrombin time) and LA tests were observed before and after addition of DS in LA positive and negative patients. Every LA was correctly classified. For anticoagulated patients: a statistically significant difference was found for coagulation screening assays and LA assays. Final LA conclusions changed after DS addition from positive to negative in 58.9% of patients (more frequently with Rivaroxaban) and from negative to positive in 8% of patients (more frequently with Apixaban).

CONCLUSIONS

Our study suggests that DOAC-Stop can be used in daily laboratory practice to remove DOACs interference for a more accurate assessment of LA that is essential for diagnosis and management of APS patients.

Antiphospholipid Antibody Testing for Anti-cardiolipin and Anti-β2 Glycoprotein I Antibodies Using Chemiluminescence-Based Panels

Antiphospholipid (antibody) syndrome (APS) is a prothrombotic condition with increased risk for thrombosis and pregnancy-related morbidity. In addition to clinical criteria related to these risks, APS is characterized by the persistent presence of antiphospholipid antibodies (aPL), as detected in the laboratory using a potentially wide variety of assays. The three APS criteria-related assays are lupus anticoagulant (LA), as detected using clot-based assays, and the solid-phase assays of anti-cardiolipin antibodies (aCL) and anti-β2 glycoprotein I antibodies (aβ2GPI), with immunoglobulin subclasses of IgG and/or IgM. These tests may also be used for the diagnosis of systemic lupus erythematosus (SLE). In particular, APS diagnosis/exclusion remains challenging for clinicians and laboratories because of the heterogeneity of clinical presentations in those being evaluated and the technical application and variety of the associated tests used in laboratories. Although LA testing is affected by a wide variety of anticoagulants, which are often given to APS patients to prevent any associated clinical morbidity, detection of solid-phase aPL is not influenced by these anticoagulants, and this thus represents a potential advantage to their application. On the other hand, various technical issues challenge accurate laboratory detection or exclusion of aPL. This report describes protocols for the assessment of solid-phase aPL, specifically aCL and aβ2GPI of IgG and IgM class by means of a chemiluminescence-based assay panel. These protocols reflect tests able to be performed on the AcuStar instrument (Werfen/Instrumentation Laboratory). Certain regional approvals may also allow this testing to be performed on a BIO-FLASH instrument (Werfen/Instrumentation Laboratory).

An Overview of Laboratory Testing for Antiphospholipid Antibodies

Antiphospholipid antibodies (aPL) represent a group of autoantibodies directed against phospholipids. These antibodies may arise in a number of autoimmune conditions, of which the antiphospholipid (antibody) syndrome (APS) is best recognized. aPL can be detected by various laboratory assays, essentially comprising both solid-phase (immunological) assays and "liquid-phase" clotting assays identifying so-called lupus anticoagulants (LA). aPL are associated with various adverse pathologies, including thrombosis and placental/fetal morbidity and mortality. The type of aPL present, as well as the pattern of reactivity, is variously associated with the severity of the pathology. Thus, laboratory testing for aPL is indicated to help assess the future risk of such events, as well as representing certain "classification" criteria for APS, also used as surrogates for diagnostic criteria. The current chapter overviews the laboratory tests available to measure aPL and their potential clinical utility.

Laboratory Diagnosis of Antiphospholipid Syndrome: Insights and Hindrances

Diagnosis of antiphospholipid syndrome (APS) requires the presence of a clinical criterion (thrombosis and/or pregnancy morbidity), combined with persistently circulating antiphospholipid antibodies (aPL). Currently, laboratory criteria aPL consist of lupus anticoagulant (LAC), anticardiolipin antibodies (aCL) IgG/IgM, and anti-β2 glycoprotein I antibodies (aβ2GPI) IgG/IgM. Diagnosis and risk stratification of APS are complex and efforts to standardize and optimize laboratory tests have been ongoing since the initial description of the syndrome. LAC detection is based on functional coagulation assays, while aCL and aβ2GPI are measured with immunological solid-phase assays. LAC assays are especially prone to interference by anticoagulation therapy, but strategies to circumvent this interference are promising. Alternative techniques such as thrombin generation for LAC detection and to estimate LAC pathogenicity have been suggested, but are not applicable yet in routine setting. For aCL and aβ2GPI, a lot of different assays and detection techniques such as enzyme-linked immunosorbent and chemiluminescent assays are available. Furthermore, a lack of universal calibrators or standards results in high variability between the different solid-phase assays. Other non-criteria aPL such as anti-domain I β2 glycoprotein I and antiphosphatidylserine/prothrombin antibodies have been suggested for risk stratification purposes in APS, while their added value to diagnostic criteria seems limited. In this review, we will describe laboratory assays for diagnostic and risk evaluation in APS, integrating applicable guidelines and classification criteria. Current insights and hindrances are addressed with respect to both laboratory and clinical implications.

