Haptoglobin

Why this test?

• To diagnose intravascular hemolysis and its severity.
• To detect acute phase reactions (infections, inflammation, tumors, burns, frostbite, autoimmune diseases).
• To assess liver function.

In what cases is it prescribed?

• In case of symptoms of hemolytic anemia (weakness, darkening of urine, pallor, yellowing of the skin).
• With a decrease in hemoglobin, red blood cells, the appearance of immature forms of red blood cells.
• When there is a probability of hemolysis (due to blood transfusion, artificial heart valves, hemodialysis, exposure to substances that destroy red blood cells - lead, dyes, sulfonamides, snake venoms).
• In case of liver diseases.

Test information

Haptoglobin is a plasma protein belonging to the alpha-2-globulin fraction. In the human body it is represented by three types: Hp 1-1, Hp 2-1, Hp 2-2. Hp 1-1 is a monomer, Hp 2-1, Hp 2-2 are polymers. Haptoglobin was discovered in 1938, its name is derived from the word hapto - ««to bind»«. It is synthesized in the liver and is constantly present in the blood plasma.

Pathological conditions that change the level of haptoglobin in the blood are acute phase reaction, liver and kidney damage, autoimmune diseases, hemolysis.

The function of haptoglobin is to bind hemoglobin and participate in the acute phase reaction. Hemoglobin is contained in red blood cells, delivers oxygen to tissues and participates in the transport of carbon dioxide. The life span of a red blood cell is 120 days. Most red blood cells are destroyed in the spleen and liver, but some of them are destroyed directly in the vessel with the release of hemoglobin into the bloodstream (intravascular hemolysis). Normally, the proportion of intravascular hemolysis is small. A small amount of hemoglobin binds to haptoglobin, then this complex is absorbed by cells of the reticuloendothelial system, for example, the spleen. Iron from hemoglobin returns to form red blood cells, as haptoglobin is involved in iron metabolism in the body. If the binding of free hemoglobin does not occur, it enters the kidneys and can lead to their damage.

The increased breakdown of red blood cells in the bloodstream leads to an increase in the intake of hemoglobin in the blood and, accordingly, to a decrease in the level of haptoglobin. Haptoglobin production during hemolysis is not enhanced. Thus, a decrease in the level of haptoglobin is an important sign of hemolysis, and it is intravascular hemolysis - hemolysis outside the bloodstream is not accompanied by a decrease in haptoglobin.

The decay of red blood cells occurs for various reasons. Hereditary defects of red blood cell components (hemoglobin, membranes, enzymes) make red blood cells less resistant to various hemolytic factors. Red blood cells can be destroyed in infectious diseases, such as infection with plasmodium malaria, hemolytic streptococcus, gas gangrene. Many substances of natural and artificial origin are hemolytic poison: dyes, lead, medicines, snake venoms, some mushrooms. Hemolysis can occur when transfusion of incompatible blood group, in case of conflict with Rh factor between mother and fetus. Enhanced breakdown of red blood cells occurs in people with artificial heart valves who receive hemodialysis. In all these cases, hemolytic anemia occurs, which is accompanied by pallor of the skin and mucous membranes, weakness, darkening of the urine, yellowing of the mucous membranes and skin. Kidney complications are possible due to damage to the kidneys by free hemoglobin.

Haptoglobin belongs to the proteins of the acute phase - it is produced in response to infection, damage, tumor process. Haptoglobin synthesis increases under the influence of growth hormone, insulin, bacterial endotoxins, prostaglandins and cytokines. In inflammation, it acts as an antioxidant, reducing cell damage, inhibits the growth of some bacteria, such as Escherichia Coli, suppresses inflammation by inhibiting the synthesis of prostaglandins. In addition, it stimulates the growth of blood vessels and participates in the regulation of the immune system. Thus, in case of inflammation, tumor growth, damage by chemical factors, the level of haptoglobin in the blood increases on the 4th-6th day after the onset of the harmful factor and stops 14 days after its disappearance.

In case of liver damage, its ability to produce proteins is impaired, which leads to a decrease in the amount of haptoglobin (as it is synthesized in the liver). In case of kidney damage, proteins that normally remain in the bloodstream, such as Hp 1-1, which has the smallest molecular weight among all types of haptoglobin, are lost in the urine. In these cases, the content of haptoglobin in the blood will decrease.

In autoimmune diseases, the activity of the enzyme involved in the synthesis of haptoglobin increases, which increases its concentration in the blood.

Most often, the haptoglobin test is used to diagnose hemolytic anemias and assess their severity.