• Dr. Princenton Ly, MD
  • Jul 05, 23
  • 5 min read

87. What You Need To Know About Newborn Screening Tests – Dr. Princeton Ly, MD

"Your pediatrician will continue (usually after the infant stage) to test your child's hearing as he/she gets older. As always - if you're ever worried about your baby's hearing - ask your pediatrician for more advice on what to look for / what to expect / what to do next!"

What is newborn screening?

Newborn screening tests identify conditions that can be life-threatening, so we can intervene early and prevent serious consequences like death and disability. They are minimally invasive and help “rule out” a lot of possibly hidden concerns that could otherwise go undetected. They are typically all performed on the baby in the hospital after the first 24 hours or so of life, and are generally required (if not strongly recommended) to be completed prior to discharge from the birth hospitalization (note: the below applies to all healthy babies in the newborn nursery but if you have a baby in the NICU only some components might apply / timing may vary.) There are three main components to newborn screening in the United States, outlined below in detail.

Critical Congenital Heart Disease Screening

This test looks for serious heart conditions that sometimes do not immediately show up with signs or symptoms. These conditions can show up even without any family history, despite the presence of good prenatal care, and an otherwise normal examination of the baby. The test is quite simple – two non-invasive (read: no needles) oxygen monitors are placed on the baby for several minutes – typically the right hand and the right foot. If the oxygen level reading is normal and matching between the two extremities – the test is ‘passed’. If not – the test may be repeated to confirm a ‘failed’ screening and then your doctors (including your pediatrician / NICU team / pediatric cardiologists) may get involved for next steps which typically include an echocardiogram, or an ultrasound of the heart and its blood vessels. Fear not though – true ‘failed’ screening tests are somewhat rare – found in <1% of babies.

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Hearing Screen

This test looks for babies who have hidden hearing loss – something that happens in ~3 of 1000 babies. When identified (which usually requires confirmatory testing outside of the hospital / after discharge with a hearing specialist called an audiologist), the baby will then be referred ASAP to centers where early intervention and treatment can happen to maximize communication and language (and academic and socioemotional) development.

There are two types of hearing screen methods – both of which can be completed in a matter of minutes while baby is asleep or otherwise still. One is called an “Automated Auditory Brainstem Response”, or AABR – that measures how the brain and hearing nerve respond to sound. Soft earphones are placed into the baby’s ear in this method and then clicks and tones are played. Electrodes placed on the baby’s head (again, non-invasive / no needles!) will record the response. Another is called an “Otoacoustic Emissions” (OAE) which measures sound waves made by the inner ear. This test involves a probe placed in the baby’s ear canal (no needles!) that measures the response when clicks/tones are played. Your birth hospital typically will choose one of these tests to perform routinely – you do not have to choose. In addition, the tests are both accurate/valid – one is not better than the other.

One last note: this test is not perfect and there are other ways hearing loss can present (like after ear trauma or an infection; other causes may include progressive hearing loss disorders that show up in later life/childhood). Your pediatrician will continue (usually after the infant stage) to test your child’s hearing as he/she gets older. As always – if you’re ever worried about your baby’s hearing – ask your pediatrician for more advice on what to look for / what to expect / what to do next!


Genetic Screening

Also confusingly referred to as just “newborn screening” (older parlance might include the “PKU” test, named after the first test it included – phenylketonuria), this test does involve a needle. A heel prick is used to get some drops of baby’s blood, which are then put on a special paper. This is then sent to the state lab for testing. Things tested include conditions you may have heard about – like hypothyroidism, cystic fibrosis, and sickle cell disease – and many you may have not- like biotinidase deficiency and spinal muscular atrophy. Most of these disorders are rare, but all are treatable in some form if caught early. California now tests for over 80 disorders (full list here). The results, if positive, are communicated in an expedient fashion to you, the parents – as well as your pediatrician of record and specialists (sometimes including a geneticist). Confirmatory testing is usually required as a next step. If negative – your pediatrician should receive a letter confirming all is well. Most “newborn screens” are normal / negative!

Other Screening Tests

Your hospital team / pediatrician may mention other tests that need to be done prior to discharge, like:

– Bilirubin / jaundice testing: This is a topic all its own, but involves either a noninvasive skin probe or a heel prick to test for a chemical the body naturally makes as it breaks down / recycles red blood cells called bilirubin. This compound commonly builds up to high levels in newborns, and at extremely high levels can cause brain damage. Testing/management of bilirubin is a complicated subject – your pediatrician / hospital team should help you navigate this. All babies should get at least one bilirubin test prior to going home.

– Car seat test (also sometimes referred to as a car seat challenge or car seat safety test): This is reserved only for infants that are born early or prematurely – before 37 weeks, and reassures everyone that baby can tolerate the ride home safely. It involves placing your child into the car seat you will take him/her home in and placing monitors to look for changes in heart rate, breathing and oxygen level. If everything is normal for a predetermined period of time – 90-120 minutes commonly – the baby has passed! If at any point the vital signs are abnormal – your baby will be taken out of the car seat and his/her doctors notified so next steps in evaluation/treatment can be discussed.

To Conclude

Newborn screening tests are crucial in keeping our children healthy. By anticipating hearing, heart, and genetic issues we can intervene early and institute effective interventions. It is my strong recommendation that your child (and all children) receive, and hopefully pass, these minimally invasive tests in their first days of life. If you have any questions, as always – please touch base with your pediatrician!


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Dr. Princeton Ly is a board-certified pediatrician and fellow of the American Academy of Pediatrics, who practices in Santa Monica. He sees children of all ages, from newborns to teenagers. Dr. Ly’s professional interests include: parenting guidance, preventative care, evidence-based medicine, and student mentorship. Dr. Ly completed his undergraduate degree at UCLA before attending medical school at the University of Hawaii. He returned to UCLA for residency training (including specializations in primary care and public health), and then joined UCLA Santa Monica Pediatrics in 2019. Alongside being a True Bruin, Dr. Ly is a dedicated Angeleno – born and raised between Whittier and San Marino in Southern California. In his spare time, he enjoys traveling, rooting for the local teams (UCLA, Dodgers, Lakers), and exploring the Los Angeles food scene with his wife, two daughters, and their puppy. Learn more about Dr. Ly and his clinic here and here.