A normalized dRVVT ratio (LA screen/LA confirm) of > 1.2 was considered abnormal [4]. Mixing studies for lupus anticoagulant: mostly no, sometimes yes. Plasma was prepared by double centrifugation (2 × 1300 × g for 15 min) commenced no more than 2 h after blood had been collected. Lupus Anticoagulants, Antiphospholipid Antibodies, and Antiphospholipid Syndrome. The DRVVT may be abnormally prolonged (DRVVT screen ratio > or =1.20) by LA as well as coagulation factor deficiencies, anticoagulant effects, or other types of coagulation factor inhibitors. The venom contains the enzymes RVV-V and RVV-X which activate factor V and factor X, which converts prothrombin into thrombin in the presence of phospholipid and calcium. Current practices for lupus anticoagulant testing at a tertiary care hospital and impact on laboratory resources. †Each of these patients was also found to have antiphospholipid antibodies. Interpretation of normal plasma mixing studies in the laboratory diagnosis of lupus anticoagulants. The dilution effect of equal volume mixing studies compromises confirmation of inhibition by lupus anticoagulants even when mixture specific reference ranges are applied. APTT, Activated partial thromboplastin time; LA, lupus anticoagulant; OAC, oral anticoagulants. The final product had a platelet count of < 5 × 109, a factor VIII of > 80% and normal APTT and dilute Russell viper venom time (dRVVT). In patients with a coagulation factor deficiency, a prolonged clotting time is readily corrected by the addition of a small volume of normal plasma while relatively large volumes of plasma are required to correct the clotting time in patients with LA [2]. With a reflexive testing algorithm, the sensitivity of DRVVT testing for LA diagnosis is approximately 65% to 70% and the … This in vitro diagnostic test is based on the ability of the venom of the Russelli viper to accelerate blood clotting. International Journal of Laboratory Hematology. Performance of dilute Russell viper venom test and silica clotting time in comparison with Staclot LA, The importance of locally derived reference ranges and standardized calculation of dilute Russell's viper venom time results in screening for lupus anticoagulant. Lupus anticoagulant mixing tests for multiple reagents are more sensitive if interpreted with a mixing test‐specific cut‐off than index of circulating anticoagulant. Guidelines on the investigation and management of antiphospholipid syndrome. Evaluation of the phospholipid-rich dilute Russell's viper venom assay to monitor oral anticoagulation in patients with lupus anticoagulant. Current Controversies in Lupus Anticoagulant Detection. Blood samples were collected from patients and healthy donors into vacuum tubes containing 1/10 volume 0.109 m trisodium citrate (Becton Dickinson, Franklin Lakes, NJ, USA). The full text of this article hosted at iucr.org is unavailable due to technical difficulties. However, only one of the three patients with an abnormal dRVVT ratio after 50/50 mixing also had a long APTT after mixing. Please check your email for instructions on resetting your password. However, mixing studies dilute the concentration of the LA antibody, which could potentially lead to false‐negative results if the antibody is weak. Patients with LA were recruited from among consecutive patients investigated for an unexplained prolonged activated partial thromboplastin time (APTT) or referred to the thrombosis clinic for advice regarding the management of venous or arterial thrombosis, thrombocytopenia or unexplained miscarriage. Our study results highlight the limitations of mixing studies and suggest that normal plasma correction of an abnormal screening test should not necessarily preclude further laboratory evaluation for the diagnosis of LA. Learn more. A long APTT and abnormal dRVVT ratio were found in 70.5% and 41.1%, respectively, of patients on OAC who did not have a known LA. Use the link below to share a full-text version of this article with your friends and colleagues. Specimens with abnormal results (DRVVT screen ratio ≥1.20) are subjected to reflexive testing. Clinical Chemistry and Laboratory Medicine. Mixing studies were performed using a 50/50 mix of patient and normal plasma and these were deemed to have corrected if the result of the mix fell within the normal range (APTT 29.5–40.0 s, dRVVT ratio < 1.2). Specimens with abnormal results (DRVVT screen ratio > or =1.20) are subjected to reflexive testing. Only about 50% of LA‐positive patients had a prolonged APTT after mixing. The laboratory diagnosis of lupus anticoagulant in patients on oral anticoagulation. veritas? The International Society on Thrombosis and Haemostasis (ISTH) Scientific Subcommittee criteria for the laboratory diagnosis of lupus anticoagulant (LA) suggest that at least two methods, one with low phospholipid concentration, be used to screen for the antibody and a confirmatory test should demonstrate its phospholipid dependence. This may be a particular problem in patients taking oral anticoagulants (OAC) because 50/50 mixing with normal plasma is widely used in these patients prior to testing for LA to bring clotting times into the range of the assay technique [3]. The results of LA testing are summarized in Table 1. These were correctable in the majority of cases by 50/50 normal plasma mixing studies. Laboratory diagnostic outcome applying detection criteria recommended by the Scientific and Standardization Committee of the ISTH on Lupus Anticoagulant. The DRVVT may be abnormally prolonged (DRVVT Screen Ratio > or =1.20) by LA as well as coagulation factor deficiencies, anticoagulant effects, or other types of coagulation factor inhibitors. Patients with liver disease, known coagulation factor deficiencies, or receiving other anticoagulants were excluded. Demonstration of the presence of an inhibitor is considered an essential criterion for the diagnosis of LA [1, 2]. These patients either had a contraindication to anticoagulation or subsequently started warfarin. Of the 17 LA‐positive patients not anticoagulated, four had arterial thrombosis (one small, three large vessel) and one had venous thrombosis. Specimens with abnormal results (DRVVT screen ratio > or =1.20) are subjected to reflexive testing (see Testing Algorithm). Clinical Chemistry and Laboratory Medicine (CCLM). Learn about our remote access options, Department of Haematology, Royal Perth Hospital, Perth, Australia. Number of times cited according to CrossRef: To Mix with Pooled Normal Plasma or Not to Mix: A Comparative Study of 2 Approaches for Assessing Lupus Anticoagulant Inhibitory Activity in the Dilute Russell Viper Venom Method. Lupus anticoagulant testing – sometimes mixing is required. Of the 12 patients with LA stabilized on OAC, six had venous thromboembolism (VTE), two had arterial thrombosis and four had a valve replacement of whom one also had cancer. By contrast, when the prevalence of LA in the population being tested is low, failure to use mixing studies when testing for LA in patients taking OAC can lead to false‐positive results in as many as one‐third of patients (poor positive predictive value). and you may need to create a new Wiley Online Library account. With a reflexive testing algorithm, the sensitivity of DRVVT testing for LA diagnosis is approximately 65% to 70% and … Criteria for the diagnosis of lupus anticoagulants: an update. ECAT With the reflexive testing algorithm, the sensitivity of DRVVT testing for LA diagnosis is … . These results indicate that mixing studies with normal plasma in patients undergoing laboratory testing for LA may yield conflicting results, with improvements in specificity being achieved at the cost of reduced sensitivity. Testing for LA was performed using standard laboratory methods. Evaluating laboratory approaches to the identification of lupus anticoagulants: A diagnostic challenge from the RCPA Haematology QAP. Screening studies included an APTT (Platelin LS; Organon Teknika, Durham, NC, USA) and dRVVT (LA Screen; Gradipore, Frenchs Forest, NSW, Australia).