Transferrin saturation: reading the percentage

Transferrin is the protein that shuttles iron through the blood. Each molecule has places to bind iron, and the transferrin saturation tells you what proportion of those places are filled. Lab Tests Online UK says it is a calculation that represents the percentage of transferrin saturated with iron and that it can be derived from the transferrin or TIBC value when the serum iron concentration is known.

Usually about one third of the transferrin measured is used to transport iron, so the figure sits well below the maximum in healthy people. When the body is short of iron, fewer sites are used and saturation falls. When there is too much iron, more sites are filled and saturation climbs.

Tests for iron, ferritin, transferrin saturation and TIBC may be requested when a doctor suspects chronic iron overload. In the absence of multiple transfusions, the most common cause of overload is hereditary haemochromatosis, a genetic condition. Lab Tests Online UK lists signs of overload as unexplained joint and muscle pain, fatigue and weakness, abdominal pain, loss of sex drive or fertility, and signs of liver disease, diabetes or heart problems.

The same panel is used when anaemia with small, pale red cells suggests iron deficiency, and when someone with a long-term illness has an unclear blood count. In iron deficiency, saturation is typically low.

Lab Tests Online UK says you may be asked to fast for 12 hours before iron tests, drinking only water, and not to take iron tablets for 24 hours because iron is absorbed rapidly and can make blood iron levels falsely high. Serum iron varies through the day and from day to day, which also means saturation can bounce around.

Because the calculation depends on serum iron, a single borderline result is often repeated, ideally as a morning fasting sample, before any conclusion is drawn.

A low saturation, especially with a high TIBC, usually indicates iron deficiency. The NHS says iron deficiency anaemia is often caused by blood loss or pregnancy, that heavy periods are a very common cause, and that bleeding in the stomach and intestines, caused for example by NSAIDs, ulcers, bowel inflammation or piles, is another common cause. Chronic inflammatory illness can also lower saturation, but in that case TIBC tends to be low or normal rather than high.

Treatment depends on the cause. The NHS describes iron tablets for about six months, advice on iron-rich foods, and repeat blood tests to confirm iron levels are returning to normal.

A raised saturation with a high serum iron, low or normal TIBC and high ferritin is the pattern Lab Tests Online UK associates with haemochromatosis. A raised value can also reflect recent iron intake, repeated transfusions, or iron poisoning, which most often happens in children who swallow iron tablets.

Where overload is suspected, HFE genetic testing may be requested to confirm hereditary haemochromatosis, and sometimes when there is a family history. Early detection matters because excess iron accumulates over years in the liver, joints, heart and pancreas.

A repeat fasting sample and ferritin usually follow an abnormal result. Low values lead to a search for blood loss or malabsorption and replacement. High values with a high ferritin lead to genetic testing and often a liver assessment, and treatment may involve removing blood regularly. Seek emergency care if a child may have swallowed iron tablets; call 999 or go to A&E.