Performance Characteristics of DOAC-Remove for Neutralization of the Effects of Apixaban and Rivaroxaban in Lupus Anticoagulant Assays

OBJECTIVES

This study established the performance characteristics of DOAC-Remove for neutralization of the effects of rivaroxaban and apixaban in lupus anticoagulant (LAC) testing.

METHODS

Normal donor, LAC control, and patient samples were spiked with rivaroxaban or apixaban to simulate their effects on the dilute Russell's viper venom time (dRVVT), activated partial thromboplastin time (APTT), and dilute prothrombin time (dPT). Anti-Xa activity was measured after spiking and after DOAC-Remove neutralization. Accuracy, complex precision, and reference interval verification were evaluated.

RESULTS

DOAC-Remove neutralized rivaroxaban and apixaban concentrations as high as 415 ng/mL and 333 ng/mL, respectively. Percentage positive and negative agreement between the baseline and postneutralization interpretations were 75% or higher for the dRVVT and APTT methods but not for the dPT method. Coefficients of variation (CVs) were 10% or less for all assays except the Staclot-LA delta, which had a standard deviation of 2.5 seconds or CV of 25% or less depending on the level. The laboratory's reference intervals were verified for the dRVVT and APTT assays after DOAC-Remove treatment but not for the dPT assays.

CONCLUSIONS

DOAC-Remove appears to have acceptable performance characteristics for neutralizing the effects of rivaroxaban and apixaban in the dRVVT and APTT methods but not in the dPT method.

A multi-laboratory assessment of lupus anticoagulant assays performed on the ACL TOP 50 family for harmonized testing in a large laboratory network

Introduction

Lupus anticoagulant (LA) testing is commonly performed within hemostasis laboratories, and the ACL TOP 50 family of instruments represent a new “single platform” of hemostasis instrumentation. Our aim was to evaluate these instruments and manufacturer reagents or alternatives for utility in LA testing.

Methods

Comparative evaluations of LA testing using newly installed ACL TOPs 550 and 750 as well as comparative assessments with existing “reference,” predominantly Stago, instrumentation, and reagents. Evaluations comprised both dilute Russell viper venom time (dRVVT) and activated partial thromboplastin time (APTT)‐based assays. Establishment of normal reference ranges (NRR).

Results

The HemosIL dRVVT‐based assays showed good comparability with the existing Stago reference method (R > 0.9) and could be considered as verified as fit for purpose. A variety of APTT assays was additionally evaluated for LA utility, and we identified from the assessment good utility of a non‐Werfen solution in Hyphen BioMed Cephen reagents. NRR were established based on ≥120 normal individual plasma samples.

Conclusion

This evaluation of LA reagents on ACL TOP 50 Family instruments identified overall acceptable performance of both dRVVT (Werfen solution) and APTT (non‐Werfen solution) to enable harmonization of LA testing in our large network.

Lupus anticoagulant testing during anticoagulation, including direct oral anticoagulants

Background

Lupus anticoagulants (LA) are one laboratory criterion for classification of antiphospholipid syndrome, with presence of vascular thrombosis and/or pregnancy/fetal morbidity being clinical criteria. The presence of LA is detected (or excluded) by laboratory testing, with the activated partial thromboplastin time and dilute Russell's viper venom time the most commonly used tests. Given the association of thrombosis with LA, it is no surprise that anticoagulants are used to treat or manage such patients.

Objectives

To review and discuss interferences from anticoagulants on LA testing, and strategies to mitigate these.

Methods

This narrative review assessed interference from commonly used anticoagulants, focusing on LA testing while on direct oral anticoagulants (DOACs), including use of DOAC neutralizers.

Results

The classical anticoagulants comprise vitamin K antagonists such as warfarin, and heparins, predominantly unfractionated heparin and low molecular weight heparin (LMWH). DOACs have emerged with favorable efficacy and safety. These comprise two classes: direct anti-thrombin (anti-IIa; dabigatran) or direct anti-Xa (rivaroxaban, apixaban, edoxaban) agents. All anticoagulants affect clotting assays, although there are differences in effects according to anticoagulant and assay. Nevertheless, because of such interferences, anticoagulants can lead to false-negative or false-positive LA findings. Several strategies can mitigate such interferences, including avoidance of testing while patients are on such anticoagulants, temporarily switching to an anticoagulant (i.e., LMWH) with less assay interference, testing for LA at nadir levels of anticoagulants, and/or use of anticoagulant neutralizers.

