Testing for lupus anticoagulants - Fresh or frozen?

Background: There are no previous studies reporting the effect of using frozen-thawed plasma on lupus anticoagulant ratios in kits with the combined screen and confirm assay. Methods: In the following study we chose patients with elevated dilute Russel's viper venom test (dRVVT) normalized ratios and compared the test results of fresh to frozen-thawed plasma. Platelet counts ranged from 2 to 7 × 10 3/μ L (10 9/L) after a second centrifugation before freezing. Results: There were 13 out of 14 dRVVT test normalized ratios that decreased after freezing (p < 0.001), leading to the misclassification of six of 14 patients with high values that decreased into the reference interval. Conclusion: The major finding of this study is that testing frozen-thawed plasma with platelet counts < 10,000/μ L (10 9/L) results in a significant decrease in dRVVT ratios. Although there was a consistent decrease in SCT normalized ratios as well, it did not lead to misclassifications.