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The aged and dead red blood cells, which have lost the ability to function in full, are replaced by young blood cells. What happens with the hemoglobin (Hb) that is a part of these cells, which contains iron valuable for the body? Since it is able to pass through the glomeruli of the kidneys, it means that it is possible to dissolve in the blood plasma and, leaving the body, remove iron.
This compound is not able to overcome the narrow channels of the glomeruli of the kidneys, and hemoglobin remains in the body. The term “haptoglobin” comes from the Latin “hapto” – to bind.
Blood plasma is able to dissolve hemoglobin in the amount of 0,01-0,03 g/l. If its concentration in the blood is significantly increased, haptoglobin is not able to bind all the available hemoglobin. In this case, the red blood pigment in the plasma enters the kidneys, where filtration occurs. So there is hemoglobinuria (protein in the urine) and other complications. This situation most often occurs as a result of a blood transfusion.
About the norm of haptoglobin in the blood
Normally, haptoglobin successfully performs its functions. The table shows the age norms of this protein.
Age | Norm, mg/l |
Infants up to six months of age | 50 – 480 |
Children from 6 months and teenagers up to 16 years | 250 – 1380 |
Adults 16 to 60 years old | 150 – 2000 |
People over 60 | 350 – 1750 |
In the specialized medical literature, other normal ranges of haptoglobin may be given. this is because each laboratory has its own reference values. To determine the concentration of haptoglobin, blood serum taken on an empty stomach is analyzed using the immunoturbidimetric method. When identifying this glycoprotein, modern high-precision biochemical analyzers are used.
Haptoglobin in the human circulatory system
Haptoglobin is produced by the cells of the liver parenchyma. In the blood, it is represented by three hereditary phenotypes: HPT 1-1, HPT 2-1 HPT 2-2. Constantly present in the blood plasma, Haptoglobin takes 1,4% of the total protein.
Stages of HPT metabolism:
The protein binds to the hemoglobin released from the destroyed blood cells.
In connection with it, it creates a dispersed complex Hp-Hb, heading to the system of macrophages that process waste biomaterial.
Under the action of macrophages, iron molecules are released.
The released iron enters the circulatory system, where it combines with the protein transferrin and together with it enters the bone marrow to participate in the formation of new red blood cells.
Since Haptoglobin has a high peroxidase activity, in addition to binding hemoglobin, it inhibits the oxidative processes of lipids.
What does an increase in haptoglobin mean?
The concentration of haptoglobin increases with the following diseases and conditions:
Large-focal myocardial infarction;
Actively flowing rheumatic heart disease;
Acute phase of the inflammatory process;
The presence of a tumor;
Nephrotic syndrome, which is expressed in severe pathology of the kidneys due to a violation of the metabolism of lipids and proteins;
Lymphogranulomatosis;
Rheumatoid polyarthritis;
Stagnation of bile and violation of its excretion;
Hormonal therapy with corticosteroids.
What does a decrease in haptoglobin mean?
At any stage of the life cycle of red blood cells (erythrocytes), a drop in the concentration of haptoglobin can occur.
Types of hemolysis that provoke a decrease in the level of haptoglobin:
Isoimmune – occurs when blood is transfused that is incompatible in group (for example, repeated transfusion of Rh-positive blood to an Rh-negative recipient);
Autoimmune – occurs when antibodies are formed that are directed to their own antigens;
Mechanical – occurs as a result of a severe injury, when replacing heart valves with artificial analogues;
Medication – occurs when taking drugs based on pyrazole: Antipyrine, Amidopyrine, Analgin, or when taking sulfonamides;
Infectious – occurs with malaria, bacterial endocarditis;
Hemolysis in acute or chronic inflammation of the liver parenchyma.
The following pathologies cause a similar effect: enlargement of the spleen, abnormalities of erythrocyte membranes, hemoglobinopathies, anemia caused by folic acid deficiency, deficiency of glucose-6-phosphate dehydrogenase.
Features of haptoglobin
The behavior of haptoglobin sometimes differs from the functioning of analogous acute phase proteins. Since it is produced by the liver parenchyma, its hepatocytes contribute to an increase in HPT in the blood. But an analysis of blood biochemistry does not always confirm the fact of an increase in the concentration of haptoglobin.
With hemolysis accompanying acute inflammatory reactions, the amount of hemoglobin in the blood is very high. The creation of heavily dispersed complexes and their transportation to the macrophage system is required. In this case, the concentration of Haptoglobin should decrease. To obtain an objective picture without taking into account the effect of hemolysis, it is important to compare the results obtained with similar tests obtained when diagnosing other proteins from the category of acute phase proteins.