Serum and red cell ferritin content in the evaluation of iron status in rheumatoid arthritis.

We measured the basic (spleen type) ferritin content in the serum and red cells of 72 patients with rheumatoid arthritis in order to evaluate their significance in detecting true iron deficiency that may coexist with an altered metabolism of iron. Sixteen patients had no anaemia, and their serum and red cell ferritin contents were within the normal range (serum ferritin 16 to 286 micrograms/l; red cell ferritin, 5 to 44 ag/cell). Twenty patients had normocytic normochromic anaemia, and 36 patients had microcytic hypochromic anaemia. In these anaemic patients, the serum ferritin level ranged from 0 to 12 micrograms/l in 4, 13 to 55 micrograms/l in 19, 56 to 110 micrograms/l in 16, and exceeded 110 micrograms/l in 17 patients. The red cell ferritin content was subnormal (less than 5 ag/cell) in 4/20 patients in the normocytic normochromic group, and in 15/36 patients in the microcytic hypochromic group. Oral iron therapy given for 4-6 weeks to 9 patients with subnormal red cell ferritin resulted in an increase in the haemoglobin concentration; no such response was observed in patients with normal red cell ferritin content, irrespective of the serum ferritin concentrations. These observations indicate that red cell ferritin content is a more reliable index of true iron deficiency than serum ferritin concentrations in rheumatoid arthritis, and is capable of predicting the response to iron therapy.