Conclusion

Whilst the best approach is to avoid LA testing on patients taking anticoagulants; if unavoidable, testing may be facilitated by various mitigating strategies.

Direct oral anticoagulant (DOAC) interference in hemostasis assays

Direct oral anticoagulants (DOACs) are a group of direct coagulation factor inhibitors including both direct thrombin inhibitors and direct factor Xa inhibitors. These medications may cause hemostasis assay interference by falsely increasing or decreasing measured values, depending on the analyte. Considering the potential for DOAC interference in a variety of hemostasis assays is essential to avoid erroneous interpretation of results. Preanalytic strategies to avoid DOAC interference include selecting alternatives to clot-based hemostasis assays in patients taking DOACs when possible and sample collection timed when the patient is off anticoagulant therapy or at the expected drug trough. Clinical laboratories may also provide educational materials that clearly describe possible interferences from DOAC, develop testing algorithms to aid in detection of DOAC in submitted samples, use DOAC-neutralizing agents to remove DOACs before continuing with testing, and write interpretive comments that explain the effects of DOAC interference in hemostasis tests. Using a combination of the described strategies will aid physicians and laboratorians in correctly interpreting hemostasis and thrombosis laboratory tests in the presence of DOACs.

Thrombotic manifestations of VEXAS syndrome

VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome is a recently described autoinflammatory syndrome characterized by diffuse inflammatory manifestations, predisposition to hematological malignancy, and an association with a high rate of thrombosis. VEXAS is attributed to somatic mutations in the UBA1 gene in hematopoietic stem and progenitor cells with myeloid restriction in mature forms. The rate of thrombosis in VEXAS patients is approximately 40% in all reported cases to date. Venous thromboembolism predominates thrombotic events in VEXAS. These are classified as unprovoked in etiology, although systemic and vascular inflammation are implicated. Here, we review the clinical and laboratory characteristics in VEXAS that provide insight into the possible mechanisms leading to thrombosis. We present knowledge gaps in the mechanisms and management of VEXAS-associated thromboinflammation and propose areas for future investigation in the field.

Thrombophilia testing in the era of direct oral anticoagulants

Venous thromboembolism (VTE) is increasingly recognised in primary and secondary care practice. The arrival of direct oral anticoagulants (DOACs) has made the management of VTE easier and more convenient. Some patients established on DOACs may need screening for underlying thrombophilias as certain thrombophilic conditions are known to confer a higher thrombosis risk, although the guidelines for when and how to test for a thrombophilia, especially in a patient taking a DOAC, are unclear. This literature review aims to examine when thrombophilia screening should take place in a patient already taking a DOAC, the effect of DOACs on thrombophilia tests, and analyse whether DOACs are safe and effective in both inherited and acquired thrombophilias.

Laboratory testing for activated protein C resistance: rivaroxaban induced interference and a comparative evaluation of andexanet alfa and DOAC Stop to neutralise interference

Background Investigation of hemostasis is problematic when patients are on anticoagulant therapy. Rivaroxaban especially causes substantial interference, extending many clot-based tests, thereby leading to false positive or negative events. In particular, rivaroxaban affects some assays for activated protein C resistance (APCR). Methods We assessed, in an international setting, cross laboratory (n = 31) testing using four samples to evaluate rivaroxaban induced interference in APCR testing, and whether this interference could be neutralised. The samples comprised: (A) pool of normal plasma (APCR-negative control); (B) this normal pool spiked with rivaroxaban (200 ng/mL) to create rivaroxaban-induced interference (potential 'false' positive APCR event sample); (C) the rivaroxaban sample subsequently treated with a commercial direct oral anticoagulant 'DOAC-neutraliser' (DOAC Stop), or (D) treated with andexanet alfa (200 μg/mL). Testing was performed blind to sample type. Results The rivaroxaban-spiked sample generated false positive APCR results for some, but unexpectedly not most APCR-tests. The sample treated with DOAC Stop evidenced a correction in the rivaroxaban-affected APCR assays, and did not otherwise adversely affect the rivaroxaban 'unaffected' APCR assays. The andexanet alfa-treated sample did not evidence correction of the false positive APCR, and instead unexpectedly exacerbated false positive APCR status with many tests. Conclusions DOAC Stop was able to neutralise any APCR interference induced by rivaroxaban. In contrast, andexanet alfa did not negate such interference, and instead unexpectedly created more false-positive APCR events.

