Serum Tg--a sensitive marker of thyroid abnormalities and iodine deficiency in epidemiological studies

Exploration of thyroglobulin as a biomarker of iodine status in iodine-sufficient and mildly iodine-deficient pregnant women

PURPOSE

Urinary iodine-to-creatinine ratio (UI/Creat) reflects recent iodine intake but has limitations for assessing habitual intake. Thyroglobulin (Tg) concentration, which increases with thyroid size, appears to be an indicator of longer-term iodine status in children and adults, however, less is known in pregnancy. This study investigated the determinants of serum-Tg in pregnancy and its use as an iodine-status biomarker in settings of iodine-sufficiency and mild-to-moderate deficiency.

METHODS

Stored blood samples and existing data from pregnant women from the Netherlands-based Generation R (iodine-sufficient) and the Spain-based INMA (mildly-to-moderately iodine-deficient) cohorts were used. Serum-Tg and iodine status (as spot-urine UI/Creat) were measured at median 13 gestational weeks. Using regression models, maternal socio-demographics, diet and iodine-supplement use were investigated as determinants of serum-Tg, as well as the association between UI/Creat and serum-Tg.

RESULTS

Median serum-Tg was 11.1 ng/ml in Generation R (n = 3548) and 11.5 ng/ml in INMA (n = 1168). When using 150 µg/g threshold for iodine deficiency, serum-Tg was higher in women with UI/Creat < 150 vs ≥ 150 µg/g (Generation R, 12.0 vs 10.4 ng/ml, P = 0.010; INMA, 12.8 vs 10.4 ng/ml, P < 0.001); after confounder adjustment, serum-Tg was still higher when UI/Creat < 150 µg/g (regression coefficients: Generation R, B = 0.111, P = 0.050; INMA, B = 0.157, P = 0.010). Iodine-supplement use and milk intake were negatively associated with serum-Tg, whereas smoking was positively associated.

CONCLUSION

The association between iodine status and serum-Tg was stronger in the iodine-deficient cohort, than in the iodine-sufficient cohort. Serum-Tg might be a complementary (to UI/Creat) biomarker of iodine status in pregnancy but further evidence is needed.

Thyroid autoimmunity in Greenlandic Inuit

Objective

This study aimed to provide the first data on the occurrence of thyroid autoimmunity among Inuit in Greenland, a distinct ethnic group who is not iodine deficient.

Design

This study is a population-based cross-sectional study.

Methods

Data were collected in Nuuk in West Greenland and in Ammassalik district in East Greenland. Information on lifestyle, diet and diseases was obtained using questionnaires. Thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb) and thyroid-stimulating hormone (TSH) were measured in serum. Iodine and creatinine were measured in spot urine samples.

Results

The participation rate was 95% with 434 Inuit participants; 75% were smokers. Iodine excretion was 169 µg/24 h in urban West Greenland, 224 µg/24 h in the main town and 228 µg/24 h in settlements in rural East Greenland. TPOAb, TgAb or either of these was measured in the serum from 3.7, 5.9 and 8.3% of participants, respectively. TPOAb or TgAb was found in 9.3% of Inuit women and 7.5% of men and more frequently, in East Greenland Inuit with the higher iodine excretion (P = 0.02). There was some evidence suggesting that thyroid autoimmunity was more frequent among non-smokers (12.5%) compared to smokers (7.0%). Harbouring a thyroid autoantibody was most frequent in participants with TSH above 3.6 mIU/L (P < 0.001).

Conclusion

Thyroid autoantibodies were rare among Greenland Inuit. While iodine nutrition was associated with autoimmunity similarly to other ethnic groups, the influence of sex and smoking was limited. This could suggest genetic component in Inuit, but the impact of cold, selenium and persistent organic pollutants needs to be elucidated.

Thyroglobulin levels among iodine deficient pregnant women living in Northern Ireland

BACKGROUND

Iodine deficiency has re-emerged among pregnant cohorts in the UK. Thyroglobulin (Tg) is a protein produced uniquely by the thyroid gland which appears to mount a U-shaped response to extremes of iodine status. Tg has been suggested as an alternative marker for chronic iodine deficiency but the value of Tg in pregnancy has not been fully elucidated. A recent non-European study suggested a median Tg ≤10 µg/L with <3% of values >44 µg/L was indicative of sufficiency in the second trimester of pregnancy.

METHODS

We measured serum Tg levels in each trimester in 241 pregnant women living in Northern Ireland, a population with mild iodine deficiency at all stages of pregnancy as defined by urinary iodine concentration (UIC) and iodine: creatinine ratio (ICR). Women with Tg antibodies (6% in 1st trimester) were excluded.

