Background Dilute Russell's viper venom time (dRVVT) is indispensible in lupus anticoagulant (LA) detection yet commercial reagents from different suppliers perform variably, no gold standard assays exist and therapeutic anticoagulation interference is problematic. Objective The objective of this study was to compare a new formulation dRVVT with two currently available dRVVTs. Materials and methods Life Diagnostics (LD) dRVVT and Stago PTT-LA were routinely used for lupus anticoagulant detection, plus Taipan snake venom time/ecarin time (TSVT/ET) for patients on warfarin or rivaroxaban. Siemens dRVVT and the new HYPHEN BioMed (HBM) dRVVT were tested with 193 patient samples. Group 1, 59 non-anticoagulated patients (NAPs) LA-positive in LD dRVVT; Group 2, 15 PTT-LA-positive/dRVVT-negative NAPs; Group 3, 24 LA-positive warfarinized patients; Group 4, 13 patients on rivaroxaban; Group 5, 62 LA-negative thrombotic NAPs; Group 6, 20 warfarinized, non-antiphospholipid syndrome patients. Results Accepting that the Life Diagnostics reagents were acting as a pseudo-gold standard, Siemens dRVVT detected 56/59, (95%) Group 1 LA and HBM dRVVT 46/59, (76%), one each from Group 2, and Siemens dRVVT detected one in Group 5. The lower HBM dRVVT detection rate mainly concerned weaker LA, where between-reagent concordance is problematic. All Group 3 patients appeared LA-positive in undiluted plasma with Siemens dRVVT, as did 16/24 (67%) with HBM dRVVT but the fewer LA-positives in mixing tests better mapped to clear LA-positives with LD dRVVT. LD and Siemens dRVVTs exhibited 87% and 95% false-positivity for Group 6 whilst HBM dRVVT had none. Increasing the cut-off improved accuracy. Applying higher cut-offs improved accuracy in Group 4 patients. Conclusion HBM dRVVT exhibited improved specificity, mainly due to less interference by anticoagulation, but reduced sensitivity, compared to the other dRVVTs employed.

Introduction A prolonged activated partial thromboplastin time (APTT) may be indicative of a specific or multiple factor deficiency, therapeutic anticoagulation, presence of a nonspecific factor inhibitor, or lupus anticoagulant (LA). Recently, pairing of the LA‐sensitive APTT and standard APTT reagents, Cephen LS and Cephen, respectively, has been shown to be effective in LA detection. The present study aimed to evaluate the usefulness of this reagent pair for discriminating between causes of APTT elevation and the detection of LA in conjunction with dilute Russell's viper venom time (dRVVT). Methods Plasma samples from 50 normal and 105 non‐anticoagulated LA‐positive patients in routine dRVVT and/or dilute APTT (dAPTT) via the percent correction formula were employed. Cephen LS/Cephen and dRVVT reagents LA1/LA2 were used to screen/confirm, respectively. Thirty‐four symptomatic LA‐negative, 25 warfarinised non‐antiphospholipid syndrome, 6 coagulation inhibitors, 17 samples with hereditary elevated APTT, and 24 FVIII/IX/XI/XII and 17 FII/V/X artificial single deficiency plasmas were used. Results Thirty‐three samples out of 105 (31%) were LA‐positive in Cephen LS/Cephen. The total percent positivity in Cephen LS/Cephen and LA1/LA2 pairs was 89.1% against samples with the routine dRVVT/dAPTT double positive. The percent corrections of Cephen LS/Cephen in the routine dAPTT/dRVVT positive group were significantly higher than those in all other groups. Conclusions The percent correction of the APTT reagent pair showed higher values in LA‐positive samples. The combination will be useful with respect to differentiating LA from other abnormal samples and is effective in LA detection when paired with dRVVT.

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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.