Transferrin and transferrin saturation (TSAT)

Transferrin is the transport protein for iron in the blood and is made in the liver. Transferrin saturation (TSAT) indicates what share of its binding sites is currently occupied by iron. It is calculated from serum iron and transferrin; both values are measured in serum. While ferritin reflects the iron stores, transferrin saturation shows how much iron is currently in circulation and available to the bone marrow for blood formation. Because serum iron fluctuates during the day and after meals, the saturation is considered together with ferritin, the blood count and inflammation values.

What transferrin does in the body

Each transferrin molecule can bind two iron atoms. It takes over iron where it is released into the blood: from the cells of the gut lining after absorption from food, and from scavenger cells that break down old red blood cells and recycle the iron. Via transferrin receptors the iron enters the cells, above all the blood-forming cells of the bone marrow, which need it for haemoglobin. Tightly bound iron is harmless; free iron would promote the formation of aggressive oxygen radicals. The liver makes more transferrin when the iron stores are empty and less during inflammation. The hormone hepcidin controls how much iron enters the blood in the first place.

Low transferrin saturation – what happens in the body?

When saturation is low, too little iron reaches the bone marrow. The red blood cells become smaller and contain less haemoglobin; over time anaemia develops. The blood then carries less oxygen, which can show as tiredness, pallor, breathlessness on exertion, palpitations, brittle nails and hair loss. Two routes lead there: in true iron deficiency the stores are empty, ferritin is low and transferrin high – for example due to blood loss, low intake or impaired absorption in the gut. In functional iron deficiency the stores are full, but inflammation raises hepcidin, which blocks the release of iron into the blood; transferrin is then rather low.

High transferrin saturation – what happens in the body?

High saturation means that more iron is in transit in the blood than transferrin can safely bind. Iron that is not bound to transferrin then appears. It is preferentially taken up by the liver, heart, pancreas and joints and is deposited there. Free iron promotes the formation of oxygen radicals that can damage cells; over years this can lead to liver damage, joint pain, heart rhythm disorders and disorders of sugar metabolism. A common hereditary cause is haemochromatosis, in which a gene variant reduces hepcidin formation and the gut absorbs too much iron. Iron preparations or infusions shortly before the blood sample, frequent blood transfusions, increased breakdown of red blood cells and liver disease also raise the value.

The interpretation is given in your report.