Transferrin receptor, soluble

Our body needs iron absorbed from food. Transferrin is a protein that binds iron and carries it into tissues and cells. Transferrin carries approximately 80% of iron into bone marrow. From there, it is transported to haemoglobin in the red blood cells. The rest of the iron is stored in cells and tissues as ferritin or hemosiderin.

When iron binds to transferrin, the resulting combination binds to transferrin receptors in cells. When transferrin receptors shed from the cell surface into circulation, they become soluble transferrin receptors (S-TfR). Normally, the TfR level is directly proportional to the number of formed red blood cells, and it also reflects changes in red blood cell production.

As the amount of iron decreases, cells produce more transferrin receptors. In that case, transferring receptors shed from the cell surface into circulation and the number of soluble transferrin receptors increases.

Because red blood cells live for approximately 120 days, bone marrow has to continuously produce new red blood cells. If you do not get enough iron from food or in case of bleeding, for example, the amount of iron stored in the body decreases. In time, this leads to iron deficiency. Red blood cell production is decreased, and the new red blood cells are smaller and contain less haemoglobin. This leads to iron deficiency anaemia.

When should TfR be measured?

TfR is measured to monitor the iron balance in the body and the status of storage iron, examine possible iron deficiency and the cause of anaemia. It also helps to determine the cause of anaemia related to chronic diseases.

TfR should be measured in case of the following symptoms, for example:

• Weakness, fatigue
• Lack of energy
• Paleness
• In complete blood count (CBC), haemoglobin (Hb) low and small red blood cells (MCV low)

According to the current view, TfR is the best test for determining the cause of the so-called microcytic anaemia (Greek word mikros means ‘small’, kytos means ‘cell’). Typically, microcytic anaemia is caused by iron deficiency and it can be determined by TfR.

What does the TfR test measure?

The test measures the number of soluble transferrin receptors in blood and helps to evaluate iron deficiency and diagnose iron deficiency anaemia. An S-TfR test can be used to measure the amount of iron available for use in the body. Iron concentration reflects possible changes in red blood cell production. Concentrations of soluble transferrin receptors only react to chronic diseases, not to inflammatory conditions or infections. The test helps to determine if anaemia is caused by a chronic disease (kidney problems, chronic inflammatory conditions, certain cancers) or iron deficiency.