Anti beta 2 Glycoprotein 1 Screen

The antiphospholipid syndrome (APS) is a disorder that
presents peculiar symptoms: arterial and venous
thrombosis, thrombocytopenia, ulcers of the lower limbs,
hemolytic anemia, loss of the fetus during pregnancy and
is associated with the presence of antiphospholipid
antibodies. Antiphospholipid antibodies represent a large
and heterogeneous immunoglobulins group, including
anticardiolipin antibodies and lupus anticoagulant. The
former are diagnosed by on their reactivity with cardiolipin
or other anionic phospholipids in ELISA test, while the
latter is detected in phospholipid-dependent coagulation
tests (aPTT, KCT, dRVVT).
In early '90s it was observed that antiphospholipid
antibodies are not directed against anionic phospholipids,
as long it was considered, but they react with plasma
proteins bound to anionic (phospholipidic) surfaces. In fact
about cardiolipin, it was observed the need of a cofactor for
antibodies binding, this cofactor was identified in β2
glycoprotein 1 (β2-GP1). The β2 glycoprotein 1 is a plasma
glycoprotein of molecular weight of 50 kD, which is
complexed to lipoproteins for 40%. A patient with clinical
suspicion of APS, who has an high titre of anti-beta2GP1
antibodies, even if LAC or anti-cardiolipin antibodies are
negative, has a strong chance of having the
antiphospholipid syndrome, because these antibodies
recognize β2-GP1 bound to the surface of phospholipid
(cardiolipin). These proteins seem to express their
antigenicity only after contact with specific areas such as
the anionic phospholipid surface or very hydrophilic plastic
surfaces.
The importance of ELISA anti-phospholipids test, including
the anti-β2-GP1 test, lies in the fact that a positive test if
associated with one or more of the symptoms can confirm
a diagnosis of APS.