Ferritin vs serum iron — which is the better iron marker?
Ferritin is the better stores marker — it reflects total body iron and falls early in depletion. Serum iron is highly variable hour-to-hour and is most useful as part of a panel (with TIBC and transferrin saturation) to characterize the type of iron disorder.
Full answer
Ferritin and serum iron measure different things. Ferritin is the body's iron storage protein and reflects total body iron reserves — it falls early in iron depletion, before hemoglobin or serum iron move, which is why it is the most sensitive routinely available marker of iron status. Serum iron, by contrast, measures the iron currently circulating bound to transferrin. It fluctuates significantly hour-to-hour with dietary intake, diurnal rhythm, and recent supplementation, so a single serum iron in isolation is hard to interpret. Serum iron is most useful as part of a panel — read with total iron binding capacity (TIBC) and transferrin saturation — to characterize the type of iron disorder (deficiency vs anemia of chronic disease vs iron overload). For routine iron screening, ferritin first.
Educational. Not a substitute for individualized provider review.
- Ferritin — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29