Serum thyroglobulin and urinary iodine concentration are the most appropriate indicators of iodine status and thyroid function under conditions of increasing iodine supply in schoolchildren in Benin

Iodine deficiency control programs have greatly reduced iodine deficiency d isorders worldwide. For monitoring changes in iodine status, different indi cators may be used. The aim of this study was to evaluate the suitability o f indicators of iodine status and thyroid function, thyroglobulin (Tg), thy roid-stimulating hormone (TSH) and free thyroxine (FT4) in serum, thyroid v olume and urinary iodine concentration, in iodine-deficient schoolchildren under conditions of increasing iodine supply. The study was established as a double-blind, placebo-controlled oral administration of a single dose of iodized oil to schoolchildren (7-10 y old), living in an iodine-deficient a rea of Benin, with an observation period of 10 mo. However, 3-4 mo after su pplementation, iodized salt became available In the area. The study populat ion therefore comprised an iodized oil-supplemented group and a nonsuppleme nted group, both of which had variable, uncontrolled intakes of iodized sal t during the last 6 mo of the study. Initial mean serum concentrations of T SH and FT4 were within the normal range, whereas serum Tg concentration, ur inary iodine concentration and thyroid volume were indicative of mode rate- to-severe iodine deficiency. At the end of the study, all indicators had im proved significantly, except thyroid volume, which had decreased only in th e supplemented group. The supplemented group also still had significantly l ower serum Tg and higher urinary Iodine concentrations than the nonsuppleme nted group. Serum Tg and urinary iodine concentrations are the indicators m ost Influenced by a changing iodine supply. Current normal reference ranges of serum concentrations of TSH and FT4 are too wide for detecting iodine d eficiency in this age group.