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Haptoglobin is a protein produced by the liver and its main function is to bind and remove free hemoglobin from the bloodstream.
A haptoglobin test is an important diagnostic tool in detecting various medical conditions, including hemolytic anemia.
◉ What is a haptoglobin (HP) test?
Haptoglobin (Hp) is a blood protein produced by the liver, part of the inflammatory response proteins, whose levels increase in response to inflammation.
Its main function is to bind and remove free hemoglobin from the bloodstream by forming a haptoglobin-hemoglobin complex. This complex is then eliminated by the reticuloendothelial system.
In the case of hemolytic anemia, the Increased destruction of red blood cells leads to elevated hemoglobin release. This increases the formation of the haptoglobin-hemoglobin complex, leading to accelerated elimination. If this elimination exceeds the liver's capacity to produce haptoglobin, low levels will be detected in the blood.
The hemoglobin test is commonly requested in the presence of signs of hemolysis, inflammation, or to assess liver function.
◉ Functions of Hp
haptoglobin is a transport protein with three main phenotypes (Hp1-1, Hp2-1, Hp2-2). It has a half-life of 2 to 5 days and plays an essential role in
- Binding to hemoglobin: haptoglobin binds to free hemoglobin, released during intravascular hemolysis, to quickly form a high affinity complex called "haptoglobin-hemoglobin". This complex is eliminated in approximately 20 minutes, facilitating iron recovery and preventing complications associated with the release of free hemoglobin into the bloodstream.
- Possession of antioxidant activity.
- Exercise anti-inflammatory activity.
- Participation in angiogenesis and lymphangiogenesis.
◉ Why do I need a haptoglobin test?
A doctor may decide to perform a haptoglobin test in the following situations
1. Symptoms of anemia
- Fatigue
- Pale skin
- Jaundice, or yellowing of the skin and sclera
- Upper abdominal pain
- Shortness of breath
- Rapid heart rate
- Dizziness
- Lightheadedness
- Cold hands and feet
2. Symptoms of liver damage
- Pain or swelling in the abdomen.
- Persistent jaundice.
- Severe itchy skin.
- Dark urine.
- Discolored stools.
3. When there are signs of inflammation
- Persistent fever
- Swelling of the joints
- Redness or warmth on the skin
- Other non-specific inflammatory signs
◉ Preparation for the test
A haptoglobin test typically does not require any special preparation beforehand. However, it is important to discuss your medical history and medications with your doctor before undergoing a haptoglobin test.
You should know that test results can be affected by a variety of conditions, such as:
- Rheumatoid arthritis.
- Chronic liver disease.
- Ulcerative colitis.
Also, some medications can impact the result of the test including:
- Corticosteroids.
- Birth control pills.
This information can help ensure that the test results are interpreted accurately and in the context of your overall health.
◉ Haptoglobin Normal Level
The normal levels of haptoglobin are as follows:
- Adult: 50 - 220 mg/dL or 0.5 - 2.2 g/L (SI units).
- Newborn: 0 - 10 mg/dL or 0 - 0.1 g/L (SI units)
The drop in haptoglobin level below 45 mg/dL may mean that your red blood cells are destroyed more quickly than their formation rate.
◉ Low Haptoglobin Levels
A low haptoglobin level refers to a situation where the concentration of haptoglobin protein in the blood is lower than the normal range.
◉ Causes of Low Haptoglobin Levels
Low levels of haptoglobin are seen in the following conditions:
- Intravascular hemolysis (hereditary spherocytosis, autoimmune hemolytic anemia, transfusion reactions).
- Extravascular hemolysis (intraperitoneal hemorrhage).
- Intramedullary hemolysis (thalassemia, megaloblastic anemia, sideroblastic anemia).
- Cirrhosis.
- Infancy.
- Pregnancy.
- Burns.
- Drugs, such as birth control pills, chlorpromazine, diphenhydramine, indomethacin, isoniazid, quinidine, streptomycin, and nitrofurantoin.
- Genetics.
◉ Symptoms of Low Haptoglobin Levels
Low haptoglobin levels usually don't directly cause specific symptoms. Instead, the symptoms you have are often linked to the underlying condition or illness causing the drop in haptoglobin.
◉ High Haptoglobin Levels
A high haptoglobin level refers to a situation where the concentration of haptoglobin protein in the blood is higher than the normal range.
◉ Causes of High Haptoglobin Levels
Haptoglobin is an acute-phase marker of red blood cell destruction. High levels of haptoglobin are seen in the following conditions:
- Diseases associated with elevation of erythrocyte sedimentation rate (ESR), such as infection, inflammation, hepatitis, collagen diseases, lymphoma, and leukemia.
- Obstructive or biliary diseases.
- Aplastic anemia.
- Nephrotic syndrome.
- Diabetes mellitus
- Increased estrogen level.
- Smoking.
- Steroid use.
- Androgens.
Symptoms of high levels of haptoglobin may differ according to the disorder causing these high levels.
◉ Additional test
Your doctor may order other blood tests to make a diagnosis. These tests may include:
◉ Hemolysis assessment
- Reticulocyte count: measures the number of reticulocytes in the blood. If the number is too high or too low, it may indicate health problems, including anemia and bone marrow disorders.
- Hemoglobin: it measures the hemoglobin level in the blood. It helps detect various blood disorders. It could be ordered as part of a complete blood count (CBC).
- Hematocrit test: it measures the quantity of red blood cells in the blood. Abnormal levels could mean the presence of a blood disorder.
- Blood smear: A blood sample is spread on a glass slide and treated with a special dye. It can detect abnormal red blood cells.
- LDH (Lactate Dehydrogenase): cytoplasmic enzyme that plays a role in energy production. Elevated LDH may be seen in hemolytic or pernicious anemia.
- Hemopexin (HPX): Heme-binding protein, its level can vary in the event of hemolysis.
- Free bilirubin: Measurement of unconjugated bilirubin, often increased in cases of hemolysis.
◉ Assessment of inflammation
- CRP (C-reactive protein): General indicator of inflammation.
- Sedimentation rate: Measurement of the speed at which red blood cells settle at the bottom of a tube, increasing in the event of inflammation.
- Fibrinogen: Protein involved in blood clotting, its level can increase in response to inflammation.
- Orosomucoid: Increases during inflammation, but not during hemolysis.
◉ Evaluation of liver function
- ALT (Alanine Aminotransferase)
- AST (Aspartate Aminotransferase)
- Alpha2 Macroglobulin
- HGF (Hepatocyte Growth Factor)
- Viral serology
◉ Conclusion
The haptoglobin test is an important test in order to diagnose many medical conditions, including hemolytic anemia.
This test doesn't require any special preparation but you should tell your doctor about your medical history and medicines that you take, as some diseases and medicines can affect the accuracy of the results.