Influence of diurnal variation and fasting on serum iron concentrations in a community-based population

Serum iron concentrations remain reasonably stable during most daytime hours for testing purposes. In adults, blood collection after 5 to 9 h fasting provides a representative estimate of a patient's iron levels. For patients who have fasted overnight, i.e. ≥ 12 h fasting, clinicians should be aware that iron concentrations may be elevated beyond otherwise usual levels.