A sickle cell test is a simple blood test used to determine if you have sickle cell disease (SCD) or sickle cell trait. People with SCD have red blood cells (RBCs) that are abnormally shaped. Sickle cells are shaped like a crescent moon. Normal RBCs look like doughnuts.

The sickle cell test is part of routine screening performed on a baby after they’re born. However, it can be used on older children and adults when needed.

SCD is a group of inherited RBC disorders. The disease is named for the C-shaped farming tool known as a sickle.

Sickle cells often become hard and sticky. This can increase the risk of blood clots. They also tend to die off early. This causes a constant shortage of RBCs.

SCD causes the following symptoms:

Sickle cell trait

People with sickle cell trait are genetic carriers of SCD. They have no symptoms and can’t develop SCD, but they may be able to pass it on to their children.

Those with the trait may have a higher risk of some other complications, including unexpected exercise-related death.

Newborns are regularly screened for SCD soon after birth. Early diagnosis is key. This is because children with SCD may be more vulnerable to serious infections within weeks of birth. Testing early helps ensure infants with SCD get the proper treatment to protect their health.

Other people who should get tested include:

  • immigrants who haven’t been tested in their home countries
  • children who move from one state to another and haven’t been tested
  • anyone displaying symptoms of the disease

SCD affects approximately 100,000 Americans and millions of people worldwide, estimates the Centers for Disease Control and Prevention.

No preparation is required for the sickle cell test. However, receiving a sickle cell test within 90 days after a blood transfusion may lead to inaccurate test results.

Transfusion can reduce the amount of hemoglobin S — the protein that causes SCD — in the blood. A person who’s undergone a recent transfusion may have a normal sickle cell test result, even if they have SCD.

Your doctor will need a blood sample to test for SCD.

A nurse or lab technician will place an elastic band around your upper arm to make the vein swell with blood. Then, they’ll gently insert a needle into the vein. The blood will naturally flow into the tube attached to the needle.

When there’s enough blood for the test, the nurse or lab tech will take the needle out and cover the puncture wound with a bandage.

When infants or very young children are tested, the nurse or lab tech may use a sharp tool called a lancet to puncture skin on the heel or finger. They’ll collect the blood on a slide or test strip.

The sickle cell test is a normal blood test. Complications are extremely rare. You may feel a little lightheaded or dizzy after the test, but these symptoms will go away when you sit down for a few minutes. Eating a snack may also help.

The puncture wound has a slim chance of becoming infected, but the alcohol swab used prior to the test normally prevents this. Apply a warm compress to the site if you develop a bruise.

The lab tech who examines your blood sample will be looking for an abnormal form of hemoglobin called hemoglobin S. Regular hemoglobin is a protein carried by RBCs. It picks up oxygen in the lungs and delivers it to other tissues and organs throughout your body.

Like all proteins, the “blueprint” for hemoglobin exists in your DNA. This is the material that makes up your genes. If one of the genes is altered or mutated, it can change how the hemoglobin behaves. Such mutated or abnormal hemoglobin can create RBCs that are sickle-shaped, leading to SCD.

A sickle cell test looks only for the presence of hemoglobin S, which causes SCD. A negative test is normal. It means your hemoglobin is normal. A positive test result may mean you have sickle cell trait or SCD.

If the test is positive, your doctor will probably order a second test called hemoglobin electrophoresis. This will help determine which condition you have.

If the test shows you have two abnormal hemoglobin genes, your doctor will likely make an SCD diagnosis. If the test shows you have only one of these abnormal genes and no symptoms, your doctor will likely make the diagnosis of sickle cell trait.

After the test, you’ll be able to drive yourself home and perform all of your normal daily activities.

Your doctor or lab tech can tell you when to expect your test results. Since newborn screenings vary by each state, results may take up to two weeks for infants. For adults, it may be as fast as one business day.

Your doctor will go over your test results with you. If the test shows you have the sickle cell trait, they may order more tests before they confirm a diagnosis.

If you receive a diagnosis of SCD, your doctor will work with you to develop a treatment plan that works for you.