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Hemoglobin S

Does this test have other names?

Hgb S test, sickle cell test, Sickledex

What is this test?

This test looks for an abnormal type of hemoglobin called hemoglobin S in your blood.

Hemoglobin is the main part of your red blood cells. It carries oxygen through your blood. If your hemoglobin level is too low, you may not be able to supply the cells in your body with the oxygen they need to survive. Hemoglobin S (Hgb S) is an abnormal type of hemoglobin that you can inherit from your parents.

Hgb S causes red blood cells to become stiff and abnormally shaped. Instead of having a normal round, disk shape, these red blood cells become sickle-shaped, or crescent-shaped. They don't live as long as normal red blood cells, and they get stuck inside small blood vessels. These problems cause symptoms of sickle cell disease.

If you or your child inherits one normal hemoglobin gene and one Hgb S gene, it's called having sickle cell trait. If the Hgb S gene is inherited from both parents, the person has sickle cell disease.

Why do I need this test?

You may need this test if you have symptoms of sickle cell disease or if you are being screened to see if you carry the Hgb S gene. Symptoms of sickle cell disease may include:

  • Being short of breath

  • Having cold, pale skin, especially the hands and feet

  • Headaches or dizziness

  • Jaundice, or yellowed skin or eyes

Your child may need this test as part of a newborn screening.

What other tests might I have along with this test?

Your doctor may also order other blood tests to check for anemia. He or she may also order a test called hemoglobin electrophoresis to help find out the amounts of different hemoglobin types in your blood. This test helps figure out if you have sickle cell trait or sickle cell disease.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normal results are negative, meaning no sickle cells were seen. Positive results mean sickle cells were seen. Your doctor will confirm these results with hemoglobin electrophoresis.

Here is what other test results may mean:

  • If Hgb S makes up 20 to 40 percent of hemoglobin, you have sickle cell trait. People with sickle cell trait don't usually have symptoms of sickle cell disease.

  • If Hgb S makes up 80 to 100 percent of hemoglobin, you have sickle cell disease.

A positive result may also mean that you have another blood disease like pernicious anemia or polycythemia, or that you've had a recent blood transfusion.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

In small children or infants, blood can be taken by a skin prick.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Certain medications can affect your results, as can having the test too soon after a blood transfusion. (The test shouldn't be used for up to four months after a transfusion.)

In children, age can affect results. Children younger than 3 months may have normal results but still develop sickle cells by age 6 months.

How do I get ready for this test?

You don't have to prepare for this test. Make sure to tell your doctor about any blood transfusion you may have had in the past. In addition, be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.