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Infectious Diseases

What Parents Need to Know About Newborn Screenings

Babies can look healthy at birth and still have a serious health condition, which is why newborn screening tests are completed before discharge from the hospital.

Doctors test a few drops of blood, taken from a baby’s heel, for a number of disorders, including a potentially fatal disorder of the immune system known as severe combined immunodeficiency (SCID).

The immune system comprises cells in the body that protect it from infection. SCID is a disorder where the immune system is so weak that any infection, even a common cold, can be life-threatening. Many people remember David Vetter, who was born with SCID and became affectionately known as the “boy in the bubble.” 

The good news is SCID can be successfully treated if diagnosed early before serious infections develop. Dr. John Routes, professor of pediatrics at the Medical College of Wisconsin, was the senior investigator for the first statewide program to screen all newborns for SCID. By 2018 (a decade later), all 50 states had implemented SCID screenings.

Dr. John Routes

Professor of Pediatrics, Medical College of Wisconsin

What is newborn screening (NBS) and when does it take place?

NBS is a simple blood test that is performed to check for a variety of disorders that are not apparent after delivery. The test is usually done by heel prick approximately 24-48 hours after birth and before the baby leaves the hospital.

Do parents have to consent to the screening?

Most states require mandatory newborn screening. Only Wyoming requires parental consent for NBS. The majority of states require the parents to be informed about newborn screening and may permit parents to opt-out for certain reasons, such as religious objections.   

What do doctors test during the screening? What other health conditions would cause an abnormal result?

Each state decides what disorders to screen for, but most states test for the disorders recommended by the Health Resources and Services Administration in its Recommended Uniform Screening Panel

NBS tests for disorders of metabolism (e.g., phenylketonuria-PKU), hormones (e.g., hypothyroidism), hemoglobin (e.g., sickle cell disease), and other rare but serious diseases, such as severe combined immunodeficiency (SCID) and cystic fibrosis. Many states also screen for hearing loss and serious congenital heart disease, which blood tests do not screen for.

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What is the name of the particular kind of test used to identify SCID and what kind of results would indicate SCID may be present?

The NBS test used to screen for SCID is the TREC (T cell receptor excision circle) test. TRECs are made when the immune system makes new T cells. 

T cells are very low or absent in people who have SCID. Therefore, a low number of TRECS are found in babies with SCID or other conditions associated with low numbers of T cells. 

 Please discuss false-positives in the screenings. Are they common?

Sometimes an NBS test will be positive for a disorder but follow-up testing will show the baby does not have the disease — this is called a false-positive test. False-positive results are not uncommon and the percentage of false-positive results may vary from state to state depending on the specific disorders tested for.

The disorders NBS tests detect are serious and treatable. Therefore, it is very important to identify as many babies as possible, which sometimes leads to a false-positive test result.

To read the full interview, visit primaryimmune.org/scid-compass/NBSQ&A.

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