Unsaturated (latent) iron-binding capacity

Why this test?

To determine the amount of iron in the body and its relationship with blood proteins (together with an analysis of iron in the serum, sometimes with a test for the total iron-binding ability of the serum and for transferrin). 

These studies make it possible to calculate the percentage of transferrin saturation with iron, that is, to determine exactly how much iron the blood carries. This indicator most accurately characterizes iron metabolism.

The purpose of such tests is to diagnose iron deficiency or excess. In patients with anemia, they allow us to find out whether the disease is caused by iron deficiency or other causes, such as a chronic disease or vitamin B12 deficiency.

In what cases is it prescribed?

When any abnormalities are found in the general blood test, hemoglobin test, hematocrit, erythrocyte count (together with the serum iron test). 

If a deficiency or excess of iron in the body is suspected. With a severe lack of iron, there is shortness of breath, pain in the chest and head, weakness in the legs. Some have a desire to eat unusual foods (chalk, clay), burning of the tip of the tongue, cracks in the corners of the mouth. Children may have learning difficulties. In case of suspicion of an overload of the body with iron (hemochromatosis).

This condition manifests itself in different ways, for example, pain in the joints or in the abdomen, weakness, fatigue, decreased sexual desire, heart rhythm disorders. When observing the effectiveness of treatment of iron deficiency or excess.

Testing preparation 

Stop taking medicines containing iron 72 hours before the testing. 

Test information 

Iron is an important trace element in the body. It is part of hemoglobin, which fills red blood cells and allows them to carry oxygen from the lungs to organs and tissues. Iron is a part of the muscle protein myoglobin and some enzymes. It is absorbed from food and then transferred by transferrin, a special protein produced in the liver. 

Usually, the body contains 4-5 g of iron, about 3-4 mg (0.1% of the total amount) circulates in the blood in connection with transferrin. The level of transferrin depends on the functioning of the liver and on human nutrition. Normally, 1/3 of the binding centers of transferrin are filled with iron, the other 2/3 remain in reserve. The index of serum latent iron-binding capacity (LTB) reflects how much transferrin is not filled with iron. 

This parameter can be calculated according to the following formula: LZZS = ZZZZS - iron in serum (ZZZS is the total iron-binding capacity of blood serum - an indicator that characterizes the maximum possibility of transferrin to be filled with iron). With iron deficiency, transferrin becomes more, so that this protein can connect with a small amount of iron in the serum. Accordingly, the amount of transferrin unoccupied by iron also increases, i.e. the latent iron-binding capacity of the serum. Conversely, with an excess of iron, almost all binding centers of transferrin are occupied by this trace element, so the latent iron-binding capacity of the serum decreases.

The amount of serum iron can vary significantly on different days and even within one day (especially in the morning hours), however, ZZZZS and LZZZZ normally remain relatively stable. In the early stages, iron deficiency sometimes does not show any symptoms. If a person is otherwise healthy, the disease can make itself felt only when the hemoglobin drops below 100 g/l. These are usually complaints of weakness, fatigue, dizziness, headache.