Determination of Ig M to b2-glycoprotein I in blood serum by indirect immunofluorescence

β2-glycoprotein I IgM is designed to quantify in vitro IgM antibodies directed at β2-glycoprotein I in human serum and plasma, to assist in the diagnosis of antiphospholipid syndrome (APS) and to assess the risk of thrombotic complications in patients with systemic lupus erythematosus (SLE).

Antiphospholipid syndrome (APS), also known as "Hughes syndrome", is characterized by typical clinical signs such as arterial/venous thrombosis or miscarriage, as well as persistently positive tests for antiphospholipid antibodies.

The APS classification criteria were revised in 2004 in Sydney. In addition to the clinical criteria, three different laboratory tests are listed: anticoagulant lupus, antibodies against cardiolipin (IgG and IgM) and antibodies against β2-glycoprotein I (IgG and IgM). The latter was not included in the Sapporo criteria. However, by a majority, the Sydney Committee agreed that they are an independent risk factor for thrombosis and pregnancy complications.

For the diagnosis of APS, tests for antibodies to β2-glycoprotein I show higher specificity than tests for anticardiolipin. In 3-10% of patients with APS, antibodies against β2-glycoprotein I may be the only positive test. The association of antibodies to β2-glycoprotein I with preeclampsia and/or eclampsia in pregnant women who tested negative for antibodies to anticardiolipin suggests that the inclusion of antibodies against β2-glycoprotein I may also help clarify this type of morbidity during pregnancy. Outside the context of clinical analysis, testing for antibodies to β2-glycoprotein I may be useful for the diagnosis of APS, especially when nticardiolipin antibodies and an anticoagulant for lupus are negative and APS is suspected.