Laboratory tests - anti-beta-2 glycoprotein antibody

What it is

Anti-beta-2 glycoprotein I antibody - one of the three antiphospholipid antibodies tested in the diagnostic criteria for antiphospholipid syndrome (APS), alongside anticardiolipin antibody and lupus anticoagulant
Tested whenever APS is suspected - unexplained thrombosis (arterial or venous), recurrent pregnancy loss, or as part of the workup for SLE (given the substantial overlap between SLE and secondary APS)

Beta-2 glycoprotein I is a plasma protein that binds phospholipid surfaces; antibodies against it (rather than against phospholipid directly) are now understood to be the clinically relevant pathogenic target in most antiphospholipid-mediated thrombosis, promoting a prothrombotic state via several proposed mechanisms (endothelial activation, complement activation, interference with natural anticoagulant pathways)

Requires IgG or IgM antibody, at moderate-high titre, on two occasions at least 12 weeks apart - a single positive result is insufficient for diagnosis given the possibility of a transient, clinically insignificant positive (e.g. post-infection)
Used alongside anticardiolipin antibody and lupus anticoagulant testing - a patient may be positive for one, two, or all three, and "triple positivity" carries the highest thrombotic risk of any antiphospholipid antibody combination

Confirmed APS (clinical event + persistent antibody positivity) -> long-term anticoagulation (typically warfarin, not a DOAC, given evidence of inferior efficacy with DOACs specifically in APS) for thrombotic APS; low-dose aspirin +/- heparin for obstetric APS during pregnancy
Asymptomatic antibody positivity without a qualifying clinical event does not by itself warrant anticoagulation, though risk-factor modification and vigilance are appropriate

Antiphospholipid syndrome, SLE (secondary APS), recurrent pregnancy loss, arterial and venous thrombosis at an unusual site or young age

Diagnosis of APS requires BOTH a qualifying clinical event (thrombosis or defined pregnancy morbidity) AND persistent antibody positivity on repeat testing - neither alone is sufficient, a frequently tested distinction from simply having a positive antibody test

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.