Ferritin vs Serum Iron: what's the difference?
Educational — not medical advice · Ranges vary between laboratories
The short answer: Serum iron is the iron circulating in your blood right now. Ferritin is the iron in storage. Ferritin is the fuel tank and serum iron the fuel line — which is why ferritin below about 30 ng/mL is the earliest and most sensitive sign that iron is running short.
Ferritin is the protein that warehouses iron in your body. Low ferritin with normal hemoglobin means you're running on reserve; treating at this stage prevents full anemia.
Full Ferritin guideSerum iron measures the amount of iron currently circulating in the blood, bound to a transport protein called transferrin. It reflects how much iron is available right now for the body to use, which can shift throughout the day and after meals.
Full Serum Iron guideAt a glance
| Ferritin | Serum Iron | |
|---|---|---|
| Panel | Iron studies | Iron studies |
| Unit | ng/mL | µg/dL |
| Typical adult range | Normal 30–300 ng/mL | Normal 60–170 µg/dL |
| Also known as | Serum Ferritin | iron, serum Fe |
General adult reference intervals — your lab's printed range takes precedence.
Why they're often tested together
Serum iron swings through the day, peaking in the morning and shifting after meals or supplements, so labs interpret it alongside ferritin and TIBC rather than alone. Serum iron can read normal while stores are already depleted, so the pair answers two different halves of the same question.
Questions people ask
Can ferritin be high without extra iron?
Yes. Ferritin rises with inflammation or infection even when iron itself is normal, and liver conditions can lift it too. That's one reason a high ferritin is read alongside the rest of the iron studies rather than taken as iron overload by default.
Why is a morning sample preferred for serum iron?
Iron levels naturally rise and fall with meals, recent supplements, and the body's internal clock, typically peaking in the morning. A consistent fasting morning draw makes results comparable from one test to the next.
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