Iodine and hypothyroidism in neonates with congenital heart disease

To evaluate the influence of the intravenous injection of iodine during cardiac catheterisation, and of topical iodine antiseptics during surgical procedures, on thyroid function in full term neonates.

Twenty one full term infants with major cardiac anomalies who survived for more than a month were studied. Thyroxine and thyrotropin concentrations were measured (by radioimmunoassay) before each procedure, 24 hours after the procedure, and every week thereafter until the age of 1 month or until normal. Thyroxine values less than 64.4 nmol/l were considered low, while thyrotropin values greater than 30 mU/l were considered high.

Thyroid function tests before iodine exposure were within normal limits in all infants. Following catheterisation or surgery six infants had raised thyrotropin concentrations; three had low thyroxine concentrations. Two of those infants were treated with L-thyroxine.

Iodine exposure during cardiac catheterisation or surgery may induce transient hypothyroidism in term infants.