TIBC test: normal range and what the result means

TIBC (total iron-binding capacity) measures how much iron could bind to the proteins circulating in the blood — mostly to transferrin, which is the main iron-transport protein in blood. Because transferrin is usually not fully saturated with iron, TIBC essentially shows the free transferrin “capacity” still available for iron. This test is most often done together with the iron level in blood and transferrin saturation (the percentage of transferrin places already taken by iron). Together, these three tests make up the iron panel, which helps to tell iron deficiency apart from iron overload or other conditions affecting iron metabolism. TIBC also reflects the amount of transferrin indirectly, because transferrin production changes with the body's iron stores and general state of health (for example liver function or inflammation). A single TIBC result is rarely assessed on its own — its meaning becomes clear together with the iron level and the symptoms.

• When a full blood count shows signs that iron may be lacking or that there may be too much of it
• When iron-deficiency anaemia is suspected — together with the iron level and transferrin saturation
• When iron overload in the body (haemochromatosis) is suspected
• When assessing anaemia related to a chronic illness
• When iron-deficiency anaemia needs to be told apart from other kinds of anaemia (for example thalassaemia)

According to MedlinePlus, a raised TIBC is considered to be linked to a decreased amount of iron in the body — transferrin's “free places” for iron increase when iron is lacking. The most common cause is iron-deficiency anaemia. TIBC is always assessed together with the iron level and transferrin saturation, and not on its own. Causes named by the source:

• Iron-deficiency anaemia — not enough iron in food, or poor absorption of it
• Long-term bleeding from the digestive tract
• Heavy menstrual periods
• Pregnancy — an increased need for iron

Alongside a raised TIBC, the following are usually looked at: the iron level in blood and transferrin saturation, which together help to confirm iron deficiency; a full blood count (haemoglobin, haematocrit), which shows whether anaemia is already present; a possible cause of bleeding, especially in men and in women after the menopause; and diet, along with conditions that interfere with iron absorption.

According to MedlinePlus, a low TIBC is considered to be linked to iron overload in the body, or to conditions that reduce the amount of transferrin — liver disease, for example. In that case transferrin's “free places” for iron become fewer, because there is already enough iron, or too much of it. Causes named by the source:

• Iron overload in the body (haemochromatosis)
• Liver diseases
• A chronic illness that affects protein production
• Inflammation in the body

Alongside a low TIBC, the following are usually looked at: the iron level in blood and transferrin saturation, which together help to assess iron overload; liver markers (ALT, AST), to judge liver function; family history — whether haemochromatosis has occurred in the family; and when to repeat the test, so that a change over time can be seen.

Read next

• Iron blood test — the iron level in blood, which is assessed together with TIBC
• Full blood count — haemoglobin and haematocrit show whether anaemia is already present
• Haemoglobin test — one of the full blood count values named above
• Ferritin test
• Tests for anaemia