β₂-Glycoprotein 1 Antibodies, IgA, IgG, IgM

Serum

1 mL

0.5 mL

Red-top tube or gel-barrier tube

Assess the risk of thrombosis in patients who may be at risk for antiphospholipid syndrome (APS). This test should be used in conjunction with current traditional anticardiolipin and anticoagulant tests.¹

Anti-β₂-glycoprotein 1 should not be used alone as a screening test for antiphospholipid syndrome.

Enzyme-linked immunosorbent assay (ELISA) to detect antibodies binding to a microtiter plate coated with purified β₂-glycoprotein 1 antigen

• IgA = 0−25 GP1 IgA units

• IgM = 0−32 GP1 IgM units

• IgG = 0−20 GP1 IgG units

Recently, an international consensus group of experts in the diagnosis and management of antiphospholipid syndrome (APS) concluded that β₂-GP1 IgG and IgM antibodies should be included as diagnostic criteria for APS.² This group determined that the presence of one or both of these antibodies is an independent risk factor for thrombosis and pregnancy complications.³

A common aspect to all assays for anticardiolipin antibodies (ACA) is the requirement that the assay system include a source of plasma proteins.³ It has been determined that, in many patients, β₂-glycoprotein 1 (β₂-GP1) is the plasma factor required for ACA binding.^3,4 Solid-phase enzyme immunoassays that detect antibodies that bind to β₂-GP1 in the absence of phospholipid are now part of the diagnostic arsenal for APS. β₂-GP1-dependent binding is frequently detected in patients with clinical symptoms of APS.³ All three isotypes of anti-β₂-GP1 (IgG, IgM, and IgA) have been associated with thrombosis.^3,5,6 ACA that do not require β₂-GP1 are usually transient and not clinically significant. Studies have shown that ACA associated with infections tend to not be β₂-GP1-dependent.⁴ This supports the conclusion that anti-β₂-GP1 assays may be more specific for APS than ACA.^4,7,8 While the majority of patients with LA will also test positive for ACA and β₂-GP1 antibodies, approximately 30% of patients tested will have discordant results.^9,10 Approximately 20% of patients who test negative for ACA will test positive for β₂-GP1.⁹ Anti-β₂-GP1 testing can be useful in the evaluation of patients with positive ACA results and a clinical picture that is not consistent with APS.^3,4,8 A negative anti-β₂-GP1 result in this context would not support a diagnosis of APS. Anti-β₂-GP1 testing can also support the diagnosis of APS in patients with a strong clinical picture for APS with negative LA and ACA results.⁸