denotes an abstract that is clinically relevant.
denotes that this is a recommended PHD Trainee Session.
denotes that this is a ticketed session.Session: 301. Vasculature, Endothelium, Thrombosis and Platelets: Basic and Translational: Poster I
Hematology Disease Topics & Pathways:
Research, Bleeding and Clotting, autoimmune disorders, Clinical Research, Diseases, Immune Disorders, thrombotic disorders
Laboratory diagnosis of the antiphospholipid antibody syndrome (APS) requires evidence of persistently positive lupus anticoagulant (LAC) activity in clot-based assays and/or the presence of medium-high titer anticardiolipin (aCL) and/or anti-beta 2 glycoprotein I (aB2GPI) antibodies. Although aCL and aB2GPI methodologies provide quantitative information about the antibody titer, LAC testing is interpreted in a qualitative fashion (presence versus absence).
Objectives
In this study, we describe a method for measuring the LAC titer and evaluate the relationship between the LAC titer, other antiphospholipid antibodies and clinical outcomes.
Methods
Residual plasma from 51 LAC-positive samples (50 unique patients) were included in this study. To estimate LAC-titers, samples were tested undiluted and subjected to serial (dependent) twofold dilutions in pooled normal plasma (PrecisionBiologic) up to a final dilution of 1:128, as appropriate. The dilute Russell’s viper venom screening time (DRVVT screen, LA Check, PrecisionBiologic) and activated partial thromboplastin screening time (APTT, SynthasIL, Werfen) were measured for each dilution. A four-parameter logistic model of the dilution factor versus the clotting time was used to interpolate the LAC-titer at the upper limit of normal for both assays (APTT of 37s and DRVVT screen ratio of 1.2). Measurements of aCL, aB2GPI and anti-phosphatidylserine/prothrombin antibodies (aPS/PT) were performed using ELISA methodologies (QUANTA Lite, Werfen). Available clinical data were extracted from the electronic medical record. Continuity corrected chi-square test was used as a categorical test of association and quantile regression was used to compare medians for interval/ratio data across subgroups (Stata v17).
Results
There was a strong positive linear relationship between the APTT and DRVVT titers (Pearson’s correlation coefficient, r=0.92, Figure 1A). There was only a moderate relationship between the APTT titer and the APTT screen in the undiluted sample (r=0.50) and almost no relationship between the DRVVT titer and the DRVVT screen ratio or DRVVT screen/confirm ratio in the undiluted sample (r=0.06 and r=0.13, respectively). Data-driven partitioning identified two DRVVT titer groups: low-titer (<10) and high-titer (≥10). Empirical cutpoint estimation (Youden) identified an APTT titer threshold of 5 for predicting the DRVVT titer group. Among patients with available clinical history, 15 of 25 (60%) low-DRVVT-titer and 16 of 20 (80%) high-DRVVT-titer patients had thromboembolic/obstetric events (p=0.26). Autoimmune diagnoses were more prevalent in the low-DRVVT-titer group (19 of 25 patients, 13 with SLE) than the high-DRVVT-titer group (8 of 20 patients, 3 with SLE, p=0.03). Comparing the low and high-DRVVT-titer groups, median aCL IgM (p=0.27), aCL IgG (p=0.99), aB2GPI IgM (p=0.72) and aB2GPI IgG (p=1.00) titers were not different. High-DRVVT-titer samples had a significantly higher median aPS/PT IgM compared to low-DRVVT-titer samples (p <0.01, Figure 1B) but there was no difference observed for IgG aPS/PT (p=0.57, Figure 1B).
Conclusions
APTT and DRVVT screening times are not strongly correlated with the corresponding APTT or DRVVT LAC-titer and may not indicate LAC potency. High DRVVT LAC-titers were strongly associated with IgM aPS/PT levels, but not with aCL, aB2GPI or IgG aPS/PT levels. Further research is required to evaluate the association between the LAC-titer and recurrent thrombosis in APS.
Disclosures: Pruthi: Instrumentation Laboratory: Honoraria, Membership on an entity's Board of Directors or advisory committees; HEMA Biologics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer Healthcare AG: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech Inc: Honoraria, Membership on an entity's Board of Directors or advisory committees; CSL Behring: Honoraria, Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy.