Iron blood tests explained: ferritin, serum iron, TIBC

A report from an iron check can list several tests with similar names. This is what each one measures, in plain terms. MedlinePlus describes the first four; transferrin saturation is a calculation many laboratories add; the NHS describes the full blood count.

The tests

• Ferritin measures how much iron the body has stored.
• Serum iron measures the amount of iron circulating in the blood at that moment.
• Transferrin measures the protein that carries iron around the body.
• Total iron-binding capacity (TIBC) measures how much iron the blood could carry, which reflects how well iron attaches to transferrin and other proteins.
• Transferrin saturation, often printed as a percentage, relates the iron in the blood to the capacity to carry it. Your laboratory may calculate it from the others.
• A full blood count looks at the blood cells, including the red cells and their haemoglobin. The NHS says it is the usual first test for iron deficiency anaemia and needs no preparation.

Why several tests are used together

MedlinePlus says iron tests are ordered to check for low iron, which can lead to anaemia, or for high iron, to help identify the type of anaemia, to see how much iron the liver holds when liver disease is a concern, and to see whether treatment is working. No single number gives the full picture, so results are read together with symptoms, age, medical history and other tests.

Preparation and timing

MedlinePlus says you may be asked to fast for about 12 hours before iron tests and that they are usually done in the morning, because iron levels vary during the day and tend to be higher in the morning. It also notes that some medicines, including birth control pills and oestrogen, and the menstrual cycle can affect iron levels. Follow the instructions your laboratory gives you.

Units and ranges

Serum iron is printed in µmol/L on some reports and µg/dL on others, and ferritin in ng/mL, µg/L or pmol/L. Each laboratory publishes its own ranges in its own units. Record every result with its date and the unit exactly as printed.