DOAC-Stop in lupus anticoagulant testing: Direct oral anticoagulant interference removed in most samples

Dilemmas in the diagnosis and management of antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thrombosis (which may be venous, arterial, or microvascular) and/or pregnancy morbidity in association with persistently positive antiphospholipid antibodies. Although thrombosis and pregnancy morbidity are the main clinical criteria for a diagnosis of APS in the revised Sapporo (Sydney) criteria, recently published American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for APS have significantly refined the diagnostic algorithm to include a scoring system clustered into 6 clinical domains (macrovascular venous thromboembolism, macrovascular arterial thrombosis, microvascular thrombosis, obstetric, cardiac valve, and hematologic). Diagnosis of APS is complicated by the fact that significant heterogeneity exists in patients' clinical presentation, underlying vascular risk factors, and methods of detecting antiphospholipid antibodies. Despite the autoimmune nature of APS, anticoagulation remains the main strategy for secondary prevention of thrombosis. Furthermore, optimal antithrombotic treatment in APS patients with arterial thrombosis remains controversial due to a paucity of data from randomized controlled studies. In this paper, we present 2 cases and highlight the diagnostic and therapeutic challenges they pose and how we approach them in the light of current evidence.

Simplified Method for Removing Direct Oral Anticoagulant Interference in Mechanical Coagulation Test Systems-A Proof of Concept

BACKGROUND

Direct oral anticoagulants (DOACs) cause unwanted interference in various hemostasis assays, including lupus anticoagulant (LA) testing, where false positive and false negative identification may occur. DOAC Stop (DS) is an activated charcoal (AC) product used to specifically and effectively adsorb DOACs from test plasma. This process normally requires plasma treatment, centrifugation and plasma separation prior to tests, but inexperienced operators may also inadvertently transfer residual AC particles, thereby potentially adversely affecting clot detection.

METHODS

We hypothesized that residual DS might not be problematic for mechanical clot detection. We therefore investigated the potential impact of DS and a new DS liquid (DS-L) product on clotting tests using a mechanical clot detection system. Varying concentrations of DS were added to normal and abnormal plasmas with and without DOAC presence. Clotting tests including PT, APTT and dRVVT were performed directly in the analyzer without plasma/DS centrifugation.

RESULTS

DS up to double the recommended treatment level had only minor effects on all test results, despite completely obscuring visibility in the plasma/reagent mix. This confirms that the centrifugation step may be able to be omitted when using mechanical detection systems.

CONCLUSIONS

Should DS carryover into treated plasmas occur, this should not cause issues with testing performed on mechanical clot-sensing devices. Moreover, we hypothesize that DS can be used directly in these systems, without the need for centrifugation, thereby simplifying its many potential applications.

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.

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 syndrome: advances in diagnosis, pathogenesis, and management

Antiphospholipid syndrome (APS) is a thrombo-inflammatory disease propelled by circulating autoantibodies that recognize cell surface phospholipids and phospholipid binding proteins. The result is an increased risk of thrombotic events, pregnancy morbidity, and various other autoimmune and inflammatory complications. Although antiphospholipid syndrome was first recognized in patients with lupus, the stand alone presentation of antiphospholipid syndrome is at least equally common. Overall, the diagnosis appears to affect at least one in 2000 people. Studies of antiphospholipid syndrome pathogenesis have long focused on logical candidates such as coagulation factors, endothelial cells, and platelets. Recent work has shed light on additional potential therapeutic targets within the innate immune system, including the complement system and neutrophil extracellular traps. Vitamin K antagonists remain the mainstay of treatment for most patients with thrombotic antiphospholipid syndrome and, based on current data, appear superior to the more targeted direct oral anticoagulants. The potential role of immunomodulatory treatments in antiphospholipid syndrome management is receiving increased attention. As for many systemic autoimmune diseases, the most important future direction is to more precisely identify mechanistic drivers of disease heterogeneity in pursuit of unlocking personalized and proactive treatments for patients.

A Review of Systemic Hematological Manifestations and Stent Thrombosis

Stent thrombosis (ST) has significant morbidity and mortality following percutaneous coronary intervention (PCI). ST is uncommon making the identification of nonprocedural predictors challenging. Numerous case reports of ST in both benign and malignant hematological conditions exist. Given ST could be a Herald event of an undiagnosed condition and condition-specific treatment may be available, it is important to consider specialist testing in an unexplained ST. This review included a case presentation of ST in previously undiagnosed paroxysmal nocturnal hemoglobinuria (PNH) and a literature review of ST in other acquired thrombophilias including myeloproliferative disorders (MPNs), antiphospholipid syndrome, hematological malignancies, and heparin-induced thrombocytopenia (HIT). Inherited thrombophilias and common pitfalls in thrombophilia and coagulation testing are also discussed. The cardiac-hematology landscape is becoming increasingly complex and there is a paucity of how to best manage ST in these patients. There is clear variability in practice and the use of multidisciplinary input between cardiologists and hematologists is essential.