Snake Venoms in Diagnostic Hemostasis and Thrombosis

Snake venoms have evolved primarily to immobilize and kill prey, and consequently, they contain some of the most potent natural toxins. Part of that armory is a range of hemotoxic components that affect every area of hemostasis, which we have harnessed to great effect in the study and diagnosis of hemostatic disorders. The most widely used are those that affect coagulation, such as thrombin-like enzymes unaffected by heparin and direct thrombin inhibitors, which can help confirm or dispute their presence in plasma. The liquid gold of coagulation activators is Russell's viper venom, since it contains activators of factor X and factor V. It is used in a range of clotting-based assays, such as assessment of factor X and factor V deficiencies, protein C and protein S deficiencies, activated protein C resistance, and probably the most important test for lupus anticoagulants, the dilute Russell's viper venom time. Activators of prothrombin, such as oscutarin C from Coastal Taipan venom and ecarin from saw-scaled viper venom, are employed in prothrombin activity assays and lupus anticoagulant detection, and ecarin has a valuable role in quantitative assays of direct thrombin inhibitors. Snake venoms affecting primary hemostasis include botrocetin from the jararaca, which can be used to assay von Willebrand factor activity, and convulxin from the cascavel, which can be used to detect deficiency of the platelet collagen receptor, glycoprotein VI. This article takes the reader to every area of the diagnostic hemostasis laboratory to appreciate the myriad applications of snake venoms available in diagnostic practice.

Laboratory Approaches to Test the Function of Antiphospholipid Antibodies

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder caused by the presence of aPLs (antiphospholipid antibodies, i.e., anti-β₂-glycoprotein I and anti-cardiolipin). Everyday practice in terms of laboratory diagnostics of APS includes determination of aPLs and well-known functional assays assessing for lupus anticoagulant (LA), in turn using various tests. According to recent guidelines, the recommended method for LA identification or exclusion is based on the Russell Viper Venom test and a sensitive activated partial thromboplastin time assay. Despite the fact that LA can be quantified in laboratory practice in this way, LA is still used as a binary parameter that is just one of the risk factors of thrombosis in APS. As of today, there are no other functional assays to routinely assess the risk of thrombosis in APS. It is well-known that APS patients display a wide range of clinical outcomes although they may express very similar laboratory findings. One way to solve this dilemma, could be if antibodies could be further delineated using more advanced functional tests. Therefore, we review the diagnostic approaches to test the function of aPLs. We further discuss how thrombin generation assays, and rotational thromboelastometry tests can be influenced by LA, and how experimental methods, such as flow cytometric platelet activation, surface plasmon resonance, or nano differential scanning fluorimetry can bring us closer to the puzzling interaction of aPLs with platelets as well as with their soluble protein ligand. These novel approaches may eventually enable better characterization of aPL, and also provide a better linkage to APS pathophysiology.

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.

Mixing studies for lupus anticoagulant: mostly yes, sometimes no

Lupus anticoagulants (LAs) represent one manifestation of the clinical condition called antiphospholipid syndrome (APS) and are associated with many adverse clinical outcomes, but primarily with thrombosis and/or pregnancy morbidity. LAs are identified by laboratory testing, principally using clot-based assays based on Russell viper venom time (RVVT) and activated partial thromboplastin time (APTT) test methods. All three of the most recent guidance documents for LA testing recommend using these tests, although they vary in regard to inclusion/exclusion of other test processes. Mixing studies form part of the process of LA identification/exclusion, since in vitro LAs act like coagulation inhibitors. Mixing studies are also supported by all three LA guidance documents, but recommendations vary in regard to relative importance and placement in the LA identification/exclusion algorithm. This Point article takes the position that mixing tests are usually indicated for appropriate identification/exclusion of LAs, but can occasionally be omitted.

Applying index of circulating anticoagulant to mixing tests with lupus anticoagulant screen and confirm reagents can distinguish with high specificity between lupus anticoagulants and direct factor Xa inhibitors

BACKGROUND

Lupus anticoagulants (LA) are detected by prolongation of clotting times for dilute Russell's viper venom time (dRVVT) and activated partial thromboplastin time (APTT) screening tests. Direct oral anticoagulants (DOACs) can interfere with both screening and confirmatory tests. The present study aimed to investigate the influence of direct factor Xa inhibitors (DiXaIs) on screen, confirm and mixing tests and establish a method for differentiation from other sample types.

MATERIALS AND METHODS

A total of 257 samples including nonanticoagulated LA positive, LA positive with DiXaIs, factor deficiency, FVIII inhibitors, warfarin and non-APS DiXaIs were tested. APTT reagents Cephen LS/Cephen and dRVVT reagents LA1/LA2 were used, respectively, to screen/confirm the study group. Index of circulating anticoagulant (ICA) was calculated from clotting times based on the following formula as ICA screening and ICA confirmation. ICA= (1:1 Mix sample - Normal pooled plasma) / Screen patient x 100. An ICA matrix was established which suggested the presence of a DiXaI when both ICA screening and confirmation were above the cut-off. When only ICA screening is elevated, LA is suspected.

