⚕️ Educational content only. This article explains what iron studies measure and what the results generally indicate. It is not medical advice. Speak with your doctor or healthcare provider for interpretation in the context of your personal health.
Iron studies are a panel of blood tests that assess the body’s iron status — measuring how much iron is circulating in the blood, how much is stored, and how well the body’s iron transport system is working. They are used to investigate anaemia, monitor iron deficiency treatment, assess iron overload conditions, and evaluate chronic disease. Understanding iron studies requires knowing what each individual test measures and how the results fit together as a pattern.
Key Takeaways
- Ferritin is the most reliable marker of iron stores — low ferritin indicates iron deficiency even if other markers appear normal.
- Serum iron measures circulating iron but is highly variable day-to-day; it is most useful interpreted alongside other iron markers.
- TIBC (total iron-binding capacity) reflects the capacity of transferrin to carry iron; it rises in iron deficiency and falls in chronic disease.
- Transferrin saturation is calculated from serum iron and TIBC; low saturation confirms iron deficiency, very high saturation suggests iron overload.
- Iron deficiency anaemia and anaemia of chronic disease can look similar on a full blood count but are distinguished by the iron studies pattern.
Ferritin
Ferritin is the protein that stores iron inside cells. A small amount leaks into the bloodstream, and measuring serum ferritin gives an indirect but reliable estimate of total body iron stores. Ferritin is the most clinically useful marker for diagnosing iron deficiency: a low ferritin is highly specific for depleted iron stores. Typical reference range: 15–200 µg/L for women, 30–300 µg/L for men (varies by laboratory and age). However, ferritin is also an acute phase reactant — it rises in inflammation, infection, liver disease, and malignancy, which can falsely normalise or elevate ferritin even when iron stores are genuinely low. This means a normal or high ferritin does not rule out iron deficiency in the presence of active inflammation.
Serum Iron
Serum iron measures the amount of iron bound to transferrin in the plasma. It is highly variable — it fluctuates throughout the day (diurnal variation), is affected by recent meals, and changes rapidly with acute illness or supplementation. For this reason, serum iron should not be interpreted in isolation. It is most useful as part of the full iron studies panel. Low serum iron occurs in iron deficiency and anaemia of chronic disease. High serum iron occurs in iron overload conditions (such as hereditary haemochromatosis) and in haemolysis. Typical reference range: 10–30 µmol/L (varies widely by laboratory).
TIBC (Total Iron-Binding Capacity)
TIBC measures the maximum amount of iron that can be bound and transported by transferrin in the blood. Transferrin is the main iron transport protein, produced by the liver. When iron stores are low, the liver produces more transferrin to try to capture as much iron as possible — so TIBC rises in iron deficiency. When iron stores are adequate or iron is in excess, transferrin production is reduced — TIBC falls. In chronic disease or malnutrition, transferrin synthesis also falls, reducing TIBC. Typical reference range: 45–80 µmol/L. Some laboratories measure transferrin directly rather than calculating TIBC, but both reflect the same underlying physiology.
Transferrin Saturation
Transferrin saturation is calculated as (serum iron ÷ TIBC) × 100% and expresses what percentage of transferrin binding sites are occupied by iron. Normal saturation is approximately 20–45%. Low transferrin saturation (below 16–20%) confirms iron deficiency: there is little iron available to bind to transferrin. High transferrin saturation (above 45–50%) raises concern for iron overload: transferrin binding sites are nearly fully occupied, and iron begins to deposit in tissues. In hereditary haemochromatosis, transferrin saturation above 45% is a key screening finding, particularly when combined with elevated ferritin.
Interpreting the Patterns
Iron deficiency (pre-anaemia stage): low ferritin, normal serum iron, raised TIBC, low transferrin saturation. Iron deficiency anaemia: low ferritin, low serum iron, raised TIBC, low transferrin saturation, low haemoglobin on FBC with microcytic hypochromic red cells. Anaemia of chronic disease: normal or high ferritin, low serum iron, low or normal TIBC, low transferrin saturation — the body is withholding iron from circulation as part of the inflammatory response (iron sequestration). Iron overload (e.g., haemochromatosis): high ferritin, high serum iron, low or normal TIBC, high transferrin saturation. Mixed iron deficiency and chronic disease (common in clinical practice): ferritin may be in the low-normal range, making interpretation challenging; additional markers (e.g., reticulocyte haemoglobin content, soluble transferrin receptor) may help.
Common Conditions Investigated with Iron Studies
Iron deficiency anaemia is the most common nutritional deficiency worldwide. Causes include inadequate dietary intake, poor absorption (coeliac disease, gastric surgery), blood loss (menstruation, gastrointestinal bleeding), or increased demand (pregnancy). Hereditary haemochromatosis is a common inherited condition (particularly among people of northern European ancestry) in which iron is absorbed in excess and deposited in organs such as the liver, heart, joints, and pancreas. Secondary iron overload can occur in conditions requiring repeated blood transfusions (e.g., thalassaemia). Anaemia of chronic disease occurs in the context of chronic infection, inflammation, autoimmune conditions, or malignancy.
References
- National Library of Medicine. Iron Tests. MedlinePlus. https://medlineplus.gov/lab-tests/iron-tests/
- NHS. Iron deficiency anaemia. https://www.nhs.uk/conditions/iron-deficiency-anaemia/
- World Health Organization. Iron deficiency anaemia: assessment, prevention, and control. WHO. 2001.
- Ganz T. Hepcidin and iron regulation, 10 years later. Blood. 2011;117(17):4425–4433.
- Brissot P, Pietrangelo A, Adams PC, et al. Haemochromatosis. Nature Reviews Disease Primers. 2018;4:18016.