Figure 2.

The definition of iron groups by joint transferrin saturation and ferritin quartiles (n=138,853). Four iron groups were established using quartiles of serum transferrin saturation and ferritin: reference, second and third quartiles of transferrin saturation and ferritin; low iron, first quartiles of transferrin saturation and ferritin; high iron, fourth quartiles of transferrin saturation and ferritin; and functional iron deficiency, first transferrin saturation quartile with third and fourth quartiles of ferritin. The ranges of transferrin saturation and ferritin values for each iron group are included. The table includes quartile thresholds of serum transferrin saturation and ferritin in the eligible cohort, including the excluded (not classified) subgroup.