Assessment of iodine status using dried blood spot thyroglobulin: development of reference material and establishment of an international reference range in iodine-sufficient children.
BACKGROUND
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.


METHODS
Serum Tg reference material of the European Community Bureau of Reference (CRM-457) was adapted for DBS and its stability tested over 1 yr. DBS-Tg was determined in an international sample of 5- to 14-yr-old children (n = 700) who were euthyroid, anti-Tg 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 yr of storage at -20 and -50 C was acceptable. In the international sample of children, the third and 97th percentiles of DBS-Tg were 4 and 40 microg/liter, respectively. In the intervention, before introduction of iodized salt, median DBS-Tg was 49 microg/liter, and more than two thirds of children had DBS-Tg values greater than 40 microg/liter. After 5 and 10 months of iodized salt use, median DBS-Tg decreased to 13 and 8 microg/liter, respectively, and only 7 and 3% of children, respectively, had values greater than 40 microg/liter. 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.
Zimmermann
Michael B
MB
Laboratory for Human Nutrition, Swiss Federal Institute of Technology, LFV E19, Schmelzbergstrasse 7, CH-8092 Zürich, Switzerland. michael.zimmermann@ilw.agrl.ethz.ch
de Benoist
Bruno
B
Corigliano
Sandro
S
Jooste
Pieter L
PL
Molinari
Luciano
L
Moosa
Khairya
K
Pretell
Eduardo A
EA
Al-Dallal
Zuhair Salman
ZS
Wei
Yao
Y
Zu-Pei
Chen
C
Torresani
Toni
T
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003677:Deficiency Diseases / Q000178:diet therapy; D005062:European Union / Q000458:organization & administration; D005260:Female; D006801:Humans; D007455:Iodine / Q000097:blood* / Q000172:deficiency / Q000627:therapeutic use / Q000652:urine; D008297:Male; D012015:Reference Standards; D012016:Reference Values; D017673:Sodium Chloride, Dietary / Q000627:therapeutic use; D013954:Thyroglobulin / Q000032:analysis*; D013959:Thyroid Diseases / Q000178:diet therapy; D013960:Thyroid Function Tests / Q000379:methods / Q000592:standards*; D014944:World Health Organization / Q000458:organization & administration
D017673:Sodium Chloride, Dietary; C034024:iodized salt; D013954:Thyroglobulin; D007455:Iodine