Diagnostic accuracy of silica clotting time method for lupus anticoagulant in a clinical population with various symptoms of antiphospholipid syndrome

Abstract

Introduction: Correct interpretation of lupus anticoagulant (LA) tests is crucial for diagnosis of antiphospholipid syndrome (APS). This study assessed diagnostic accuracy of the SCT method in a clinical population with various symptoms of APS. Material and methods: Altogether 60 APS patients were consecutively recruited from a relevant clinical population. All cases had stable positivity of at least one of the reference tests (two other LA methods; anticardiolipin- and anti-β2-glycoprotein-I antibodies). Controls (n = 62) with negative reference tests were also consecutively recruited from the same clinical population. Results and conclusions: Receiver operator characteristic (ROC) analysis for the SCT test to identify the APS cases showed area under the curve of 0.82 (95% CI 0.75–0.90). The positive cut-off defined by a non-parametric method (99 percentile in a healthy population) had specificity of 92%, but low sensitivity of 53%. The optimal cut-off corresponded to the 97.5 percentile (67% sensitivity and 92% specificity). Combined sensitivity of the positive diluted Russell Viper Venom time (dRVVT) and SCT tests was 73%, while specificity remained 92%. The sensitivity of the SCT method varied in different clinical subgroups and was highest in patients with rheumatic diseases and in patients with triple positivity of three reference methods.