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Also known as: HPT; Hemoglobin-binding Protein; Hp
Formal name: Haptoglobin

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The Test Sample

What is being tested?

Haptoglobin is a protein produced by the liver that the body uses to clear free hemoglobin (found outside of red blood cells) from circulation. This test measures the amount of haptoglobin in the blood.

Hemoglobin is the iron-containing protein complex that transports oxygen throughout the body. It is normally found within red blood cells (RBCs) and very little is found free circulating in the blood. Haptoglobin binds to free hemoglobin in the blood. This forms a haptoglobin-hemoglobin complex that is rapidly cleared out of circulation for degradation and iron recycling.

However, when an increased number of RBCs are damaged and/or break apart (hemolysis), they release their hemoglobin into the blood, increasing the amount of free hemoglobin in circulation. When large numbers of RBCs are destroyed, haptoglobin concentrations in the blood will temporarily decrease as the haptoglobin is used up faster than the liver can produce it. A decrease in the amount of haptoglobin may be a sign that a person has a condition that is causing red blood cells to be destroyed or break apart. When the binding capacity of haptoglobin is exceeded, free hemoglobin level in circulation goes up and may cause tissue damage and organ dysfunction.

Increased RBC destruction may be due to inherited or acquired conditions. Some examples include transfusion reactions, certain drugs, and mechanical breakage, such as may be seen with some prosthetic heart valves. The destruction may be mild or severe, occurring suddenly (acute) or developing and lasting over a long period of time (chronic), and it can lead to hemolytic anemia. People with hemolytic anemia may experience symptoms such as fatigue, weakness, and shortness of breath and their skin may be pale or jaundiced. (For additional details, read the article on Hemolytic Anemia.)

Liver disease may also result in decreased haptoglobin concentrations as liver damage may inhibit both the production of haptoglobin and the clearing of the haptoglobin-free hemoglobin complexes.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.