International multicenter, multiplatform study to validate Taipan snake venom time as a lupus anticoagulant screening test with ecarin time as the confirmatory test: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

Abstract

Background Lupus anticoagulant (LA) assays are compromised in anticoagulated patients, and existing strategies to overcome the interferences have limitations. The prothrombin‐activating Taipan snake venom time (TSVT) screening test and ecarin time (ET) confirmatory test are innately insensitive to vitamin K antagonists (VKA) and direct factor Xa inhibitors (DFXaI). Objectives Validate standardized TSVT/ET reagents for LA detection, in a multicenter, multiplatform study. Patients/Methods Six centers from four countries analyzed samples with TSVT/ET from 81 nonanticoagulated patients with LA, patients with established antiphospholipid syndrome (APS), and proven persistent LA who were either not anticoagulated (n = 120) or were anticoagulated with VKAs (n = 180) or DFXaIs (n = 71). Additionally, 339 nonanticoagulated LA‐negative patients, and 575 anticoagulated non‐APS patients (172 VKA, 403 DFXaI) were tested. Anticoagulant spiking experiments were performed and 112 samples containing potential interferences (i.e., direct thrombin inhibitors) were tested. Results were evaluated against locally derived cutoffs. Imprecision was evaluated. Results Cutoffs were remarkably similar despite use of different analyzers and donor populations. Cutoffs for TSVT ratio, ET ratio, percent correction, and normalized TSVT ratio/ET ratio ranged between 1.08 and 1.10, 1.09 and 1.12, 9.3% and 14.8%, and 1.10 and 1.15, respectively. Coefficients of variation for TSVT and ET ratios were ≤5.0%. TSVT/ET exhibited sensitivity, specificity, and negative and positive predictive values of 78.2%/95.0%/86.3%/91.5%, respectively, with established APS as the LA‐positive population, and 86.9%/95.0%/76.8%/97.4%, respectively, with triple‐positive APS. Interference was seen with direct thrombin inhibitors, unfractionated heparin, and low molecular weight heparins, but not VKAs or DFXaIs. Conclusions TSVT/ET are validated for LA detection in nonanticoagulated patients and those on VKAs or DFXaIs.

Direct oral anticoagulants‐Remove versus Taipan snake venom time for detection of a lupus anticoagulant in patients taking oral direct factor Xa inhibitors

“…The TSVT has been previously investigated as a method to detect an LA in patients on DFXaIs. 10 , 13 , 18 , 19 , 20 , 21 The advantage of a TSVT/ET assay is that no preanalytical inactivation step is necessary for LA detection on DFXaI because prothrombin activation bypasses the effects of factor Xa inhibitors. 13 The ISTH has previously issued guidance within this area and concluded that there was “no conclusive independent evidence reported on their diagnostic efficacy” and that studies had small numbers of patients mostly on rivaroxaban with challenges in kit standardization and availability likely to limit widespread utility and generalizability.…”

“… 10 , 13 , 18 , 19 , 20 , 21 The advantage of a TSVT/ET assay is that no preanalytical inactivation step is necessary for LA detection on DFXaI because prothrombin activation bypasses the effects of factor Xa inhibitors. 13 The ISTH has previously issued guidance within this area and concluded that there was “no conclusive independent evidence reported on their diagnostic efficacy” and that studies had small numbers of patients mostly on rivaroxaban with challenges in kit standardization and availability likely to limit widespread utility and generalizability. 6 This has recently been challenged in a multicenter, multiplatform publication by the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies, which validated the TSVT/ET for patients taking DFXaI.…”

“… 6 This has recently been challenged in a multicenter, multiplatform publication by the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies, which validated the TSVT/ET for patients taking DFXaI. 13 What remains unclear is whether the discrepancy in LA detection between the techniques we have investigated are because of (i) complex effects of plasma manipulation by DOAC Remove; (ii) differential sensitivity of the TSVT/ET, APTT, and dRVVT for detecting LA (because of the heterogenous nature of LA antibodies, the sensitivity of the TSVT/ET for all LA was 72% and 78% in confirmed APS cases and 87% in triple‐positive [i.e., LA, cardiolipin, and beta‐2‐glycoprotein I positive] APS cases in the recent ISTH SSC publication regarding this 13 ); and (iii) confounding of the anticoagulant effects on assays or combinations thereof. In theory, the dRVVT/APTT could be more sensitive to detecting an LA compared with TSVT/ET because there are two assays; however, this was not borne out in the comparison of the two techniques (Table 3 ).…”

“…TSVT/ET (Diagnostic Reagents Ltd) was performed in accordance with the manufacturer's instructions as previously described. 13 TSVT/ET test ratio and APTT test ratio were tested as integrated testing systems. Ratios for all assays were calculated using the reference range mean clotting times.…”

Snake Venoms in Diagnostic Hemostasis and Thrombosis

“…[170][171][172] A recent multi-centre study has validated TSVT/ET testing in non-anticoagulated patients and those anticoagulated with VKAs and all DFXaIs. 173 Although adsorbents for direct oral anticoagulant (DOAC) removal from plasma are available, they have their own limitations, and cannot mitigate for the effects of VKA anticoagulation. 158,174,175 Of potential clinical import is that T/E ratio and TSVT/ET testing have been reported to detect small numbers of LA unreactive in dRVVT and aPTT.…”