The haptoglobin test measures the blood levels of haptoglobin. Haptoglobin is a protein that clears the free hemoglobin in the blood formed by red cell lysis. Haptoglobin is depleted in the presence of a large amount of hemoglobin. Hence, decreased amounts of haptoglobin in the blood is a marker of hemolysis. The reference range of haptoglobin in blood is 30-200 mg/dL. Spectrophotometry, gel electrophoresis, or immunoreactive methods can be used in the determination of haptoglobin levels in the blood.
Key areas Covered
Key Terms: Free Hemoglobin, Haptoglobin, Hemoglobin-Haptoglobin Complex, Hemolysis, Hemolytic Anemia
What is Haptoglobin
Haptoglobin is a protein, primarily produced by the liver and released into the bloodstream. The main function of haptoglobin is to bind with free hemoglobin in the blood. Two variants of haptoglobin can be found in the body known as Hp1-1, Hp1-2, and Hp2-2, which consist of variable binding capacities. Generally, hemoglobin occurs inside red blood cells. During hemolysis, free hemoglobin, which circulates in the blood, is produced. It scavenges free hemoglobin and forms hemoglobin-haptoglobin complex, which is degraded by the system. Hemoglobin-haptoglobin complex is shown in figure 1.
Free hemoglobin is responsible for vascular injury or dysfunction. It scavenges nitric oxide, a neurotransmitter that regulates smooth muscle relaxation, expression of endothelial adhesion molecules, platelet activation, and platelet aggregation. It also produces free radicals by reacting with hydrogen peroxide. Since free hemoglobin is hydrophobic, it disrupts lipid membranes. Haptoglobin prevents the accumulation of iron in the kidney.
What is Haptoglobin Test
Hemolysis may occur due to hemolytic anemia, malaria, and some infections. It results in free hemoglobin in the bloodstream. High levels of free hemoglobin in the blood cause depleted haptoglobin levels. Therefore, the determination of haptoglobin levels in the blood is critical in disease diagnosis. Haptoglobin test is performed when the symptoms of hemolytic anemia appear. These symptoms include
- Severe fatigue
- Pale skin
- Cold hands and feet
- Upper abdominal pain
- Shortness of breath
- Abnormal heartbeat
Some other conditions are involved in the reduced levels of haptoglobin in blood such as liver disease, seizure disorders, allergic conditions, malnutrition, after a surgery, and during pregnancy.
Venous blood is used in the haptoglobin test. Several methods such as the determination of peroxidase activity of hemoglobin-haptoglobin complex, spectrophotometry, immunoreactive methods, and gel electrophoresis are involved in the determination of haptoglobin in blood. The reference range of the haptoglobin test is 30-200 mg/dL.
- The low levels of haptoglobin indicate hemolytic anemia caused by the premature disruption of red blood cells. It may also indicate a reaction to blood transfusion, liver disease or infections.
- The higher levels of haptoglobin indicate inflammation, trauma, traumatic brain injury, tissue injury, and cancer.
Haptoglobin is a protein found in the blood, which is important in the clearance of free hemoglobin from the bloodstream. Free hemoglobin causes inflammation, oxidative-tissue damage, and kidney injury. Haptoglobin test measures the levels of haptoglobin in blood.
1. N, Biljana. “Haptoglobin: Test, High and Low Levels, and Associated Diseases.” Selfhacked, 14 Dec. 2017, .
1. “Hem-hap 4f4o” By Ayacop – Own work (CC0) via