Serum ferritin as a serologic marker of activity in systemic lupus erythematosus.

To investigate the relationship between serum ferritin and disease activity in systemic lupus erythematosus (SLE), we enrolled 128 patients with SLE (18 males and 110 females). Twenty-eight patients (2 males and 26 females) with rheumatoid arthritis (RA) served as controls. The SLE patients were subdivided into three groups according to Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) scores: groups A (0-5), B (6-9), and C (> or =10). We prospectively evaluated 48 SLE patients before and after treatment. Serum ferritin and anti-dsDNA antibody were measured by radioimmunometric assay. C-reactive protein (CRP) was measured quantitatively by immunonephelometry. Complements 3 and 4 (C3 and C4) were measured by nephelometry. Serum levels of ferritin during the more active stage of SLE (group C) exceeded those of RA patients and patients at less active stages of SLE (groups A and B). There were no significant differences between RA patients and groups A and B. Serum ferritin was elevated especially in serositis and hematologic manifestation. In this prospective study, changes in SLEDAI scores before and after treatment correlated significantly with serum ferritin levels and inversely to C3 and C4 levels. We confirm that serum ferritin levels can be a useful marker of disease activity in SLE patients.