Clinical significance of anti-domain 1 β2-glycoprotein I antibodies in antiphospholipid syndrome.

BACKGROUND: Antiphospholipid syndrome (APS) is characterized by the presence of circulating antiphospholipid antibodies (aPL) in patients with thrombosis and/or pregnancy morbidity. In APS patients anti-domain 1 β2-glycoprotein I (anti-D1 β2GPI) IgG antibodies correlate strongly with thrombosis and to the lesser extent, with pregnancy complications. The aim of this study was to assess clinical utility of the anti-D1 β2GPI antibodies in the diagnosis and risk stratification of antiphospholipid syndrome. PATIENTS/
METHODS: In this retrospective study 202 autoimmune patients were studied (primary APS - 58, secondary - 45 SLE - 99). Anticardiolipin (aCL) and anti-β2GPI (aβ2GPI antibodies) (IgG and IgM class) together with anti-D1 IgG were tested with QUANTA Flash chemiluminescent immunoassay and lupus anticoagulant (LA) with coagulometric methods.
RESULTS: The highest anti-D1 values were observed in triple positive patients as compared to patients with other antiphospholipid antibody profiles. A strong correlation was found between levels of anti-D1 IgG and a β2GPI IgG antibodies for all patients analyzed (Spearman's ρ=0.87; p<0.0001). Anti-D1 IgG antibodies increase specificity resulting from classic aPL positivity but at the expense of sensitivity. Anti-D1 test does not add accuracy in predicting APS thrombotic complications on the top of accuracy offered by classic aPL tests and their profiles.
CONCLUSIONS: Anti-D1 IgG antibodies did not add diagnostic power to the standard laboratory aPL tests as assessed by this retrospective study. A true clinical significance of anti-D1 antibodies in thrombotic risk stratification of aPL positive patients will require a properly designed clinical prospective trials.