ESPE Abstracts

Background: Neonatal hyperthyrotropinaemia (HT) is defined by elevated thyroid stimulating hormone (TSH) and normal free-thyroxine (FT4) level. Persistent HT in the neonatal period is often a diagnostic dilemma for clinicians to either treat to prevent subclinical hypothyroidism or to wait and monitor thyroid function tests (TFTs).

Methods: As part of an audit, 1,449 term infants who had TFTs undertaken as part of a prolonged jaundice screen from 2012-2017 were reviewed. Infants with HT (defined by TSH>5mU/L) were followed up in clinic. We evaluated perinatal factors and TFTs were monitored in 2-4 weeks, then regularly 2-4 monthly until 2 years of age or until HT resolved.

Results: There were 37 term infants (27 males) with a raised TSH (>5mU/L) and normal FT4 level over the 5-year period. This represents 2.6% of the 1,449 term infants found to have HT. All infants with HT were born in good condition. Mean gestation was 38.1 weeks (±2.1 SD, range 33.1-42.0). 4 infants had Trisomy 21 and 3 infants had a maternal history of hypothyroidism. In 2 infants, we started levothyroxine treatment due to rising TSH and falling FT4 levels. 9% of infants had TSH normalised to 5mU/L in 4 weeks without treatment, 54% normalised their TSH in 8 weeks, 83% normalised in 3-6 months, 94% normalised in 12 months and 1 patient had persistent TSH >5mU/L which did not require treatment at 24 months.

Conclusions: In 95% of all the cases of HT in well term infants, the natural course was that the TSH resolved to normal < 5mU/L by 2 years of age. In 3% of cases, TSH remained elevated (> 5mU/L) at 2 years but FT4 levels were normal and in the upper quartile range (>15pmol/L) without treatment. We recommend TFTs monitoring due to the risk of decompensation although the risk of decompensation is low; and frequency of monitoring can be reduced after 2 years.