All newborns should be screened for congenital hypothyroidism within 48 to 72 hours of birth, and prompt treatment after diagnosis is necessary to avoid adverse outcomes, according to a report from the American Academy of Pediatrics.
A new guideline published in Pediatrics outlines the steps providers should take for screening and treating congenital hypothyroidism among newborns. Among the recommendations, the authors argue for universal congenital hypothyroidism screening for newborns. According to the authors, about 70% of newborns globally do not undergo screening, and newborn screening for congenital hypothyroidism is not established in some countries.
“Missing the diagnosis of congenital hypothyroidism in a newborn infant will lead to permanent intellectual disability,” Susan R. Rose, MD, FAAP, professor emerita of pediatric endocrinology at Cincinnati Children’s Hospital Medical Center and the University of Cincinnati College of Medicine, told Healio. “Newborn screening for congenital hypothyroidism and other disorders should be performed on all infants both in the U.S. and globally.”
Screening, treating congenital hypothyroidism
To screen for congenital hypothyroidism, a dried blood spot should be obtained by heel stick on an approved filter paper card. Screening should take place within 48 to 72 hours of birth. The authors noted that screening too early may lead to false-positive results. Three test strategies are typically used to screen for congenital hypothyroidism: primary thyroid-stimulating hormone and reflex thyroxine; primary T4 and reflex TSH, or a combined T4 and TSH measurement. All three strategies can detect congenital hypothyroidism with similar accuracy.
Susan Rose
“Congenital hypothyroidism should be treated as soon as possible after the diagnosis is confirmed,” Rose said. “Delayed initiation of treatment and longer time to normalization of thyroid function are associated with poorer intellectual outcomes.”
When newborn screening indicates congenital hypothyroidism, a physical examination should be performed and serum concentrations of TSH and free T4 measured. Elevated TSH with low free T4 is indicative of overt primary hypothyroidism. Elevated TSH with normal free T4 is termed hyperthyrotropinemia or mild hypothyroidism. Newborns with normal TSH and low free T4 typically have central hypothyroidism, prematurity, low birth weight, acute illness or T4-binding globulin deficiency.
If congenital hypothyroidism is confirmed, treatment begins with levothyroxine at a starting dose of 10 µg/kg to 15 µg/kg per day, with tablets being the typical formulation. The FDA has recently approved a liquid formulation of levothyroxine for use in children. Providers should not wait for thyroid imaging to begin treatment. Formulations prepared by compounding pharmacies should be avoided, according to the authors, due to an unreliability in dosing. TSH and free T4should be monitored every 1 to 2 months up to age 6 months, every 2 to 3 months from age 7 to 12 months, and every 3 to 4 months from age 1 to 3 years. Liothyronine is not indicated for newborns, and there is no evidence that adding liothyronine to levothyroxine will improve patient outcomes.
Congenital hypothyroidism is considered permanent if there is thyroid dysgenesis or if serum TSH increases above 10 mIU/L after the first year of life. Those who are not yet diagnosed with permanent congenital hypothyroidism can trial off of levothyroxine therapy at age 3 years under endocrinologist supervision to assess whether lifelong treatment is needed.
Children diagnosed with congenital hypothyroidism should have their behavioral and cognitive development closely monitored during infancy and early childhood because they may have a higher risk for neurocognitive and socioemotional dysfunction, even with proper treatment. Additionally, a formal hearing evaluation should be considered if there is concern for a hearing deficit or abnormal language development because children with congenital hypothyroidism have an increased risk for hearing deficits.
Guidance for ill newborns, twins
The guideline includes specific considerations for special populations. Infants who are born prematurely, with low birth weight or those who are ill at birth may have mildly elevated TSH that may resolve after a short period or may persist and require thyroid hormone therapy.
“Pediatric endocrinologists vary in how long they are willing to monitor a mild TSH elevation without stepping in to initiate thyroid hormone therapy,” Rose said. “Long-term studies of intellectual function are limited in the context of untreated mild TSH elevation. Results of short follow-up studies vary, with some showing no significant intellectual consequences, and others showing deficits.”
For newborn twins, it is possible for a congenital hypothyroidism diagnosis to be missed due to shared blood circulation with a twin who does not have congenital hypothyroidism. Repeat screening at 2 weeks can be done to confirm a possible diagnosis in twins. Children with trisomy 21 have a high risk for autoimmune thyroid dysfunction and intellectual dysfunctions, even early in life. Repeat screening for TSH elevation is especially important in this population, according to Rose.
More evidence needs to be gathered in several areas for treating congenital hypothyroidism. One of controversy involves whether levothyroxine is necessary for newborns with mild TSH elevation of 5 mIU/L to 10 mIU/L. Previously published studies have found varying results as to whether mild congenital hypothyroidism worsens cognitive development in children. No studies have demonstrated a beneficial effect of levothyroxine on mild congenital hypothyroidism, and no studies have been able to define TSH thresholds for potential adverse outcomes in mild congenital hypothyroidism.
“Results of controlled studies to evaluate consequences of untreated mild long-term TSH elevation would be valuable,” Rose said. “However, such studies might not be considered ethical. Natural history studies in countries that do not yet perform newborn screening might provide some answers.”
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