RESULTS

Sensitivity and specificity of the ICA matrix were 52.2% and 92.8% for DiXaIs and 38.1% and 96.7% for LA in APTT, and 61.2% and 92.9% for DiXaIs and 22.2% and 88.4% for LA in dRVVT, respectively.

CONCLUSION

The ICA matrix achieved high specificity with a lower apparent sensitivity for DiXaI samples comparatively to other devices but due only to less interferences: the matrix could contribute to differentiating DiXaIs from LA in samples where anticoagulation status is unknown.

In vitro diagnostics for the medical dermatologist. Part II: Hypercoagulability tests

The skin often provides initial clues of hypercoagulability with features such as livedo reticularis, livedo racemosa, retiform purpura, necrosis, and ulcerations. Because these cutaneous manifestations are nonspecific, laboratory testing is often needed to evaluate for underlying causes of hypercoagulability. Importantly, these disorders are reported to be the most common mimicker, resulting in an erroneous diagnosis of pyoderma gangrenosum. Understanding inherent properties of, and indications for, available tests is necessary for appropriate ordering and interpretation of results. Additionally, ordering of these tests in an indiscriminate manner may lead to inaccurate results, complicating the interpretation and approach to management. This second article in this continuing medical education series summarizes information on methodology, test characteristics, and limitations of several in vitro laboratory tests used for the work up of hypercoagulability and vasculopathic disease as it pertains to dermatologic disease.

Antiphospholipid Antibody Profile Stability Over Time: Prospective Results From the APS ACTION Clinical Database and Repository

OBJECTIVE

The APS ACTION Registry studies long-term outcomes in persistently antiphospholipid antibody (aPL)-positive patients. Our primary objective was to determine whether clinically meaningful aPL profiles at baseline remain stable over time. Our secondary objectives were to determine (1) whether baseline characteristics differ between patients with stable and unstable aPL profiles, and (2) predictors of unstable aPL profiles over time.

METHODS

A clinically meaningful aPL profile was defined as positive lupus anticoagulant (LAC) test and/or anticardiolipin (aCL)/anti-β2 glycoprotein-I (anti-β2-GPI) IgG/M ≥ 40 U. Stable aPL profile was defined as a clinically meaningful aPL profile in at least two-thirds of follow-up measurements. Generalized linear mixed models with logit link were used for primary objective analysis.

RESULTS

Of 472 patients with clinically meaningful aPL profile at baseline (median follow-up 5.1 yrs), 366/472 (78%) patients had stable aPL profiles over time, 54 (11%) unstable, and 52 (11%) inconclusive. Time did not significantly affect odds of maintaining a clinically meaningful aPL profile at follow-up in univariate (P = 0.906) and multivariable analysis (P = 0.790). Baseline triple aPL positivity decreased (OR 0.25, 95% CI 0.10-0.64, P = 0.004) and isolated LAC test positivity increased (OR 3.3, 95% CI 1.53-7.13, P = 0.002) the odds of an unstable aPL profile over time.

CONCLUSION

Approximately 80% of our international cohort patients with clinically meaningful aPL profiles at baseline remain stable at a median follow-up of 5 years; triple aPL-positivity increase the odds of a stable aPL profile. These results will guide future validation studies of stored blood samples through APS ACTION Core Laboratories.

Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis: Update of the guidelines for lupus anticoagulant detection and interpretation

This guidance focuses on methodological aspects of lupus anticoagulant (LA) testing, as well as interpretation of results for clinicians. The main changes in how to test for LA compared with the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee 2009 guidelines, in the preanalytical phase are more detailed recommendations on how to handle testing in anticoagulated patients, and the timing of testing. Also, routine coagulation tests are advised to obtain more information on the coagulation background of the patient, and when necessary, anti-Xa activity measurement for heparins or specific assays for direct oral anticoagulants should be performed. The three-step procedure with two test systems (diluted Russell's viper venom time and activated partial thromboplastin time [aPTT]) is essentially not changed. Silica remains the preferable activator in the aPTT assays, but ellagic acid is not excluded. We advise simultaneous performance of the mixing and confirmatory step, in each sample with a prolonged screening test. The confirmatory step can also be performed on a mixture of patient plasma and normal pooled plasma. Cutoff values should be established in-house on at least 120 normals, with transference of the manufacturer's cutoffs as an alternative. Reporting of results has not been changed, although more attention is focused on what clinicians should know. Patient selection for LA testing has been expanded.

