Neonatal TSH screening: is it a sensitive and reliable tool for monitoring iodine status in populations?

Iodine deficiency is the most common cause of preventable brain damage in the newborn. The indicators for assessing iodine nutritional status include urinary iodine excretion, thyroid size, thyroid stimulating hormone (TSH) and thyroglobulin (Tg) concentrations in the blood. Neonatal TSH concentration is increased when the supply of thyroid hormone and iodine from the maternal circulation to the foetus has been compromised. The World Health Organization (WHO) has suggested that when a sensitive assay is used on samples collected 3-4 days after birth, a <3% frequency of TSH concentrations >5 mIUl(-1) indicates iodine sufficiency in a population. However, many studies have attempted to apply the frequency of neonatal TSH values >5 mIUl(-1) in determining population iodine status and monitoring intervention programmes, and although some have proven to be successful, most have provided conflicting or uncertain data. This is due to the many technical issues that remain unresolved on the use of neonatal TSH screening for monitoring iodine status, making it doubtful as a sensitive and reliable quantitative tool. More research is required to resolve these issues. In the interim, WHO should consider withdrawing its current guidelines for neonatal TSH screening for monitoring iodine deficiency in populations.