How to separate iron deficiency anemia from anemia of chronic disease in a patient with a chronic inflammatory disease like RA?
In patients with uncomplicated IDA, measurement of iron status with serum level of iron (low), percent iron saturation (low), total iron-binding capacity (TIBC; high), and ferritin (low) are adequate. However, in patients with inflammatory disease, TIBC and ferritin can be normal as a result of the acute-phase response. Thus, to separate IDA from ACD, the gold standard is a bone marrow biopsy. However, studies have shown that a serum ferritin >100 ng/mL excludes iron deficiency in patients with an active inflammatory disease as indicated by an elevated ESR/CRP. Likewise, a serum ferritin <50–60 ng/mL, particularly when associated with an elevated serum transferrin receptor level, is highly specific for IDA in patients with RA.