Congenital hypothyroidism (CH) is typically detected through the newborn screen. The newborn screen is performed with a collection of heel prick obtained blood sample on special filter paper. The newborn screen evaluates for several disorders in addition to congenital hypothyroidism. The timing of the newborn screen is very important and needs to be done after 24 hours of life. The reason for this is that there is a surge of thyroid stimulating hormone (TSH) that occurs shortly after birth. The elevation in TSH that occurs in the first 24 hours can falsely make the screen positive. Some states will also do a second screen between 10-14 days of life. There are established norms of TSH values that take this into account along with prematurity after the first day of life.
The newborn screen is crucial since most babies born with congenital hypothyroidism do not display any obvious signs or symptoms at birth or shortly after birth. If treatment is not initiated in a timely manner, the infant is at risk for developing sequelae of not having normal thyroid levels. These include abnormal weight gain and linear growth, jaundice, anemia, decreased tone, delayed milestones, and intellectual disability. All these can be avoided with timely diagnosis and initiation of treatment.
Which thyroid hormones does a newborn screen evaluate for? There are several different types of newborn screening methods. A newborn screen can evaluate and report TSH, total thyroxine, or both. This will depend on which state does the testing. Most states will screen with a TSH and secondarily report a T4 if the TSH is abnormal.
There will be a very small number of infants that will have a false negative on the newborn screen. This means the infant has the diagnosis but it was not detected by the screen. The following are risk factors that are associated with a false negative screen: preterm birth, low birth weight, same-sex twins, or family history of hypothyroidism.1 It would be advisable to obtain repeat thyroid function testing in these high risk infants.
What happens after your provider or medical team gets an alert for a positive screen from the state? Your provider or medical team will contact you and arrange for your baby to get bloodwork tests to confirm the newborn screen results or a second newborn is performed. In most places, there is a laboratory that is available that has a quick turnaround in results (within a day). If the repeat labs are consistent with congenital hypothyroidism then you will be contacted by the provider to start treatment right away. You will be counseled on the medication, how to take it properly, what to do when a dose is missed, what to avoid with giving the medications, and when to have blood work repeated to assess if the dose is adequate.
What happens if the test results are equivocal? Your infant will undergo follow-up testing until the labs normalize or a decision is made to initiate medication.
Your primary care team will most likely refer your infant to a pediatric endocrinologist who specializes in thyroid disorders.
For more information on newborn screening or congenital hypothyroidism:
The state of Colorado: https://cdphe.colorado.gov/laboratory-services/newborn-screening
The state of Florida: https://floridanewbornscreening.com/
1.Zhejiang Da Xue Xue Bao Yi Xue Ban 2022 Jun 25;51(3):314-320. doi: 10.3724/zdxbyxb-2022-0213.