FRI0327 Reliability of la and diagnostic performance of aps/pt in different clinical settings of aps: a multicenter study
Authors: M. Radin, I. Cecchi, E. Rubini, A.M. Scotta, R. Rolla, B. Montaruli, P. Pergolini, G. Mengozzi, E. Muccini, D. Roccatello, S. Sciascia
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Correct interpretation of lupus anticoagulant (LA) tests is crucial for diagnosis of antiphospholipid syndrome (APS). However, testing patients during vitamin K antagonist (VKA) or other anticoagulant remains a contentious issue and has been discouraged by official guidelines<sup>1</sup> because of interpretational problems affecting the mixing test. Similarly, the clinical significance of weak LA, especially in the context of VKA, remains uncertain and certainly needs a more thorough evaluation. Autoantibodies that recognise a phosphatidylserine/prothrombin (PS/PT) complex have been reported to be associated with APSandmay have diagnostic relevance in these settings. <h3>Objectives</h3> To evaluate the reproducibility of LA testing when performed in different centres and to assess the diagnostic performance of anti-PS/PT in different clinical settings of APS. <h3>Methods</h3> aPL testing was performed in a blind fashion in 4 centres. LA was tested as per the current criteria from the ISTH Subcommittee on LA-Phospholipid-dependent antibodies.<sup>1</sup> Thirty-two patients were enrolled in this study, as follows: 13 patients with thrombotic APS treated with vitamin K antagonist; 5 patients thrombotic APS treated with DOAC; 14 patients with transitory/low aPL titer. Anti-PS/PT IgG/IgM (aPS/PT, Inova Diagnostics)were tested by ELISA. We analysed the categorical agreement and degree of linear association, for LA and aPS/PT, respectively. <h3>Results</h3> Demographic, clinical and laboratory characteristics are summarised in table 1. Categorical agreement for LA among the centres, as expressed by Cohen's <i>kappa</i> coefficients, ranged between 0.61 and 0.80 (as substantial agreement). The correlation among quantitative results in the aPS/PT IgG was strong (when dichotomizing for positive Vs. negative results, Cohen's <i>kappa</i> coefficients=0.81–1. Spearman rho 0.84). We observed 12 (37.5% of the total) cases (7/12,58%patients on VKA) in which LA results were discordant(as defined by lack of agreement in ≥2 laboratories) or inconclusive. Conversely, in those cases, we observed a good correlation for aPS/PT IgG testing (Cohen's <i>kappa</i> coefficients=0.81–1, Spearman rho 0.86). <h3>Conclusions</h3> Despite the progress in the standardisation of aPL testing, we observed up to 37.5% of discrepant results for LA, especially in patients on VKA. Our findings showed that some discordances in the reliability of LA testing still exist. The introduction of aPS/PT antibodies in the diagnostic process of APS might represent a further diagnostic tool, especially when LA is not available or nor reliable. <h3>Reference</h3> [1] Pengo V, et al. Update of the guidelines for lupus anticoagulant detection. Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibody of the Scientific and Standardisation Committee of the International Society on Thrombosis and Haemostasis. J Thromb Haemost2009;7:1737–40. <h3>Disclosure of Interest</h3> None declared