Utility of phospholipid-sensitive and insensitive APTT pairs together with dRVVT in the diagnosis of lupus anticoagulant

Introduction and objective: Laboratory diagnosis of antiphospholipid syndrome (APS) requires the determination of lupus anticoagulant (LA) activity by coagulation assays and antiphospholipid antibodies by solid-phase assays. Despite the years that have passed, the diagnosis of LA is still complex and requires well-established coagulation methods, properly obtained cut-off points and professional judgment for the interpretation of the results. Method: Two types of specific assays for LA based on different principles: dRVVT (dilute Russell’s viper venom time) and sensitive APTT are recommended for the detection of LA. This is complemented by mixing assays with normal plasma and confirmatory assays. One of the interpretations is based on the calculation of the detection assay/confirmatory assay ratio. In an attempt to resemble the dRVVT detection/confirmatory assay, various combinations have recently been proposed using APTT with low or high sensitivity to phospholipids. In two centres (one with optical coagulometer and another with mechanical detection) we used PTT-LA as sensitive APTT and Pathromtin-SL and CK-Prest as insensitive APTTs. Results: Based on locally established cut-off points, in centre A 50 patients were positive for AL out of 173 evaluated. In centre B there were 36 positives out of 130 patients. In both centres the combination of paired APTTs (sensitive/insensitive) PTT-LA/Pathromtin or PTT-LA/CK-Prest demonstrated high sensitivity to detect AL. Conclusions: This strategy proved to be useful and economical for the diagnosis of AL according to current international standards.