Sickle cell test

Definition

The sickle cell test looks for the abnormal hemoglobin in the blood that causes the disorder sickle cell disease.

Alternative Names

Sickledex; Hgb S test

How the Test is Performed

A blood sample is needed.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a bruise. This soon goes away.

Why the Test is Performed

This test is done to tell if a person has hemoglobin S which is the abnormal hemoglobin that causes sickle cell disease and sickle cell trait. Hemoglobin is a protein in red blood cells that carries oxygen.

People with sickle cell disease have two abnormal hemoglobin S genes. A person with sickle cell trait has only one of these abnormal genes and no symptoms, or only mild ones.

This test does not tell the difference between these two conditions. Another test, called hemoglobin electrophoresis, will be done to tell which condition someone has.

Normal Results

A normal test result is called a negative result meaning that there is no hemoglobin S.

Normal value ranges may vary slightly among different labs. Some labs use different measurements or test different samples. Talk to your health care provider about the meaning of your specific test results.

What Abnormal Results Mean

An abnormal test result indicates the person might have one of these:

• Sickle cell disease
• Sickle cell trait

Iron deficiency or blood transfusions within the past 3 months can cause a false negative result. This means the person might have the abnormal hemoglobin for sickle cell but these other factors are making their test results appear negative (normal).

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person 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 lightheaded
• Multiple punctures to locate veins
• Hematoma (blood buildup under the skin)
• Infection (a slight risk any time the skin is broken)

References

Centers for Disease Control and Prevention website. Get screened to know your sickle cell status. www.cdc.gov/sickle-cell/sickle-cell-trait/fact-sheet-get-screened-to-know-your-sickle-cell-status.html. Updated May 15, 2024. Accessed April 10, 2026.

Centers for Disease Control and Prevention website. Sickle Cell Disease (SCD). About sickle cell disease. www.cdc.gov/sickle-cell/about/index.html. Updated February 21, 2025. Accessed April 10, 2026.

Menapace LA, Thein SL. Clinical aspects of sickle cell disease. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 43.

Smith-Whitley K, Kwiatkowski JL. Hemoglobinopathies. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 511.