A blood test can check for hemoglobin S — the defective form of hemoglobin that underlies sickle cell anemia. In the United States, this blood test is part of routine newborn screening done at the hospital. But older children and adults can be tested, too.
In adults, a blood sample is drawn from a vein in the arm. In young children and babies, the blood sample is usually collected from a finger or heel. The sample is then sent to a laboratory, where it's screened for hemoglobin S.
If the screening test is negative, there is no sickle cell gene present. If the screening test is positive, further tests will be done to determine whether one or two sickle cell genes are present. People who have one gene — sickle cell trait — have a fairly small percentage of hemoglobin S. People with two genes — sickle cell disease — have a much larger percentage of the defective hemoglobin.
To confirm any diagnosis, a sample of blood is examined under a microscope to check for large numbers of sickle cells — a marker of the disease. If you or your child has the disease, a blood test to check for anemia — a low red blood cell count — will be done. And your doctor may suggest additional tests to check for possible complications of the disease.
If you or your child carries the sickle cell gene, you may be referred to a genetic counselor — an expert in genetic diseases.
Tests to detect sickle cell genes before birth
Sickle cell anemia can be diagnosed in an unborn baby by sampling some of the fluid surrounding the baby in the mother's womb (amniotic fluid) to look for the sickle cell gene. If you or your partner has been diagnosed with sickle cell anemia or sickle cell trait, ask your doctor about whether you should consider this screening. Ask for a referral to a genetic counselor who can help you understand the risk to your baby.
Mar. 26, 2011
- Saunthararajah Y, et al. Sickle cell disease: Clinical features and management. In: Hoffman R, et al. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa.: Churchill Livingstone Elsevier; 2009. http://www.mdconsult.com/books/about.do?about=true&eid=4-u1.0-B978-0-443-06715-0..X5001-8--TOP&isbn=978-0-443-06715-0&uniqId=230100505-56. Accessed Jan. 24, 2011.
- Rees DC, et al. Sickle-cell disease. The Lancet. 2010;376:2018.
- Sickle cell anemia. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/Sca/SCA_All.html. Accessed Jan. 24, 2011.