title: Antiphospholipid antibody syndrome: the flow cytometric annexin A5 competition assay as a diagnostic tool.
abstract: The mechanism underlying hypercoagulability in antiphospholipid antibody syndrome (APS) is uncertain. Here, we present a flow-cytometric assay (FCA) based on the hypothesis that anti-platelet-anionic-phospholipid autoantibodies (aPL) interfere with the activity of the natural anticoagulant protein annexin A5, thereby accelerating platelet procoagulant activity. This study assessed the clinical utility of the feasible FCA, which demonstrates the competition of the patient's aPL with the binding of annexin A5 to the platelet-anionic-phospholipids, in the diagnosis of APS. Sixty-two (94%) of 66 APS patients, 20 (51%) of 39 patients with systemic lupus erythematosus and two (4%) of 49 healthy individuals were positive by FCA. Compared with the anticardiolipin (aCL) assay, the relative sensitivity was 82% and the specificity 73.3%. However, 19 (25%) aCL-negative patients were positive by FCA; 12 were positive for lupus-anticoagulant (LA). Compared with LA assay, the relative sensitivity was 85% and the specificity 72.2%. However, 21 (26%) LA-negative patients were FCA-positive, 12 were positive for aCL. The FCA was particularly sensitive for APS patients with arterial (97.0%) and gestational vascular complications (100%) with overall sensitivity of 95% and specificity of 97%. Our findings suggest that the FCA is practical, sensitive and specific for the detection of clinically relevant aPL in the diagnosis of APS.
authors.affiliation: Blood Bank and Transfusion Medicine, Soroka University Medical Centre, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel. atomer@bgu.ac.il
authors.forename: A
authors.initials: A
authors.lastname: Tomer
authors.forename: S
authors.initials: S
authors.lastname: Bar-Lev
authors.forename: S
authors.initials: S
authors.lastname: Fleisher
authors.forename: B
authors.initials: B
authors.lastname: Shenkman
authors.forename: M
authors.initials: M
authors.lastname: Friger
authors.forename: M
authors.initials: M
authors.lastname: Abu-Shakra
mesh_terms: D000328:Adult; D017304:Annexin A5 / Q000378:metabolism; D017153:Antibodies, Anticardiolipin / Q000097:blood; D016736:Antiphospholipid Syndrome / Q000175:diagnosis* / Q000378:metabolism; D019540:Area Under Curve; D001780:Blood Coagulation Tests; D001792:Blood Platelets / Q000378:metabolism; D016022:Case-Control Studies; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000032:analysis; D008297:Male; D008875:Middle Aged; D015539:Platelet Activation; D011247:Pregnancy; D011485:Protein Binding; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D017304:Annexin A5; D017153:Antibodies, Anticardiolipin; D016682:Lupus Coagulation Inhibitor