Context: Thyroglobulin (Tg) may be a valuable indicator of improving thyroid function in children after salt iodization. A recently-developed Tg assay for use on dried whole blood spots (DBS) makes sampling practical even in remote areas.

Objective: The study aim was to develop a reference standard for DBS-Tg, establish an international reference range for DBS-Tg in iodine-sufficient children, and test the standardized DBS-Tg assay in an intervention trial.

Design, participants, and interventions: Serum Tg reference material of the European Community Bureau of Reference (CRM-457) was adapted for DBS and its stability tested over one year. DBS-Tg was determined in an international sample of 5-14 y-old children (n = 700), who were euthyroid, antiTg antibody-negative, and residing in areas of long-term iodine sufficiency. In a 10-month trial in iodine-deficient children, DBS-Tg and other indicators of iodine status were measured before and after introduction of iodized salt.

Results: Stability of the CRM-457 Tg reference standard on DBS over 1 y of storage at -20° and -50°C was acceptable. In the international sample of children, the 3^rd and 97^th percentiles of DBS-Tg were 4 µg/L and 40 µg/L, respectively. In the intervention, before introduction of iodized salt, median DBS-Tg was 49 µg/L and over 2/3rds of children had DBS-Tg values >40 µg/L. After 5 and 10 mo of iodized salt use, median DBS-Tg decreased to 13 and 8 µg/L, and only 7% and 3% of children had values >40 µg/L. DBS-Tg correlated well at baseline and 5 months with urinary iodine and thyroid volume.

Conclusions: The availability of reference material and an international reference range facilitates the use of DBS-Tg for monitoring of iodine nutrition in school-age children.