Hyperthyrotropinemia at 2 weeks of age indicates thyroid dysfunction and predicts the occurrence of delayed elevation of thyrotropin in very low birth weight infants

Abstract

For preterm infants, transient hypothyroxinemia of prematurity and transient primary hypothyroidism, especially with delayed elevation of serum thyrotropin (TSH), are important. To address the above two issues, we performed thyrotropin-releasing hormone (TRH) stimulation tests at about 2 weeks of age for 31 preterm infants with a gestational age of 30 weeks or less. For basal TSH levels, 68% of infants (21 of 31) showed normal values (TSH < 10 mU/l) and 32% of infants (10 of 31) showed higher values (four infants: TSH 10-15 mU/l, six infants: TSH > 15 mU/l). Peak TSH values in response to TRH stimulation tests ranged from 9·76 to 114·8 mU/l. All infants showed a significant response to TRH stimulation tests. Only 9·5% of infants (two of 21) with normal basal TSH values showed a hyperresponse (peak TSH > 45 mU/l), whereas 80% of infants (eight of 10) who had higher basal TSH values showed a hyperresponse. All infants who showed mildly elevated basal TSH values (TSH 10-15 mU/l) and a hyperresponse to TRH stimulation tests showed delayed elevation of basal TSH values (TSH > 15 mU/l) later. Thyrotropin-releasing hormone stimulation tests at about 2 weeks of age suggested that the hypothalamic-pituitary-thyroid axis might be established even in extremely premature infants. Basal increased TSH levels (TSH > 10 mU/l) and a hyperresponse to TRH stimulation tests (peak TSH > 45 mU/l) suggested subclinical thyroid dysfunction. Serum TSH values at about 2 weeks of age could be useful for the prediction of delayed TSH elevation.