Thyroglobulin as a marker of iodine nutrition status in the general population

Abstract

Objective: The iodine status of a population is traditionally evaluated by either urinary iodine (UI) excretion or by some measure of thyroid volume and the prevalence of goitre. In this prospective study of a mandatory iodization programme, we aimed to evaluate serum thyroglobulin (Tg) as a marker of iodine status in the population. Methods: Two identical cross-sectional studies were performed before (1997-1998, nZ4649) and after (2004-2005, nZ3570) the initiation of the Danish iodization programme in two areas with mild and moderate iodine deficiency. Serum Tg was measured from blood samples. Thyroid volume was measured by ultrasonography. Results: Before iodization, the median serum Tg was considerably higher in moderate than in mild iodine deficiency. Iodization led to a lower serum Tg in all examined age groups. The marked preiodization difference in Tg level between the regions was eliminated. The prevalence of Tg above the suggested reference limit (40 mg/l) decreased from 11.3 to 3.7% (P!0.0001). Using bootstrapping, we demonstrated a higher efficacy of Tg than of thyroid volume to show a difference between pre-and post-iodization values. Conclusion: We found serum Tg to be a suitable marker of iodine nutrition status in the population. The results may suggest that the Danish iodization programme has led to a sufficient iodine intake, even if the median UI excretion is still marginally low according to WHO criteria.

Thyroglobulin as a Biomarker of Iodine Deficiency: A Review

“…Of these, nine were randomized controlled trials, two were nonrandomized controlled trials, three were cohort observational studies, 23 were cross-sectional studies (10 multicenter), and one was a monitoring report of iodization programs that included a measurement before the introduction of iodized salt to a measurement after the introduction of iodized salt. In order to investigate the consistency of the relationship between iodine status as determined by UIC and Tg more clearly, for those studies that reported this information for more than one group, we considered each of these groups separately (i.e., one study of pregnant women and their newborns (37); one study of pregnant women and adults (38); one study of children and adults (30); three studies of children living in different regions (39) or countries (40,41); and seven studies of adults living in different regions (21,25,(42)(43)(44) or countries (45,46)). …”

“…Seven studies (21,25,30,38,43,45,46) showed that iodine deficient adults had a median Tg ‡13 lg/L (range 16-69 lg/L), while only one study (45) reported that iodine-sufficient adults had a median Tg ‡ 13 lg/L. However, 8 of 12 studies (21,25,(42)(43)(44)72,90,91) reported that adults who were categorized as iodine deficient had a median Tg <13 lg/L. One of these studies (42) included adults with iodine excess (i.e., median UIC ‡300 lg/L) who, in contrast to the findings of Zimmermann et al (41) in schoolchildren, had a median Tg <13 lg/L.…”

“…In addition to increasing the synthesis and proteolysis of Tg, TSH also stimulates the growth and division of the follicular cells, which causes the thyroid gland to enlarge (i.e., goiter) (19). In iodine deficiency, an increased amount of Tg is released into the blood (20), which is positively correlated with thyroid volume (21). For example, healthy adults have a mean Tg concentration ranging from 5 to 14 lg/L (22)(23)(24)(25)(26)(27).…”

Serum thyroglobulin before and after iodization of salt: an 11-year DanThyr follow-up study

“…Therefore, it has been suggested that serum Tg values in a population is a sensitive marker of iodine intake, and that serum Tg can be used to monitor the iodine status of a population. However, only few studies have investigated serum Tg in relation to iodine fortification (IF) (18,19,20,21), and no previous longitudinal study gave information on serum Tg both before and after IF.…”

Development, characterization and clinical validation of new sensitive immunofluorometric assay for the measurement of serum thyroglobulin

“…This pathway is now recognized as a control mechanism of thyroid hormone release (3). Binding of Tg to megalin depends on conformation, and the degree of iodination, which has conformational consequences, is one of the mechanisms that alter serum Tg levels independently of TSH stimulation (4).…”