Many people carrying the sickle cell trait do not know that they have it. As a result, most states routinely screen all newborns for the disease. Screening is available by request in all other states. These tests reveal whether the infant has the disease or carries sickle cell trait. Diagnosis of the disease in infants is important because it ensures that the babies receive necessary treatment immediately.

Older children and adults can also be screened for sickle cell anemia and sickle cell trait. In adults, the required blood sample is usually drawn from a vein in the arm. In babies and young children, blood may be collected from a finger or heel prick. It is also possible to detect sickle cell anemia before birth by testing a sample of amniotic fluid (the fluid surrounding the fetus in the uterus) or tissue collected from the placenta.

The sickle cell test is a blood test used to determine whether a patient has the abnormal hemoglobin that causes sickle cell anemia (hemoglobin S) in their blood. A deoxygenation agent is added to the blood sample. When 25 percent or more of the hemoglobin is hemoglobin S, the red blood cells will structurally change into a sickle (crescent) shape. This occurrence indicates that the patient either has sickle cell anemia or has sickle cell trait.

In order to determine whether a patient has the disease or just carries the defective gene, the percentage of hemoglobin S in the blood has to be measured. Patients with sickle cell trait will have a small percentage of hemoglobin S in the blood, whereas people with sickle cell anemia will have a significantly larger percentage of the abnormal hemoglobin.   

To determine what types of hemoglobin are present in the blood, physicians will order a hemoglobin electrophoresis. During this test, electrical charges are sent through a solution of hemoglobin. Because different types of hemoglobin move different distances in response to an electric charge, the test can be used to differentiate normal hemoglobin (hemoglobin A) from hemoglobin S. Patients with significant levels of abnormal hemoglobin S may be diagnosed with sickle cell anemia in this manner.

Patients diagnosed with sickle cell anemia will be tested for anemia. A complete blood count will be ordered to determine the number of red blood cells in the blood. A number of additional tests may be ordered to check for other potential complications of the disease.

Children and adults with the disease may be referred to a hematologist, a physician who specializes in blood diseases. Carriers of sickle cell trait may be referred to a genetic counselor, a professional who specializes in genetic diseases. Such counselors can provide a carrier with information regarding their risk of having a child with sickle cell anemia. They can also explain treatment options, preventive measures and reproductive choices.