Transferrin saturation: what the result means (TSAT)

Transferrin is a protein in blood plasma that carries iron from the intestine and from the body's iron stores (the liver, the spleen) to the bone marrow, where it is used to make red blood cells. Transferrin saturation shows what percentage of all the transferrin present is bound to iron at that moment — it is calculated from the serum iron level and the total iron-binding capacity (TIBC). Because the amount of iron in the blood fluctuates through the day depending on food, while transferrin changes more slowly, this ratio helps to assess more accurately whether the body has enough iron, is short of it, or has an excess. Transferrin saturation is most often assessed together with ferritin, the iron level in the blood and TIBC, because each of these markers reflects a different side of iron metabolism. Together they make it possible to distinguish iron-deficiency anaemia from other anaemias or from iron-overload conditions such as haemochromatosis.

• When a full blood count shows a reduced haemoglobin or haematocrit — when iron-deficiency anaemia is suspected
• When there is weakness, tiredness, dizziness, shortness of breath or heart rhythm disturbances
• When iron excess (haemochromatosis) is suspected — with joint pain, abdominal pain or changes in skin colour (a greyish, metallic or bronze tint)
• To distinguish iron-deficiency anaemia from other kinds of anaemia, for example thalassaemia
• To monitor the course of treatment with iron preparations or of iron-removal procedures

A raised transferrin saturation is considered a sign of iron excess according to MedlinePlus. The most common cause is inherited iron accumulation (haemochromatosis), but the value can also be raised by liver disease, haemolytic anaemia or frequent blood transfusions. Ferritin and liver markers help to tell the causes apart.

Causes of a raised result:

• Haemochromatosis — inherited accumulation of iron in the body
• Liver disease
• Haemolytic anaemia
• Frequent blood transfusions or iron poisoning
• Some medicines, for example oral contraceptive pills or oestrogen preparations

Symptoms sometimes reported alongside iron excess:

• Weakness or tiredness
• Joint pain (most often the knees or the hands)
• Abdominal pain
• Changes in skin colour — a greyish, metallic or bronze tint
• Reduced sex drive or erectile problems

What to discuss with a doctor:

• Ferritin and liver markers (ALT, AST, GGT) — they help to separate haemochromatosis from other causes
• Family history: whether anyone in the family had an iron-accumulation condition
• Whether any medicines that could affect the result were being taken at the time of the test
• When to repeat the test so that the change over time is visible

A reduced transferrin saturation most often indicates iron deficiency and is one of the signs of iron-deficiency anaemia. The cause can be too little iron in food, blood loss or poor iron absorption. The marker is usually assessed together with iron, ferritin and TIBC.

Causes of a reduced result:

• Iron-deficiency anaemia — too little iron in food or poor absorption of it
• Long-term bleeding from the gastrointestinal tract or heavy periods
• Pregnancy — an increased need for iron
• Other kinds of anaemia, for example thalassaemia — an inherited blood disorder

Symptoms sometimes reported alongside iron deficiency:

• Weakness or tiredness
• Dizziness
• Shortness of breath
• Heart rhythm disturbances

What to discuss with a doctor:

• A full blood count and ferritin — so that it is clear whether anaemia is already present and how severe it is
• A possible cause of blood loss — particularly in men and in women after menopause
• Diet and digestive tract conditions that interfere with iron absorption
• When to repeat the test to assess the change after treatment

Which tests it is assessed with

Transferrin saturation is most often assessed together with the iron level in the blood, ferritin and total iron-binding capacity (TIBC). Together these markers help to distinguish iron deficiency from iron excess or from other causes of anaemia, because each of them reflects a different side of iron metabolism.