BACKGROUND
Neonatal screening for hypothyroidism is universal in the United States because starting levothyroxine as soon as possible in babies diagnosed with hypothyroidism is extremely important in making sure the brain develops normally. In contrast, hyperthyroidism in newborns is seen in 1:5600 live births, although severe cases requiring treatment is much less common and is seen in 1:12,174 live births. The most common cause of neonatal hyperthyroidism is a due to thyroid stimulating antibodies in the mother with a history of Graves’ disease crossing over the placenta to affect the baby’s thyroid. In mothers with thyroid stimulating antibodies, the chances of her passing on to her baby is 1% to 5%. Since the risk is low, relying only on the history of the mother having Graves’ disease might not be enough to detect those babies that are at risk of developing hyperthyroidism. Also, relying on the history and blood measurements of antibodies in the mother would not help to identify babies with rare genetic causes of hyperthyroidism. Sadly, around 25% of neonatal hyperthyroidism leads to increased early death from congestive heart failure and premature birth. Therefore, it is important to diagnose and treat early by using a screening test.

This study examines samples from the neonatal TSH screening program in France to determine a threshold to identify patients with neonatal hyperthyroidism.

THE FULL ARTICLE TITLE
Banigé M et al 2022 Neonatal screening for hyperthyroidism proof of concept. J Clin Endocrinol Metab 107(4):e1374–e1381. PMID: 34894265.

SUMMARY OF THE STUDY
Past data in France from 48 cases of neonatal hyperthyroidism (31 moderate and 17 severe) and 24,862 controls (newborns with TSH born on the same days as the newborns with hyperthyroidism) was collected. Neonatal hyperthyroidism was defined based on clinical suggestion, such as elevated heart rate, heart failure, very excitable, and poor weight gain, but the presence of enlarged thyroid was not necessary. Moderate neonatal hyperthyroidism was described as neonatal hyperthyroidism requiring long stay in hospital but not needing anti-thyroid drugs (ATD) treatment. Severe neonatal hyperthyroidism was described as neonatal hyperthyroidism requiring admission to the neonatal ICU and ATD treatment. TSH levels were analyzed on day 3 after birth, and cases of neonatal hyperthyroidism were separated in three groups (all cases, moderate, and severe) and compared with control cases.

Results showed that, while the average TSH level (0.57 mIU/L) for all neonatal hyperthyroidism cases was lower than control cases, it was not enough to clearly separate babies with hyperthyroidism with babies that were normal. However, using a screening TSH level of <0.18 mIU/L detected 25% of neonatal hyperthyroidism cases and all of the cases with a genetic cause. This limit showed potential for detection of severe neonatal hyperthyroidism.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The authors determined a screening TSH level <0.18 mIU/L checked on day 3 post-delivery is ideal to diagnose severe neonatal hyperthyroidism. Combining this threshold, along with a history of the mother having Graves’ disease, the vast majority of babies with neonatal hyperthyroidism can be identified.

— Joanna Miragaya, MD and Ebru Sulanc, MD

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