Comparison of laboratory tests used for identification of the lupus anticoagulant

A comparison of the sensitivities of the ten most commonly used tests for the identification of the lupus anticoagulant (LA) and the lupus cofactor phenomenon was undertaken on 18 patients. All investigations, except the cardiolipin‐antibody ELISA assay, were carried out using patient's plasma alone followed by a 1:1 mix with control plasma. Dilution studies (1:3, 1:6, 1:9—patient:control) were also carried out. The kaolin clotting time (KCT) was the only test positive in all patients at all dilutions, while the dilute activated partial thromboplastin time with kaolin (Dil‐APTT) registered 17 of 18 positive at all dilutions. Both the dilute Russell viper venom time (Dil‐RVVT) and the tissue thromboplastin inhibition time (TTI) (1/500 thromboplastin) identified the LA in 17 of 18 patients on initial testing but were less sensitive in the dilution studies. The KCT is not a suitable test for routine laboratory use, as it requires an individual filtration step. Therefore a combination of either the Dil‐APTT or Dil‐RVVT together with the TTI (1/500 dilution thromboplastin) is recommended for routine LA screening, as all patients with LA in this study were identified using these easily automated tests. The lupus cofactor phenomenon was most frequently demonstrated using the Dil‐APTT.