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The antiphospholipid antibody syndrome (APS) is defined as the occurrence of arterial or venous thrombosis or fetal loss, in association with persistently positive immunoassays for IgG or IgM anticardiolipin antibody (ACA), or coagulation tests for lupus anticoagulant. The APS may be associated with autoimmune disorders, especially SLE (secondary APS) or may occur independently (primary APS). Positivity for anti-beta-2-glycoprotein I (anti-B2GPI) has been shown to be more closely associated with clinical manifestations of APS, including thrombosis, than the ACA assays. An immunoassay for anti-B2GPI has been available at Saint Luke's Regional Laboratories since 1998, and is a component of our "Antiphospholipid III" panel, which includes coagulation tests for lupus anticoagulant and immunoassays for ACA (IgG and IgM). The anti-B2GPI assay currently being performed will detect only the IgG isotype of the antibody. Recently an immunoassay for the IgM isotype of anti-B2GPI has become available. A recent study evaluated a number of different antiphospholipid antibodies (including both IgG and IgM anti-B2GPI) as predictors of thrombosis, in 100 patients with primary APS, and 90 patients with SLE, 40 of whom had secondary APS. In the patients with SLE, both IgG and IgM anti-B2GPI were strongly associated with the clinical manifestations of APS, with specificity greater than 95%, and positive predictive values (PPV) greater than 90%. In the patients with primary APS, both IgG and IgM anti-B2GPI were strong predictors of thrombosis, especially arterial thrombosis (PPV greater than 90% for both antibodies). The presence of anti-B2GPI antibody has not yet been included in the formal definition of APS, but may be in the future. In any event, detection of IgG or IgM anti-B2GPI would add credence to a diagnosis of APS, especially in borderline cases. Assay for IgM anti-B2GPI will be available in Saint Luke's Regional Laboratories starting in March 2005. Both IgG and IgM anti-B2GPI will be performed when anti-B2GPI is ordered. IgM anti-B2GPI will also be added to all panels in which IgG anti-B2GPI is already a component (this includes the Antiphospholipid III panel and venous thrombosis panel). Reference range for both IgG and IgM anti-B2GPI is 0-20 units. Sample requirement for anti-B2GPI is one red-top tube (minimum 1.0 ml serum). |
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