Original Article

Basal serum thyroxine level should guide initial thyroxine replacement dose in neonates with congenital hypothyroidism


  • Ceren Günbey
  • Alev Özön
  • E. Nazlı Gönç
  • Ayfer Alikaşifoğlu
  • Sevilay Karahan
  • Nurgün Kandemir

Received Date: 15.08.2020 Accepted Date: 17.12.2020 J Clin Res Pediatr Endocrinol 0;0(0):0-0 [e-Pub] PMID: 33374096


Initial high-dose Na-L thyroxine (Na-LT4) (10-15 μg/kg/day) replacement for primary congenital hypothyroidism (CH) is recommended in guidelines. However, high-dose Na-LT4 has risks. In this study, we aimed to investigate normalizing effect of varying initial doses of Na-LT4 on serum thyroid hormone levels.


Fifty-two patients were analyzed retrospectively. The patients were classified into mild (27/51.9%), moderate (11/21.1%) and severe (14/26.9%) CH with respect to initial free thyroxine (FT4) levels. Time taken to achieve target hormone levels was compared within groups.


Initial mean Na-LT4 doses for mild, moderate and severe disease were 6.9±3.3, 9.4±2.2 and 10.2±2 μg/kg/day. Serum FT4 levels reached the upper half of normal range (>1.32 ng/dL) in a median of 16, 13 and 16 days in patients with mild, moderate and severe CH with the mean time from initial treatment to first control visit 14.8 ± 6 days (range 1-36). There was no significant difference in terms of time to achieve target FT4 hormone levels according to disease severity (p=0.478). Seven (25.9%), 8 (72.7%) and 8 (57.1%) patients experienced hyperthyroidism (serum FT4 >1.94 ng/dL) in mild, moderate, severe CH groups in the first visit, respectively (p=0.016).


Not all patients diagnosed with CH require high-dose Na-LT4, initial dose of Na-LT4 may be tailored based on pre-treatment thyroid hormone levels. Some patients with moderate and severe CH, experienced iatrogenic hyperthyroidism even though the dose was close to the lower limit of the recommended range in guidelines; suggesting lower initial doses and closer follow-up within the first week.

Keywords: Newborn screening, children, congenital hypothyroidism, Na-L thyroxine, dose