Background Antiphospholipid antibodies in SLE may be affected by disease activity and treatment, but past studies have been conflicting. We investigated the association of titers of antiphospholipid antibodies with disease activity and therapy.

Methods 943 SLE patients, who had at least 10 quarterly visits for testing for each anticardiolipin isotype (IgG, IgM and IgA) and dRVVT, were included in the study. Disease activity was measured with both the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) and Physician Global Assessment (PGA). Treatment was recorded at every visit.

Results aCL IgG >40 and aCL IgA were not associated with disease activity. Hydroxychloroquine reduced the levels of all antibodies, except for IgA aCL. Prednisone reduced aCL IgG but not aCL IgM, aCL IgA >40 or dRVVT (seconds prolongation).

Conclusion High titer aCL were not affected by disease activity. Thus these patients are more like ‘primary’ antiphospholipid patients. Hydroxychloroquine use was associated with reduced lupus anticoagulant (by seconds of prolongation) and reduced titers for most of the isotypes of anticardiolipin. Prednisone did not reduce the seconds of dRVVT prolongation. Anticardiolipin IgA seemed the most resistant to therapy.