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Conference Proceeding

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International Journal of Laboratory Hematology


Introduction: Lupus anticoagulants (LA) are antibodies directed against phospholipids/phospholipid-protein complexes involved in coagulation and are associated with thrombotic events and recurrent fetal loss. There is no gold standard test for LA, therefore at least two LA-specific tests are recommended before excluding LA. Potential testing methods involve dilute Russell viper venom time (dRVVT) and hexagonal phase phospholipid assays (HPPA); however, many of these tests are susceptible to interference with anticoagulant therapy which can lead to false positive results. In this study, we compared the performance of our current HPPA, StaClot LA (SCLA), with a novel assay reported to have relatively minimal interference by anticoagulation therapy, CRYOcheck Hex LA (CCLA).

Methods: We performed a retrospective study using 47 samples submitted for lupus anticoagulant testing in 3.2% sodium citrate vacutainer tubes. Samples were spun for 15 min at 3400 rpm to obtain platelet poor plasma. Samples positive by SCLA were selected for further testing and chart review for diagnosis of LA. These samples were frozen and retested by CCLA. We calculated the positive predictive value of both tests, assessed agreement between test methods using kappa statistics, and estimated the extent to which positive results were affected by anticoagulant therapy using Fisher's exact test. Statistical analysis was performed on R (version 4.2.1). Statistical significance was defined as p < 0.05.

Results: Of the 47 samples, 34 were from women and 13 were from men, with an average age of 56 years. Using ISTH criteria, the presence or absence of LA was able to be determined in 42 out of the 47 samples. A 15 samples were positive for LA, and 27 samples were negative. Of the 15 positive samples, all were detected by both SCLA and CCLA. Of the 27 negative samples, all were positive by SCLA, and one was positive by CCLA. Thus, the positive predictive value for SCLA was 35.7% and 93.8% for CCLA. Since positive and negative results were obtained with CCLA, we were able to assess overall agreement between CCLA and true LA patients and CCLA and dRVVT, both of which were good (kappa = 0.78, p < 0.0001 for true LA; kappa = 0.73, p < 0.0001 for dRVVT). Additionally, 21 patients were taking anticoagulants at the time their sample was drawn. The rate of anticoagulation therapy was significantly higher in SCLA samples with false positive results (61.5% in false positive vs. 14.3% in true positive; p = 0.007). Conclusions: Diagnosis of LA can be challenging, particularly when the patient is being treated with anticoagulation. In our study, hexagonal phase phospholipid assays (SCLA and CCLA) showed high sensitivity (100%); however, SCLA showed a significant false positive rate, largely due to patients on anticoagulation therapy. CCLA on the other hand, shows promising resistance to anticoagulant therapy, and therefore, should be a strong consideration for labs offering LA testing in patient populations that are frequently anticoagulated.

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ISLH International Symposium on Technological Innovations in Laboratory Hematology, May 12, 2023, New Orleans, Louisiana