Suppression of TSH in congenital hypothyroidism is significantly related to serum levels and dosage of thyroxine

Aim: To assess thyrotropin (thyroid-stimulating hormone; TSH) suppression and serum thyroxine (T-4) concentrations in infants with congenital hypothyroidism in relation to T-4 dose and pretreatment parameters. Method. A retrospective study of all cases treated in a single centre since neonatal screening began was performed. Results: In 54 infants treated with a mean daily T-4 dose of 9.8 mug/kg, the TSH concentration was suppressed (<6 mU/I) in 65% of the cases by 6 months with the serum T-4 level at the upper end of the infant reference range. Infants who suppressed their TSH later did not differ in pretreatment serum TSH or T-4 concentration. T-4 dose and serum T-4 level were lower in infants whose TSH was not suppressed. Conclusions: TSH suppression in congenital hypothyroidism is significantly related to serum levels and dosage of T-4. We suggest that a delay in TSH suppression is mainly due to undertreatment. Copyright (C) 2003 S. Karger AG, Basel.