In the absence of inflammation, serum ferritin reflects total body iron content and guidelines for iron deficiency and iron deficiency anaemia in digestive diseases suggest that a level <30 ng/mL are suggestive of iron deficiency (see table below)1,2.
However, in patients with chronic conditions, such as cancer, inflammatory bowel disease, coeliac disease or infection, ferritin levels may not be reliable indicator. Functional iron deficiency can occur with inflammation as a result of hepcidin-mediated blockade of iron stores despite normal or even elevated ferritin2.
Table 2. Serum parameters for differential diagnosis of iron deficiency with and without inflammation2,3
Determining the inflammatory contribution to iron deficiency
Inflammation can be assessed by measurement of C-reactive protein or erythrocyte sedimentation rate and should be undertaken to aid diagnosis4. Identification of iron deficiency associated with inflammation has implications for treatment since hepcidin can block intestinal absorption of oral iron supplements meaning that IV iron is likely to be more effective and better tolerated1,4,5 (see 'Treating iron deficiency in patients with gastrointestinal disorders' section).
The transferrin saturation (TSAT) indicates the percentage of transferrin loaded with iron in plasma, and thus gives an indication of the amount of iron being released from iron stores for utilisation. A TSAT level below 16–20% indicates iron deficiency (either absolute or functional)2,4.