Haptoglobin

Also Known As:
HPT
Hemoglobin-binding Protein
Hp

This article was last modified on September 18, 2020

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Anemia Testing

At a Glance

Why Get Tested?

To help detect and evaluate hemolytic anemia

When To Get Tested?

When you have signs of anemia such as weakness, paleness, or jaundice, which is yellowing of the skin and whites of the eyes, that a healthcare practitioner suspects may be due to red blood cell destruction (hemolytic anemia)

Sample Required?

A blood sample drawn from a vein

Test Preparation Needed?

None

Looking For Test Results?

Looking For Reference Ranges?

You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Testing.com. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Testing.com is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

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 by the liver so that it can be broken down and the iron recycled. Formation of the haptoglobin-hemoglobin complex also prevents hemoglobin from being filtered by the kidneys and passed into the urine, which can be toxic to the kidneys.

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 levels 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 you have a condition that is causing red blood cells to be destroyed or to break apart. When the binding capacity of haptoglobin is exceeded, the free hemoglobin level in circulation goes up and may cause tissue damage and/or organ dysfunction due to oxidative stress of free hemoglobin.

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 yellowed, also called jaundice.

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

Common Questions

How is the test used?

Haptoglobin testing is used primarily to help detect and evaluate hemolytic anemia and to distinguish it from anemia due to other causes. Testing is used to help determine whether red blood cells (RBCs) are breaking apart or being destroyed prematurely. It may be used in conjunction with other laboratory tests such as a complete blood count (CBC, including RBC count, hemoglobin, hematocrit), reticulocyte count, lactate dehydrogenase, bilirubin, direct antiglobulin test, and blood smear.

Though the haptoglobin test is a sensitive test for hemolytic anemia, it cannot be used to diagnose the cause of the condition. Other laboratory tests may be needed to help determine the cause, such as tests for autoantibodies to detect autoimmune causes, sickle cell tests, G6PD, or a hemoglobin evaluation.

If you have had a blood transfusion, a haptoglobin test may be ordered along with a direct antiglobulin test to help determine if you have had a transfusion reaction. (For more details, see the article on Transfusion Medicine.)

If your haptoglobin level is low, then testing may be repeated at a later time to monitor your condition, evaluate changes in concentration, and help determine whether the increased destruction of RBCs persists.

When is it ordered?

The haptoglobin test is ordered when you have symptoms and signs associated with hemolytic anemia. Some examples include:

Fatigue, weakness
Pale skin (pallor)
Fainting
Shortness of breath
A rapid heart rate
Jaundice, yellowing of the skin and whites of the eyes
Red or brown urine (from the presence of blood/hemoglobin)

Testing may also be done when other laboratory test results are consistent with hemolytic anemia. These may show increased bilirubin, hemoglobin in the urine (hemoglobinuria), decreased RBC count, and increased reticulocyte count and lactate dehydrogenase levels.

What does the test result mean?

Results are interpreted carefully and in conjunction with results of other tests, such as a reticulocyte count, red blood cell (RBC) count, hemoglobin (Hb), hematocrit (Hct), or complete blood count (CBC).

When your haptoglobin level is significantly decreased, along with an increased reticulocyte count and a decreased RBC count, hemoglobin, and hematocrit, then it is likely that you have some degree of hemolytic anemia with red blood cells destroyed in the circulation (intravascular hemolysis).

If your haptoglobin level is normal or borderline normal and your reticulocyte count is increased, then RBC destruction is likely occurring in organs such as the spleen and liver (extravascular hemolysis). Because the free hemoglobin is not released into the blood, the haptoglobin is not used up and remains at a normal level. However, in severe extravascular hemolysis, haptoglobin level can be low because excess hemolysis can release some free hemoglobin into circulation.

If your haptoglobin level is normal and the reticulocyte count is not increased, then it is likely that your anemia is not due to RBC breakdown but due to some other cause.

The following table summarizes some results that may be seen:

Haptoglobin	Reticulocyte count	RBC count, Hemoglobin, Hematocrit	Possible interpretation
Significantly decreased	Increased	Decreased	RBCs are being destroyed within blood vessels (intravascular hemolysis)
Normal or slightly decreased	Increased	Decreased	RBCs destruction likely within organs such as the spleen and liver (extravascular hemolysis)
Normal	Not increased	Decreased	Anemia due to a cause other than RBC destruction (e.g., decrease in RBC production in the bone marrow)

If haptoglobin is decreased without any signs of hemolytic anemia, then it is possible that the liver is not producing adequate amounts of haptoglobin. This may be seen with liver disease, although haptoglobin is not typically used to diagnose or monitor liver disease.

Is there anything else I should know?

Congenital haptoglobin deficiency (called “anhaptoglobinemia” that is unrelated to hemolysis or liver disease) is also seen in the general population, affecting about 0.1% of Caucasians and 4% of African Americans (up to 30% in Africans of certain West African origin). Your healthcare provider may order additional tests (e.g., hemopexin test) to help determine if low haptoglobin is congenital or is related to RBC hemolysis.

A low level of haptoglobin is normal for newborns and infants less than 6 months old.

What conditions or other factors can affect haptoglobin levels?

Haptoglobin is considered an “acute-phase” protein. This means that it will be elevated in many inflammatory diseases, such as ulcerative colitis, acute rheumatic disease, heart attack, and severe infection. If you have one of these conditions, it can complicate the interpretation of the haptoglobin results. Haptoglobin testing is not generally used to help diagnose or monitor these conditions.

Haptoglobin levels may be affected by massive blood loss and by conditions associated with kidney dysfunction as well as liver disease.

Drugs that can increase haptoglobin levels include androgens and corticosteroids. Drugs that can decrease haptoglobin concentrations include isoniazid, quinidine, streptomycin, and birth control pills.

If my haptoglobin level is low, when will it return to normal?

It depends on the cause of the low level. If it is due to acute hemolysis, such as may be seen with a transfusion reaction, then it will return to normal once the reaction resolves. If it is due to chronic hemolysis, then the level should return to normal if and when the underlying condition can be resolved. If the underlying condition cannot be resolved or if the decreased level of haptoglobin is due to decreased production due to liver disease, then the level may continue to be lower than normal.

Can I have the haptoglobin test done in my healthcare practitioner's office?

In most cases, no. This test is typically either performed in a hospital laboratory or sent to a reference laboratory.

Is a haptoglobin test used for anything else?

The haptoglobin test may be also ordered inside the laboratory to differentiate between a hemolyzed specimen due to RBCs’ destruction inside the body from a hemolyzed specimen due RBCs’ destruction after a blood draw. However, few studies have been found that support this use.

View Sources

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