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Sickle cell test

Definition

A sickle cell test looks for the presence or absence of abnormal hemoglobin in the blood that causes sickle cell anemia.

Alternative Names

Sickledex; Hgb S test

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

This test is done to tell if you have abnormal hemoglobin that causes sickle cell disease and sickle cell trait.

In sickle cell disease, a person has two abnormal hemoglobin S genes.

A person with sickle cell trait has only one of the problem hemoglobin S genes and no symptoms, or only mild ones.

However, this test does not tell the difference between these two conditions. Another test called hemoglobin electrophoresis is needed to do so.

Normal Values

A negative test result is normal.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

• Sickle cell anemia
• Sickle cell trait

What the risks are

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Special considerations

Iron deficiency or blood transfusions within the past 3 months can cause a false negative result.

References

Saunthararajah Y, Vichinsky EP, Embury SH. Sickle cell disease. In: Hoffman R, Benz EJ Jr, Shattil SJ, Furie B, Cohen HJ, eds. Hematology: Basic Principles and Practice. 4th ed. Philadelphia, Pa: Churchill Livingston; 2005:chap 37.