Generality
Haptoglobin is a transport glycoprotein, whose function is to irreversibly bind the free hemoglobin molecules circulating in the blood. This allows the formation of an haptoglobin-hemoglobin complex, which is rapidly removed from the bloodstream and directed to the liver for iron recovery.
Under normal conditions, the concentration of haptoglobin is in equilibrium between the hepatic synthesis and its elimination.
Haptoglobin testing measures the amount in the blood. This assessment is mainly used to diagnose hemolytic anemia . When a large number of red blood cells undergoes destruction, in fact, the concentration of haptoglobin in the blood temporarily decreases, since the consumption of the protein is higher than the rate of production of the same by the liver.
What's this
Functions in the human organism
Haptoglobin is a protein mainly synthesized in the liver, and present in the blood at high concentrations (about one gram per liter of plasma). The task of the haptoglobin is to bind - in a specific and particularly effective way - the free hemoglobin in the serum, that is the protein molecule contained in the red blood cells and assigned to the transport of oxygen. In this way, haptoglobin prevents the urinary loss of hemoglobin and preserves iron.
Hemoglobin is formed from a protein part, the globine, and from a part that contains iron and binds oxygen, the EME; when the red blood cells die - for old age after 120 days or for other reasons (haemolytic anemias, traumas, etc.) - the haptoglobin, binding itself to it irreversibly, prevents its urinary elimination, allowing the recycling of iron and others its components.
The hemoglobin-haptoglobin complex, escaped from the renal filter, is rapidly eliminated by the endothelial reticulum system, where macrophages absorb iron and release it to transferrin; in turn, this transport protein conveys the mineral to the bone marrow, where it will be used to produce hemoglobin to be incorporated into the new red blood cells. The remaining part of EME is degraded to indirect bilirubin and transported to the liver, which, after having conjugated it with glucoronic acid, introduces it into the bile as direct bilirubin.
The total pool of circulating haptoglobin is able to bind about 3 grams of hemoglobin; consequently, in the case of massive hemolysis (high destruction of red blood cells), the haptoglobin is saturated (in practice the quantity of hemoglobin exceeds the share of available haptoglobin); the circulating free hemoglobin is then filtered by the renal glomeruli and reabsorbed by the cells of the proximal tubule, which complex the iron emic in ferritin and hemosiderin (there is an increase in sideruria and hemosideriuria, ie excessive presence of iron and hemosiderin in the urine) . In more advanced stages, hemoglobin exceeds the resorption capacity of the proximal tubule cells; in part it is then removed with urine (this is called hemoglobinuria), with possible renal damage.
The free haptoglobin, unlike the bound one, has a very long life and a half-life of about four days. The dosage methods evaluate the free fraction.
Why do you measure
The determination of haptoglobin is performed as a support in the diagnosis of a state of haemolytic anemia . This examination is indicated when the patient has symptoms that the doctor suspects may be due to the destruction of red blood cells, such as fatigue, shortness of breath, pallor or jaundice.
It should be noted, however, that the extent of haptoglobin cannot be used to diagnose the exact causes of hemolysis.
When is the exam prescribed?
Haptoglobin examination is indicated by the doctor if haemolytic anemia is suspected, based on symptoms (for example: pallor and fatigue) and findings indicative of the clinical picture, such as jaundice and dark urine.
In the event that a low or unexpectedly high haptoglobin value was found, the analysis can be repeated at a later time, to ascertain whether there are changes in the concentration of the protein.
Haptoglobin examination may be required together with:
- Total or indirect bilirubin test to evaluate liver function;
- Determination of LDH;
- Reticulocyte counts;
- Blood smear.
Normal values
NORMAL VALUES: 50-150 mg / dL (laboratory-to-laboratory variables).
High Haptoglobin - Causes
Among the drugs that can increase the levels of haptoglobin, we find the corticosteroids and androgens (the man has higher values than the woman); on the other hand, contraceptive pills, isoniazid, quinidine and streptomycin exert a diametrically opposite effect.
Haptoglobin is very low in the serum of newborns and reaches levels similar to those of adulthood around the fourth month of life.
Low Haptoglobin - Causes
Being synthesized by the liver, the plasma haptoglobin decreases in people with liver diseases (hepatitis, cirrhosis, neoplasias etc.). In this case the blood tests also show an alteration of the various indices of liver function (albumin decline, increase in AST and ALT etc.). The symptoms of anemia are missing (pallor, weakness, jaundice, etc.).
In addition to a reduced synthesis, haemoglobin blood concentrations can fall for increased consumption; is the case of hemolytic anemias.
- When the conspicuous destruction of red blood cells occurs in the intravascular area, in addition to low haptoglobin values, significant increases in serum free hemoglobin, indirect bilirubin and LDH are appreciated, accompanied by hemoglobinuria and hemosideruria. It is also possible to appreciate increases in reticulocytes (newly formed red blood cells), and reduced red blood cells, hematocrit and hemoglobin.
- If instead the hemolysis is established at the extravascular level (inside the spleen or liver), the haptoglobin falls within the norm, while there is a significant increase in reticulocytes.
Reduced haptoglobin plasma levels, although influenced by liver disease, are a sensitive index of intravascular hemolysis.
In addition to the various causes of decreased synthesis and increased consumption, low values of haptoglobin can be linked to increased losses. This condition occurs when the renal filter does not function properly and allows molecules normally retained in the blood to pass through; this is the case, for example, with the nephrotic syndrome. A similar argument can be made in the presence of protein-dispersing enteropathies.
A small percentage of the black and Asian population shows physiologically not measurable haptoglobin values.
Haptoglobin and sports
Endurance sports characterized by repeated microtraumas, such as running, cause repetitive traumatic damage that damages red blood cells during passage through the capillaries; they can therefore determine a significant reduction in haptoglobin levels.
Also in volleyball (impact of the ball on the hands) and bongos players, similar pictures were highlighted.
How to measure it
The haptoglobin test is performed by a simple blood test. The sample is taken from the vein of an arm.
Preparation
Blood is usually taken in the morning. To perform haptoglobin analysis, the patient must observe a fast of at least 8 hours, in which it is allowed to take only a modest amount of water.
Drugs that can increase haptoglobin levels include androgens and corticosteroids, while those that may decrease concentrations include isoniazid, quinidine, streptomycin and birth control pills.
Interpretation of Results
- A reduction of haptoglobin associated with an increase in the reticulocyte count and the low value of red blood cells may indicate the presence of anemia with intravascular hemolysis (in practice, the destruction of erythrocytes occurs in the circulation).
- When the value of haptoglobin is normal and the reticulocyte count is increased, however, the destruction of red blood cells could occur in organs such as the spleen and the liver (extravascular hemolysis; the released hemoglobin is not released into the bloodstream, hence the protein it is not consumed).
- If haptoglobin concentrations are normal and the reticulocyte count has not increased, then it is likely that the anemia present is not due to the breakdown of red blood cells.
- In the event that haptoglobin levels are decreased, without any other sign of haemolytic anemia, it is possible that the liver is not producing adequate amounts of the protein. This phenomenon can be observed in liver pathologies. Liver damage can inhibit both haptoglobin production and the removal of free protein-hemoglobin complexes.
- Interpretation of the results can be complicated in the presence of many inflammatory diseases (eg ulcerative colitis and acute rheumatic disease) or in case of heart attacks and serious infections. Hapoglobin concentrations can also be affected by massive blood loss and conditions associated with renal dysfunction.
