Measures IgA antibodies against beta‑2 glycoprotein I, a protein that binds phospholipids. Persistent antibodies can be linked to abnormal clotting, especially when other APS markers are positive.
Used (with other antiphospholipid antibody tests) when there are unexplained clots or pregnancy complications to assess possible antiphospholipid syndrome; IgA may be added in selected cases.