Comprehensive review of the impact of direct oral anticoagulants on thrombophilia diagnostic tests: Practical recommendations for the laboratory

There is a laboratory and clinical need to know the impact of direct oral anticoagulants (DOACs) on diagnostic tests to avoid misinterpretation of results. Although the regulatory labelling documents provide some information about the influences of each DOAC on diagnostic tests, these are usually limited to some of the most common tests and no head to head comparison is available. In this paper, we report the impact of DOACs on several thrombophilia tests, including assessment of antithrombin, protein S and protein C activity assays, detection of activated protein C resistance and assays used for lupus anticoagulant. Results are compared and discussed with data obtained from literature. The final goal of this comprehensive review is to provide practical recommendations for laboratories to avoid misdiagnosis due to oral direct factor Xa (FXa) or IIa (FIIa) inhibitors. Overall, oral direct FXa (apixaban, betrixaban, edoxaban and rivaroxaban) and FIIa (dabigatran) antagonists may affect clot-based thrombophilia diagnostic tests resulting in false-positive or false-negative results. An effect on FIIa-based thrombophilia diagnostic tests is observed with dabigatran but not with anti-FXa DOACs and conversely for FXa-based thrombophilia diagnostic tests. No impact was observed with antigenic/chromogenic methods for the assessment of protein S and C activity. In conclusion, interpretation of thrombophilia diagnostic tests results should be done with caution in patients on DOACs. The use of a device/chemical compound able to remove or antagonize the effect of DOACs or the development of new diagnostic tests insensitive to DOACs should be considered to minimize the risk of false results.

Unveiling the complex effects of direct oral anticoagulants on dilute Russell's viper venom time assays

INTRODUCTION

Dilute Russell viper venom time (dRVVT) assays can be affected by direct oral anticoagulants (DOACs), which may cause false-positive results. However, there are conflicting results indicating significant differences between different reagents and DOACs.

OBJECTIVES

To evaluate the effect of DOACs on dRVVT assays.

MATERIAL AND METHODS

Samples were prepared by adding DOAC (dabigatran, rivaroxaban, apixaban, or edoxaban) to pooled normal plasma in the concentration range 0 to 800 µg/L. Six integrated dRVVT reagents were used, all composed of a screen assay (low phospholipid content) and a confirm assay (high phospholipid content). The screen/confirm dRVVT results were expressed as normalized ratios. To further evaluate the observed differences between tests and DOACs, addition of synthetic phospholipids was used.

RESULTS

The dRVVT ratios increased dose dependently for all DOACs, with four of the six tests and the DOAC rivaroxaban having the greatest effect. With one test, the ratios were almost unaffected with increasing DOAC concentration, whereas another test revealed a negative dose dependency for all DOACs. Variable DOAC effects can be explained by different effects on dRVVT screen and confirm clotting time. Adding synthetic phospholipids to samples containing rivaroxaban resulted in greatly reduced screen clotting times and thereby lower calculated dRVVT ratios.

CONCLUSIONS

There is a great variability in the dRVVT test result with different DOACs. The dRVVT ratios are unaffected for some reagents and this can be explained by an equal dose-dependent effect on both screen and confirm assays. The phospholipid type and content of the different reagents may contribute to the observed differences.

Direct oral anticoagulant adsorption: Impact on lupus anticoagulant testing-Review of the literature and evaluation on spiked and patient samples

BACKGROUND

Direct oral anticoagulants (DOACs) interfere with lupus anticoagulant (LAC) testing. DOAC-Stop (D-S) represents a preanalytical strategy to cope with this issue.

OBJECTIVES

To assess D-S's ability to remove DOACs from plasma and overcome DOAC interference in LAC assays and to evaluate D-S's applicability in a representative patient cohort with routine LAC request.

METHODS

Apixaban (30-933 ng/mL), edoxaban (31-1060 ng/mL), rivaroxaban (35-1020 ng/mL), and dabigatran (20-360 ng/mL) were spiked to normal plasma. Aliquots were treated with D-S or untreated before DOAC and LAC testing. Patient samples containing DOAC (n = 43), vitamin K antagonists (n = 25), heparins (n = 21), or no anticoagulants (n = 63) were tested for LAC before and after D-S.

