red cell ferritin content a reevaluation of indices for iron deficiency in the anaemia of rheumatoid arthritis in iron deficiency anaemia basic red cell content of ferritin is appreciably reduced this variable was determined in 62 patients with rheumatoid arthritis to evaluate conventional laboratory indices for iron deficiency in the anaemia of rheumatoid arthritis for 23 patients with rheumatoid arthritis and normocytic anaemia irrespective of plasma ferritin concentration red cell ferritin content did not differ significantly from that for nonanaemic patients with rheumatoid arthritis for 27 patients with rheumatoid arthritis and microcytic anaemia the mean red cell ferritin content for patients with a plasma ferritin concentration in the 13110 microgramsl range was appreciably reduced it was indistinguishable from that for patients with rheumatoid arthritis and classical iron deficiency anaemia indicated by plasma ferritin concentrations of less than 12 microgramsl in contrast the mean red cell ferritin content for patients with rheumatoid arthritis microcytic anaemia and plasma ferritin concentrations above 110 microgramsl did not differ from that for patients with rheumatoid arthritis and normocytic anaemia oral treatment with iron in patients with rheumatoid arthritis microcytic anaemia and appreciably reduced red cell ferritin concentrations was accompanied by significant increases in haemoglobin concentration p less than 001 mean corpuscular volume p less than 001 and red cell ferritin contents p less than 005 this treatment however did not produce any appreciable change in haemoglobin concentration in patients with rheumatoid arthritis normocytic anaemia and normal red cell ferritin contents these findings suggest that the indices for iron deficiency in patients with rheumatoid arthritis and anaemia should include peripheral blood microcytosis together with a plasma ferritin concentration of less than 110 microgramsl