Testing for lupus anticoagulants--fresh or frozen?

ABSTRACT

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)/µL (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/µL (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.