RESULTS

Spiking experiments revealed false-positive LAC from low concentrations of DOACs except for apixaban. Following D-S, DOAC levels were below lower limits of quantification, except for apixaban at the highest concentration, and no false-positive LAC was obtained. DOAC levels were below lower limits of quantification after D-S in 39/43 DOAC-containing patient samples. For 23/29 LAC-positive DOAC-containing samples, LAC tests became negative after D-S, whereas 3/6 samples remaining positive were from patients with (high probability for) antiphospholipid syndrome. In the non-DOAC-treated groups, LAC changed from positive to negative in 10 and vice versa in 2 cases.

CONCLUSIONS

D-S limits DOAC interference in LAC assays. DOAC concentration measurement should be performed in D-S treated samples because incomplete removal may occur. Applying D-S to vitamin K antagonist-containing, heparin-containing, or not-anticoagulated samples may lead to erroneous LAC results. Therefore, D-S should only be used in plasma from DOAC-treated patients.

Antiphospholipid Syndrome Committee of the Brazilian Society of Rheumatology position statement on the use of direct oral anticoagulants (DOACs) in antiphospholipid syndrome (APS)

BACKGROUND

The term Direct Oral Anticoagulants (DOACs) refers to a group of drugs that inhibit factor Xa or thrombin. Even though their use for treating different thrombotic or prothrombotic conditions is increasing recently, there is no compelling evidence indicating that those medications are safe in all antiphospholipid syndrome (APS) patients.

METHODOLOGY

To address this issue, specialists from the Antiphospholipid Syndrome Committee of the Brazilian Society of Rheumatology performed a comprehensive review of the literature regarding DOACs use in APS to answer the three following questions: (1) potential mechanisms of action of these drugs that could be relevant to APS pathogenesis, (2) DOACs interference on lupus anticoagulant testing, and (3) the efficacy of DOACs in APS.

POSITION STATEMENT

After critically reviewing the relevant evidence, the authors formulated 8 Position Statements about DOACs use in APS.

CONCLUSION

DOACs should not be routinely used in APS patients, especially in those with a high-risk profile (triple positivity to aPL, arterial thrombosis, and recurrent thrombotic events). In addition, DOACs interferes with LA testing, leading to false-positive results in patients investigating APS.

Reducing the effect of DOAC interference in laboratory testing for factor VIII and factor IX: A comparative study using DOAC Stop and andexanet alfa to neutralize rivaroxaban effects

INTRODUCTION

Investigation of factors (F) VIII and IX is common, with testing important for diagnosis or exclusion of haemophilia A or B, associated acquired conditions and factor inhibitors. Rivaroxaban, a common direct anti-Xa agent, causes significant interference in clotting assays, including substantial false reduction of factor levels.

AIM

To assess whether rivaroxaban-induced interference of FVIII and FIX testing could be neutralized.

MATERIALS AND METHODS

An international, cross-laboratory exercise for FVIII (n = 84) and FIX (n = 74), using four samples: (A) pool of normal plasma; (B) pool spiked with rivaroxaban (200 ng/mL); (C) rivaroxaban sample subsequently treated with 'DOAC Stop' and; (D) rivaroxaban sample treated with andexanet alfa (200 μg/mL). Testing performed blind to sample type.

RESULTS

All laboratories reported normal FIX and 94% reported normal FVIII in the pool sample. Instead, 55% and 95%, respectively, reported abnormal FIX and FVIII levels for the rivaroxaban sample. DOAC Stop treatment evidenced a correction in most laboratories (100% reported normal FIX and 86% normal FVIII). Andexanet alfa provided intermediate results, with many laboratories still reporting abnormal results (59% for FVIII, 18% for FIX). We also identified reagent-specific issues.

CONCLUSIONS

As expected, rivaroxaban caused false low values of FVIII and FIX. This might lead to increased testing to identify the cause of low factor levels and potentially lead to false identification of (mild) haemophilia A or B if unrecognized by clinicians/laboratories. DOAC Stop effectively neutralized the rivaroxaban effect, but andexanet alfa less so, with reagent-related effects evident, and thus, false low values sometimes persisted.

Escaping the catch 22 of lupus anticoagulant testing

High-risk patients with antiphospholipid syndrome (APS) experience increased risk of thrombosis when treated with direct oral anticoagulant (DOAC) therapy compared with warfarin. It is essential to establish the APS diagnosis to choose therapy and determine treatment duration. It requires testing for antiphospholipid antibodies, including lupus anticoagulant (LAC). In this viewpoint, we discuss the options for timing of LAC testing, which includes testing before starting anticoagulant treatment (DOAC or warfarin), after switching to heparin or after withdrawal of anticoagulant treatment. DOACs interfere with LAC testing and recommendations emerge stating not to conduct on-therapy LAC testing. All approaches are to some extent currently practised, but have limitations and the area is therefore seemingly a catch 22. We put forward that the anticoagulant effect of DOAC can be eliminated in the laboratory and therefore patients can be tested on-therapy. While it may not eliminate all cases of interference, it could aid the interpretation in these situations and this approach is attractive from the patient and clinician’s perspective. Nevertheless, to prevent misdiagnosis the diagnostic workup for APS requires collaboration between the clinician and the laboratory. We advocate for standardisation in laboratory and clinical practice when diagnosing APS.

