Urinary iodine concentration is currently the most practical biochemical
marker for iodine nutrition when carried out with appropriate technology
and sampling. This approach assesses iodine nutrition only at the
time of measurement, whereas thyroid size reflects iodine nutrition over
months or years. Therefore, even though populations may have attained
iodine sufficiency on the basis of median urinary iodine concentration,
goitre may persist, even in children.