Euthyroid Collaboration

I2XS Iodine Excess

Does exposure to iodine cause transient hypothyroidism?

Click Here for an overview of iodine excess and thyroid function

Background Exposure to iodinated contrast media might cause transient hypothyroidism in extreme preterm infants. As the brain is thyroid hormone dependent for at least the first two years, such exposure might be associated with poor neurodevelopment. The rationale for using iodinated contrast media is to visualise the placement of central venous catheters whereby minimizing the threat of a serious adverse outcome resulting from a wrongly positioned catheter.

Use of contrast media has been associated with a reduction in serious complication from 1.8% to 0.05%. The literature about the adverse consequences of using iodinated contrast media is limited. As a consequence there is variation in the use of contrast media in neonatal intensive care units across the UK. Our proposal is to use this variance in management to determine the impact on thyroid function.

Key Points

  • Thyroxine is critical for the developing human brain and this supply is compromised whether serum T4 levels are reduced through transient hypothyroxinaemia, which has a contribution from iodine deficiency, or from transient hypothyroidism caused by iodine excess.
  • Maternal exposure to iodine (e.g. povidone-iodine use for skin disinfectant during Caesarean section or vaginal delivery) results in neonatal iodine overload.
  • Breast feeding and neonatal iodine exposure (e.g. via the mother, for umbilical cord care or for skin disinfectant) results in maximal neonatal iodine overload.
  • The impact of iodine overload in infants when iodine deficiency is endemic is greater than to those born into iodine sufficient environments.
  • Preterm infants are more vulnerable to the effects of iodine exposure compared to term infants.
  • British National Formulary for Children 2005 lists neonates under 32 weeks and infants under 1.5kg as contra-indications

Main research question: What is the incidence of transient hypothyroidism following exposure to iodine in infants less than 32 weeks gestation?

Project status: pilot work is ongoing in collaboration with 7 neonatal units in the UK

Funding: Tenovus (Scotland), Anonymous Trust