Haematology
Transferrin Saturation
Iron status from serum iron and TIBC.
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Background
Transferrin saturation expresses the proportion of the iron-carrying protein transferrin that is occupied by iron, calculated as (serum iron ÷ total iron-binding capacity) × 100. It is a core component of iron studies and reflects the balance between circulating iron and the body's iron-binding capacity. A low saturation indicates that little transferrin is loaded with iron, while a high saturation indicates that transferrin is heavily loaded. It is interpreted alongside ferritin and the clinical picture to assess overall iron status.
Interpreting the result
A transferrin saturation below roughly 16% suggests iron deficiency, where circulating iron is low relative to binding capacity. A value in the normal range (approximately 16–45%) indicates adequate iron supply. A persistently raised saturation above about 45% suggests iron overload and is an important screening clue for hereditary haemochromatosis. Because results vary with diet and diurnal rhythm, a fasting morning sample is preferred, and abnormal values should be confirmed and interpreted with ferritin.
Worked example
A patient has a serum iron of 8 µmol/L and a TIBC of 80 µmol/L. Transferrin saturation = (8 ÷ 80) × 100 = 10%. This is below 16%, consistent with iron deficiency, and would typically be interpreted together with a low ferritin to confirm depleted iron stores.
Critical actions
Use the same units for iron and TIBC. Interpret with ferritin and the clinical picture.
Pearls / pitfalls
- Use the same units for serum iron and TIBC so they cancel in the ratio; interpret the percentage alongside ferritin, not in isolation.
- Take a fasting, morning sample where possible — serum iron varies with diet and through the day.
- Ferritin is an acute-phase reactant and can be normal or raised despite iron deficiency; a low transferrin saturation can help reveal deficiency in inflammatory states.
- A raised saturation is an important early clue to haemochromatosis, sometimes preceding a rise in ferritin — pursue confirmatory testing.
Evidence & validation
Transferrin saturation is a long-established laboratory index and is endorsed within haematology and haemochromatosis guidance — for example, a raised fasting transferrin saturation is a recommended screening test for hereditary haemochromatosis, with confirmatory ferritin and genetic testing.
Frequently asked questions
What transferrin saturation suggests iron deficiency?
A saturation below roughly 16% suggests iron deficiency, as little of the transferrin is loaded with iron. It is best interpreted together with a low ferritin, which confirms depleted iron stores.
What does a high transferrin saturation indicate?
A persistently raised saturation above about 45% suggests iron overload and is an important screening clue for hereditary haemochromatosis. It should prompt confirmatory ferritin and, where appropriate, genetic testing.
Why should the sample be taken fasting?
Serum iron, and therefore transferrin saturation, varies with recent food intake and follows a diurnal rhythm. A fasting morning sample gives a more reliable and reproducible result.
Why interpret transferrin saturation with ferritin?
The two give complementary information — saturation reflects circulating iron supply while ferritin reflects iron stores. Because ferritin rises with inflammation, combining the tests gives a more accurate picture of iron status.
References
- Transferrin saturation = (serum iron ÷ total iron-binding capacity) × 100; a standard component of iron studies.
- European Association for the Study of the Liver (EASL) Clinical Practice Guidelines on haemochromatosis; British Society for Haematology guidance on iron studies.
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