Iron Studies Interpretation
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Direct answer
Iron studies interpret body iron status by pairing serum ferritin, which reflects storage iron, with transferrin saturation and total iron-binding capacity (TIBC), which reflect circulating iron. Low ferritin with high TIBC and low transferrin saturation indicates iron deficiency, while high ferritin with high transferrin saturation points to iron overload. Inflammation raises ferritin and lowers TIBC, so the pattern must always be read with CRP.
What you must remember
- Ferritin: the best single test of storage iron; a value below about 15 µg/L indicates iron deficiency when no inflammation is present.
- Ferritin as an acute-phase reactant: rises with infection, inflammation, liver disease, malignancy and alcohol, so it can falsely reassure in iron deficiency.
- TIBC: raised in iron deficiency because transferrin synthesis increases, and low in chronic disease and haemochromatosis.
- Transferrin saturation: serum iron divided by TIBC, expressed as a percentage; below about 16 to 20 percent suggests restricted iron supply, and above 45 percent raises suspicion of haemochromatosis.
- Serum iron: varies through the day and after meals, so it is unreliable on its own and is interpreted only with saturation and ferritin.
- Soluble transferrin receptor: raised in iron deficiency but not in chronic disease, which helps separate combined deficiency from anaemia of chronic disease.
- Haemochromatosis: HFE C282Y homozygosity is the commonest cause, with raised ferritin and saturation; liver iron can be quantified by MRI.
- Anaemia of chronic disease: low serum iron and TIBC with normal or raised ferritin, because iron is sequestered in macrophages.
Patterns across the three conditions
Iron studies are best read as a pattern rather than as isolated values. The table sets out the classic combinations.
| Pattern | Ferritin | TIBC | Transferrin saturation |
|---|---|---|---|
| Iron deficiency | Low | High | Low |
| Anaemia of chronic disease | Normal or high | Low | Low to low-normal |
| Deficiency with inflammation | Falsely normal | Low to normal | Low |
| Iron overload | High | Low | High, above 45 percent |
A low ferritin is nearly diagnostic of iron deficiency, but a normal ferritin during inflammation does not exclude it. Where ferritin falls in an intermediate zone, CRP is measured first, because inflammation changes what the ferritin value means. Soluble transferrin receptor is then used to settle the diagnosis when the picture remains mixed.
Iron overload is suspected when ferritin and saturation are both high, but liver disease, alcohol and transfusion can raise ferritin without true overload. A raised saturation is therefore the more specific marker.
In a previously healthy adult with a low ferritin, the diagnosis is usually straightforward. In patients with liver disease, chronic kidney disease or malignancy, the same value must be read against CRP and the full pattern before it is acted upon.
Where the exam tries to catch you
Iron questions turn on the interpretation of ferritin in the presence of inflammation or chronic disease.
- Trap: reassuring a patient whose ferritin is 40 during an infection Correct: inflammation raises ferritin falsely, so CRP and other markers must be assessed before ruling out iron deficiency.
- Trap: using serum iron alone to diagnose iron deficiency Correct: serum iron varies through the day, so transferrin saturation and ferritin are preferred.
- Trap: giving oral iron for anaemia of chronic disease Correct: iron is trapped in macrophages, so oral iron does not correct the anaemia; the underlying disease is treated.
- Trap: labelling high ferritin as iron overload without checking saturation Correct: a high ferritin from liver disease or inflammation does not confirm overload, and a saturation above 45 percent supports haemochromatosis.
Frequently asked questions
What does a low ferritin with high TIBC indicate?
A low ferritin with high TIBC indicates iron deficiency, because storage iron is depleted and transferrin synthesis rises to capture more iron. Transferrin saturation is typically low in this pattern, confirming reduced circulating iron.
How does inflammation affect iron studies?
Inflammation raises serum ferritin as an acute-phase reactant and lowers TIBC, which can mask iron deficiency or mimic overload. Measuring CRP alongside iron studies helps interpret a borderline ferritin in an inflamed patient.
What transferrin saturation suggests haemochromatosis?
A transferrin saturation above about 45 percent, especially with a raised ferritin, raises suspicion of hereditary haemochromatosis. HFE gene testing, most commonly for the C282Y mutation, is the next step to confirm the diagnosis.
Why is serum iron alone unreliable?
Serum iron varies through the day and after meals, and it falls in inflammation even without iron deficiency. Transferrin saturation and ferritin provide more stable information for interpretation.
What do iron studies show in anaemia of chronic disease?
Anaemia of chronic disease shows low serum iron and TIBC with normal or raised ferritin, because iron is sequestered in macrophages rather than lost. Oral iron does not correct this anaemia, which needs treatment of the underlying disease.