The effect of unfractionated heparin, enoxaparin, and danaparoid on lupus anticoagulant testing: Can activated carbon eliminate false-positive results?

BACKGROUND

Heparins and heparinoids interfere with functional clotting assays used for lupus anticoagulant (LAC) detection. However, current guidelines for LAC testing do not provide clear guidance on this matter.

OBJECTIVES

We aimed to assess to effect of unfractionated heparin (UFH), enoxaparin, and danaparoid on LAC assays over broad anti-Xa activity ranges and to evaluate whether activated carbon (AC) is able to neutralize these effects.

METHODS

UFH (0.1-3.0 IU/mL), enoxaparin (0.2-2.9 IU/mL), and danaparoid (0.6-2.2 IU/mL) were spiked to normal pooled plasma. AC was added at multiple activity levels. Anti-Xa assays and LAC tests were performed on all samples using Stago analyzers and reagents.

RESULTS

Abnormal activated partial thromboplastin time (APTT) screening and mixing tests were obtained at the lowest levels for all compounds. Abnormal APTT confirmation tests were seen from 2.5 and 1.9 anti-Xa IU/mL for enoxaparin and danaparoid, respectively. Abnormal dilute Russell's viper venom test (dRVVT) screening tests were obtained from 1.6, 1.4, and 1.1 anti-Xa IU/mL for UFH, enoxaparin, and danaparoid, respectively. Mixing tests were abnormal from 2.5 and 1.3 anti-Xa IU/mL for enoxaparin and danaparoid, respectively. Abnormal dRVVT confirmation results were seen for danaparoid only from 1.9 anti-Xa IU/mL. AC was unable to neutralize anti-Xa activity in plasma and overcome the effect of the tested anticoagulants on LAC assays but may cause prolongation of APTT clotting times.

CONCLUSIONS

UFH, enoxaparin, and danaparoid clearly affected LA tests; however, false-positive LAC conclusions were obtained at supratherapeutic enoxaparin and danaparoid levels only. AC may prolong APTT screen clotting times, requiring 3-step testing to avoid potential misdiagnosis of LAC.

Coagulation mixing studies: Utility, algorithmic strategies and limitations for lupus anticoagulant testing or follow up of abnormal coagulation tests

Coagulation testing underpins the investigation of hemostasis and/or monitoring of anticoagulation therapy for prevention and/or treatment of thrombosis related pathology. Assessment of coagulation results requires comparison against a normal reference range or interval (NRR/NRI). Results flagged as "abnormal" (ie, above the NRR/NRI for patients not on anticoagulant therapy), typically require further evaluation. eg, follow up or reflexive testing is used to identify the reason for prolongation, especially when supported by clinical context (eg, bleeding). Mixing tests may have utility to help identify the pathway of follow-up testing (ie, towards investigation of factor deficiencies, or else inhibitors), and are also useful for investigation of lupus anticoagulants (LA). In general, mixing tests that "correct" tend to suggest the presence of factor deficiencies, where as those that do not correct suggest the presence of "inhibitors". Various approaches can be used to identify correction/non-correction, and all have strengths and limitations. Furthermore, eventual identification of causal factor deficiencies or even "inhibitors" may (eg, factor VIII or IX deficiencies or inhibitors) or may not (eg, factor XII deficiency) be clinically important. Ultimately, mixing studies performed in view of appropriate clinical scenarios (eg, bleeding patient) and for LA investigations in symptomatic patients will have best utility.

The Russell viper venom time (RVVT) test for investigation of lupus anticoagulant (LA)

Lupus anticoagulants (LAs) are a laboratory representation of the clinical syndrome of antiphospholipid syndrome (APS), and can also arise in other pathological states. Laboratory testing for LA is complex and three separate recent guidelines have been published. One test, the Russell viper venom time (RVVT), is the mandated laboratory test for inclusion in LA identification/exclusion in all three guidance documents. This is because the the RVVT is recognized to have great sensitivity for LA, with this generally recognized to be greater than that of most other LA screening assays. However, the RVVT is also very sensitive to the presence of many anticoagulant drugs, which diminishes its specificity for LA. Various strategies can be used to improve LA specificity and reduce anticoagulant assay interference.