A new-generation dilute Russell's viper venom time assay system for lupus anticoagulants: evaluation of detection utilising frozen reagents and controls.

The dilute Russell's viper venom time (DRVVT) is one of the most widely used assays to detect lupus anticoagulants (LAs). Variation in diagnostic performance exists between DRVVT reagents from various manufacturers due to a variety of factors such as antibody heterogeneity, reagent phospholipid composition, venom heterogeneity, assay methodology and analytical technique. Recently, a new-generation DRVVT assay system has become available that utilises frozen reagents and controls that offer potential benefits to the diagnostic laboratory in terms of reagent quality and convenience of use. This study evaluates the diagnostic and analytical performance of these CryoCheck reagents and controls on a commonly employed automated coagulation analyser, the Sysmex CA 1500. Sensitivity is assessed by analysis of 60 samples shown to contain LAs by combinations of an alternative DRVVT, LA-sensitive dilute activated partial thromboplastin time and activated seven lupus anticoagulant assay. Specificity is assessed using 30 samples negative for LA, eight plasmas from non-LA orally anticoagulated patients and also immunodepleted factor-deficient plasmas. The CryoCheck reagents generated comparable diagnostic performance data to that previously reported for other reagents. There was a marked improvement in sensitivity when the BCSH recommended percent correction of ratio calculation for assessment of phospholipid dependence was employed in place of the manufacturer suggested test/confirm ratio. Slightly better diagnostic performance was achieved when using a frozen pooled normal control in place of a lyophilised normal control to generate sample/control ratios, giving sensitivity, specificity, positive predictive and negative predictive values of 88.2%, 86.8%, 90% and 85.2%, respectively. The combination of CryoCheck reagents and the Sysmex CA 1500 analyser provides a sensitive and specific LA detection technique comparable to those currently available.