Relationship between serum ferritin, iron stores and disease activity in rheumatoid arthritis.

Bone marrow aspirate from the sternum of 40 patients with active or inactive rheumatoid arthritis (RA) was stained with Perls' Prussian blue for iron determination. In these patients serum ferritin concentrations were correlated with other indices of iron stores and disease activity. In patients with active RA and without bone marrow iron stores, serum ferritin was significantly lower than in patients with either active or inactive RA and iron stores. In patients with bone marrow iron stores, serum ferritin was directly correlated with erythrocyte sedimentation rate (ESR), Ritchie index, alpha 1-antitrypsin, alpha 1-acid glycoprotein and desferrioxamine (DFO)-induced sideruria, while an inverse correlation of serum ferritin with hemoglobin and serum iron was observed. In all patients serum ferritin was significantly correlated only with DFO-induced sideruria and unsaturated iron-binding capacity (UIBC). Thus, serum ferritin is an index of iron stores also in rheumatoid arthritis. In active disease, higher than expected values of serum ferritin are probably due to a shifting of iron from the circulating pool to the reticuloendothelial cells of the synovial membrane.