People who are not pregnant:

• Serum ferritin level is the biochemical test which most reliably correlates with relative total body iron stores. Low levels indicate low iron stores. However, the test is difficult to interpret if infection or inflammation is present, as levels can be high even in the presence of iron deficiency [WHO et al, 2001].
• A serum ferritin level of less than 15 microgram/L confirms the diagnosis of iron deficiency anaemia [British Society of Gastroenterology, 2005; Smellie et al, 2006].
• A serum ferritin concentration of greater than 100 microgram/L usually rules out iron deficiency [Smellie et al, 2006; Killip et al, 2007]. However, expert feedback suggests that this may not be the case if a person has certain inflammatory diseases (e.g. malaria, tuberculosis) as the ferritin can be raised above 100 microgram/L even in the presence of iron deficiency anaemia.
• Ferritin levels of more than 15 micrograms/L are more difficult to interpret as they can be influenced by the presence of co-existing disease:
• Coexisting diseases in which ferritin levels may be misleading include rheumatoid disease, liver disease, malignancy, hyperthyroidism, kidney disease, or heavy alcohol intake. Feedback from expert reviewers suggests that this may also be the case with any disease in which C-reactive protein, erythrocyte sedimentation rate or globulins are increased [British Columbia Medical Association, 2004; Provan, 2007; Zimmerman and Hurrell, 2007].
• Expert opinion varies as to the level of ferritin which is diagnostic of iron deficiency anaemia in people with chronic inflammation. The British Society of Gastroenterology suggest a diagnostic cut-off of serum ferritin of 50 micrograms/L in people who have coexisting disease [British Society of Gastroenterology, 2005]; other reviews concerning the laboratory diagnosis of iron deficiency anaemia concluded that the likelihood of iron deficiency does not start to decrease until ferritin levels are higher than 70 micrograms/L in people with inflammatory or liver disease [Guyatt et al, 1992; Smellie et al, 2006].
• If inflammation is suspected to be spuriously affecting the ferritin result, practitioners need to consider other markers of inflammation (e.g. white blood cell count, platelets, C-reactive protein) or measures of iron status (e.g. iron, total iron binding capacity), and seek advice from haematology or clinical biochemistry if in doubt about selection of further tests and interpretation of results.

Pregnant women:

• Serum ferritin level is considered to be a reliable indicator of iron deficiency in the first trimester (in the absence of infection, inflammation, or excessive alcohol consumption); however serum ferritin levels fall in the second and third trimesters independent of iron stores [Mungen, 2003].