A recent study by Ahluwalia and colleagues used a discriminant statistical analysis approach to determine that a combination of serum ferritin, plasma transferrin receptor concentration, and erythrocyte sedimentation rate was the optimal set of variables for differentiating iron deficiency and the anemia associated with chronic disease in a group of elderly women. Iron deficiency was defined as a significant response in hemoglobin concentration after iron supplementation. The findings of this study suggest that iron deficiency can be relatively common among elderly anemic women with rheumatoid arthritis. Use of these three biochemical measures should be clinically useful to differentiate iron deficiency in the anemia of chronic disease.