Performance of direct oral anticoagulant (DOAC) testing by hemostasis laboratories: The Australasian/Asia-Pacific experience.

INTRODUCTION: Direct oral anticoagulants (DOACs) reflect anticoagulation agents given to treat or prevent thrombosis, having largely replaced vitamin K antagonists (VKAs) such as warfarin. DOACs are given in fixed daily doses and generally do not need monitoring. However, there may be a variety of reasons that justify measurement of plasma DOAC levels in individual patients. METHODS: We report updated findings for DOAC testing in our geographic region, using recent data from the RCPAQAP, an international external quality assessment (EQA) program, currently with some 40-60 participants in each of the different DOAC (rivaroxaban, apixaban, dabigatran) modules, to assess laboratory performance in this area. Data has been assessed for the past 5 years (2019-2023 inclusive), with 20 samples each per DOAC. RESULTS: Data shows a limited repertoire of assays in use, and mostly consistency in reported numerical values when assessing proficiency samples. Available assays mostly comprised reagents from four manufacturing suppliers. There was good consistency across what participants identified as 'DOAC detected', but some variability when participants attempted to grade DOAC levels as low vs moderate vs high. Inter-laboratory/method coefficient of variation (CVs) were generally <15% for each DOAC, when present at >100 ng/mL. CONCLUSION: We hope our findings, reflecting on mostly consistent reporting of DOAC levels and interpretation provides reassurance for clinicians requesting these measurements, and helps support their implementation in regions where there is a paucity of test availability.

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.

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.

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.

Evaluating errors in the laboratory identification of von Willebrand disease using contemporary von Willebrand factor assays.

von Willebrand disease (VWD) arises from deficiency and/or defects of von Willebrand factor (VWF). Assessment requires test panels, including VWF activity and antigen. Appropriate diagnosis including differential identification of qualitative versus quantitative defects remains problematic but has important management implications. Data using a large set (n=27) of varied plasma samples comprising both quantitative VWF deficiency ('Type 1 and 3') vs qualitative defects ('Type 2') tested in a cross-laboratory setting have been evaluated to assess contemporary VWF assays for utility to differentially identify sample types. Different VWF assays and activity/antigen ratios showed different utility in VWD and type identification. Identification errors were linked to assay limitations, including variability, and laboratory issues (e.g., test result misinterpretation). Quantitative deficient (type 1) samples were misinterpreted as qualitative defects (type 2) on 35/467 occasions (7.5% error rate); 11.4% of these errors were due to laboratories misinterpreting their own data, which was instead consistent with quantitative deficiencies. Conversely, qualitative defects were misinterpreted as quantitative deficiencies at a higher error rate (14.3%), but this was more often due to laboratories misinterpreting their data (40% of errors). For test-associated errors, VWF:RCo and VWF:GPIbM were associated with the highest variability and error rate, which was many-fold higher than that using VWF:CB. Chemiluminescence ('CLIA') procedures were associated with lowest inter-laboratory variability and errors overall. These findings in part explain the high rate of errors associated with VWD diagnosis. VWF:GPIbM showed a surprisingly high rate of test associated errors, whilst CLIA procedures performed best overall.

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.

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.

Neutralising rivaroxaban induced interference in laboratory testing for lupus anticoagulant (LA): A comparative study using DOAC Stop and andexanet alfa.

INTRODUCTION: Lupus anticoagulant (LA) investigation in patients on anticoagulant therapy is problematic. Rivaroxaban in particular causes significant interference, prolonging both LA screening and confirmation tests, and falsely raising LA screen/confirm ratios, leading to potential false identification of LA. The Russell Viper Venom Time (RVVT) assay, key to the investigation of LA, is especially sensitive to rivaroxaban. MATERIALS AND METHODS: We assessed cross laboratory (n = 82) testing of four samples to investigate whether rivaroxaban induced interference in LA testing could be neutralised. Testing was performed blind to sample type. The samples comprised: (A) A pool of normal plasma (LA-negative control); (B) sample A spiked with rivaroxaban (200 ng/mL) to create rivaroxaban-induced interference (LA 'false' positive sample); (C) sample B subsequently treated with a commercial 'DOAC-neutraliser' (DOAC Stop); (D) sample B treated with andexanet alfa (200 µg/mL). RESULTS: As expected, the rivaroxaban-spiked sample (B) caused prolongation of most LA-tests, and also generated a falsely prolonged RVVT screen/confirm ratio (median 1.37, compared to 0.97 for sample A). The sample (C) treated with DOAC Stop evidenced a correction in LA-test clotting times, as well as neutralising the false positive LA (median RVVT screen/confirm ratio of 0.99). Although the andexanet alfa treated sample (D) also yielded a low median RVVT screen/confirm ratio of 0.88, it did not fully correct LA-test clotting times. Consistent with test findings, all laboratories interpreted samples A and C as being LA-negative. For sample B (rivaroxaban), 45.3% identified this as LA positive, and 38.7% identified LA interference. Most (61.3%) also identified sample D as LA negative, with the remainder (38.7%) identifying LA interference. CONCLUSIONS: DOAC Stop was able to neutralise the false LA activity induced by rivaroxaban, both in terms of clot-times and LA ratios. In contrast, whilst andexanet alfa negated the rivaroxaban-prolonged LA-ratio, it did not fully correct clot-times, leaving some residual LA interference, and requiring additional testing to investigate prolonged clotting times.