Lupus anticoagulant testing: Analyzing fresh samples after a single centrifugation and after a 68 h delay

Background: For automation it is important to know the effect of analyzing fresh samples after a single rather than after two centrifugations, and to determine test stability. Methods: This study compared silica clotting times (SCT) and dilute Russel's viper venom tests (dRVVT) after one and two centrifugations in 50 fresh plasma samples. Then it compared test results within 4 h to those after 68 h of blood drawing in 40 samples. Means, minimums, maximums and quartiles of the paired screen were compared, test ratios were confirmed and correlations, linear regressions and Bland-Altman statistics were calculated. Results: The distributions of test results were nearly identical, regardless of the number of centrifugations or timing of the analysis. The first centrifugation explained 97.7 and 94.8 of the variance of tests results after the second centrifugation for the SCT and dRVVT, respectively. The test results after 68 h explained 98.3 and 96.3 of the variance of the SCT-ratios and dRVVT-ratios, respectively, tested within 4 h. Inter-day coefficients of correlation of ratio comparisons were similar to those of the controls values. Conclusions: Testing of fresh samples after a single centrifugation might replace batch testing of frozen samples after double centrifugation, providing timelier reporting of results and resulting in savings of technician time.