Ferritin

Ferritin is the gold standard test that reflects total body iron stores. As the ferritin falls below 50 μg/L the positive likelihood ratio for iron deficiency progressively increases above 1 (see Table 1). In a retrospective study at St. Michael’s Hospital, 90% of women were iron deficient.

 
Ferritin is an acute-phase reactant and levels can be elevated in the face of inflammation.  In the absence of an active comorbidity and/or inflammation, a ferritin value >100 μg/L suggests adequate iron stores and a low likelihood of iron deficiency.