Novel Ex Vivo DOAC Removal Methods Reduce Interference in Lupus Anticoagulant Testing

Direct oral anticoagulants (DOAC) interfere in laboratory coagulation testing. The aim here was to study how commercial DOAC removal methods, DOAC Filter^® and DOAC-Stop™, perform to eliminate DOAC concentrations and false positive results in lupus anticoagulant (LAC) testing. We acquired 50 patient samples with high concentrations of DOACs: apixaban (n = 18, range 68–572 ng/mL), dabigatran (n = 8, range 47–154 ng/mL), edoxaban (n = 8, range 35–580 ng/mL) and rivaroxaban (n = 16, range 69–285 ng/mL). DOACs were removed ex vivo with either DOAC Filter^® (n = 28) or DOAC-Stop™ (n = 22). Additionally, commercial control and calibrator samples were studied (n = 13 for DOAC Filter^®, n = 14 for DOAC-Stop™). LAC screening was performed before and after DOAC removal. Both DOAC Filter^® and DOAC-Stop™ were effective in removing DOAC concentrations in samples: DOAC concentrations decreased to median of 0 ng/mL (range 0–48 ng/mL). Only one sample had more than residual 25 ng/mL of DOAC (apixaban). Before DOAC removal, 96% (48/50) of patient samples and over 90% (12/13 DOAC Filter^®, 13/14 DOAC-Stop™) of control/calibrator samples were positive in the LAC screening. In patient samples, LAC screening turned negative in 61% (17/28) after DOAC Filter^® and 45% (10/22) after DOAC-Stop™ treatment. All control samples became negative after DOAC removal. In conclusion, DOAC removal ex vivo reduces false positives in LAC screening. DOAC removal halved the need for confirmation or mixing tests- Although a subset of patients would require further testing, DOAC removal reduces unnecessary repeated LAC testing.

Testing for Lupus Anticoagulants

Lupus anticoagulant (LA) is one of the three criteria antiphospholipid antibodies (aPLs) employed in classification, and by default diagnosis, of antiphospholipid syndrome (APS). Detection of LA is not via calibrated assays but is based on functional behavior of the antibodies in a medley of coagulation assays. A prolonged clotting time in a screening test is followed by demonstration of phospholipid dependence and inhibitory properties in confirmatory and mixing tests, respectively, which are modifications of the parent screening test. Complications arise because no single screening test is sensitive to every LA, and no test is specific for LA, because they are prone to interference by other causes of elevated clotting times. Several screening tests are available but the pairing of dilute Russell's viper venom time (dRVVT) with LA-sensitive activated partial thromboplastin time (aPTT) is widely used and recommended because it is proven to have good detection rates. Nonetheless, judicious use of other assays can improve diagnostic performance, such as dilute prothrombin time to find LA unreactive with dRVVT and aPTT, and the recently validated Taipan snake venom time with ecarin time confirmatory test that are unaffected by vitamin K antagonist and direct factor Xa inhibitor anticoagulation. Expert body guidelines and their updates have improved harmonization of laboratory practices, although some issues continue to attract debate, such as the place of mixing tests in the medley hierarchy, and areas of data manipulation such as assay cut-offs and ratio generation. This article reviews current practices and challenges in the laboratory detection of LA.

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.

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 removal by a DOAC filter: Impact on lupus anticoagulant testing - Evaluation on spiked and patient samples

Background

DOAC Filter (DF) is a new device to overcome interference in lupus anticoagulant (LAC) testing by direct oral anticoagulants (DOACs).

Objectives

We evaluated DOAC removal from plasma and elimination of DOAC interference in LAC testing by DF, and impact of DF on LAC assays in a representative patient cohort, including a comparison with DOAC-Stop (DS).

Methods

Normal pooled plasma (NPP) was spiked with increasing concentrations of apixaban, rivaroxaban, edoxaban, and dabigatran. DOAC and LAC was measured on untreated, DF-treated, and DS-treated spiked samples. Coagulation parameters and thrombin generation were measured on patient samples (n = 20) before and after DF. Patients treated with DOAC, vitamin K antagonist, or heparin and nonanticoagulated patient samples (n = 139) were tested for LAC before and after DF.

Results

In spiked NPP, levels were below the lower limit of quantification (LLoQ) after DF/DS treatment for all DOAC concentrations. Following DF, levels were below LLoQ for 53 of 56 DOAC-containing patient samples. Twenty-eight of 33 LAC-positive DOAC-containing samples became negative after filtration, whereas 5 remained LAC-positive (1/5 from a patient with antiphospholipid syndrome [APS]). Four LAC-positive DOAC-containing samples (from patients without APS), became negative after filtration, whereas they remained LAC positive after DS. In the non-DOAC patient groups following DF, LAC changed from positive to negative in 8 (due to a procoagulant effect) and vice versa in 2 cases.

Conclusion

DF reduces DOAC interference in LAC testing. As incomplete DOAC removal may occur, DOAC measurements should be performed after filtration. A procoagulant effect after filtration may lead to erroneous LAC results in non-DOAC-containing samples. Therefore, using DF should be restricted to DOAC-containing samples.

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.

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.