RESULTS

The median UIC in this cohort was in the deficient range at 73, 94 and 117 µg/L in sequential trimesters (adequacy ≥ 150 µg/L). Corresponding median Tg levels were 19, 16 and 16 µg/L respectively. Median Tg for all samples was 17 μg/L (IQR 11-31) suggestive of iodine deficiency. Tg was >44 μg/L in 14.3%, 9.4% and 12.4% of women in sequential trimesters respectively. Women with either UIC/ICR below the cut-offs 150 µg/L and 150 µg/g creatinine had higher Tg concentrations in 1st and 2nd trimester (p < 0.01; p < 0.001) but not in 3rd trimester.

CONCLUSION

This study adds to the evolving evidence that Tg measurement is of value in reflecting iodine status in pregnancy.

TSH Mediated the Effect of Iodized Salt on Child Cognition in a Randomized Clinical Trial

Objectives:

This study examines the hormonal mediators of the effect of iodized salt in pregnancy on child cognition.

Methods:

Sixty districts across 6 zones in the Amhara region of Ethiopia were randomly allocated to a control or intervention arm of early market access to iodized salt. Twenty-two villages per arm were randomly selected for this sub-study. A total of 1220 pregnant women who conceived after the intervention began were enrolled and assessed for their iodine and iron status. Data were collected once on the household socio-demographic status and iodized salt use, and maternal urinary iodine during pregnancy. Then, infants’ diet, urinary iodine level, cognitive development (Bayley III), serum hormonal levels, iron status, and inflammation markers were measured between 2 and 13 months of age.

Results:

The median maternal urinary iodine concentration was adequate and significantly higher in the intervention mothers than that of the controls (163 vs 121 µg/L, P < .0001). Intervention children compared to the control children had lower thyroid-stimulating hormone (TSH) (mean: 2.4 ± 1.0 µIU/mL vs 2.7 ± 1.0 µIU/mL, effect size = 0.18, P < .01) and thyroglobulin (Tg) (41.6 ± 1.0 ng/mL vs 45.1 ± 1.0 ng/mL, effect size = 0.14, P < .05). There was an interaction between the intervention and iron stores such that cognition was higher with iron (effect size = 0.28, 100 vs 94 IQ points). TSH was a partial mediator (12%) of the effect of the intervention on child cognition (Sobel z-score = 2.1 ± 0.06, P < .05).

Conclusion:

TSH partially mediated the effect of the iodized salt intervention on child cognition.

Variability of Thyroid Measurements from Ultrasound and Laboratory in a Repeated Measurements Study

BACKGROUND

Variability of measurements in medical research can be due to different sources. Quantification of measurement errors facilitates probabilistic sensitivity analyses in future research to minimize potential bias in epidemiological studies. We aimed to investigate the variation of thyroid-related outcomes derived from ultrasound (US) and laboratory analyses in a repeated measurements study.

SUBJECTS AND METHODS

Twenty-five volunteers (13 females, 12 males) aged 22-70 years were examined once a month over 1 year. US measurements included thyroid volume, goiter, and thyroid nodules. Laboratory measurements included urinary iodine concentrations and serum levels of thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), and thyroglobulin. Variations in continuous thyroid markers were assessed as coefficient of variation (CV) defined as mean of the individual CVs with bootstrapped confidence intervals and as intraclass correlation coefficients (ICCs). Variations in dichotomous thyroid markers were assessed by Cohen's kappa.

RESULTS

CV was highest for urinary iodine concentrations (56.9%), followed by TSH (27.2%), thyroglobulin (18.2%), thyroid volume (10.5%), fT3 (8.1%), and fT4 (6.3%). The ICC was lowest for urinary iodine concentrations (0.42), followed by fT3 (0.55), TSH (0.64), fT4 (0.72), thyroid volume (0.87), and thyroglobulin (0.90). Cohen's kappa values for the presence of goiter or thyroid nodules were 0.64 and 0.70, respectively.

CONCLUSION

Our study provides measures of variation for thyroid outcomes, which can be used for probabilistic sensitivity analyses of epidemiological data. The low intraindividual variation of serum thyroglobulin in comparison to urinary iodine concentrations emphasizes the potential of thyroglobulin as marker for the iodine status of populations.

Inadequate iodine intake in lactating women in Sweden: A pilot 1-year, prospective, observational study

INTRODUCTION

Breastfed infants depend on breast-milk iodine for growth and brain development, as iodine is a trace element important for thyroid hormone production. Iodine need is higher during lactation; hence, mothers and children are at risk of iodine deficiency. We aimed to explore maternal iodine and thyroidal status during lactation.

MATERIAL AND METHODS

Pregnant women were recruited in Gothenburg, southwest Sweden. Maternal urine and serum were collected at pregnancy week 35-37 (n = 84) and 0.5, 4, and 12 months postpartum. Seventy mothers provided breast milk at 0.5 months.

RESULTS

Median (interquartile range) breast-milk iodine concentration was 90 (66-116) μg/L. About 58% had breast-milk iodine concentration <100 μg/L. Iodine supplement users (n = 13) had higher breast-milk iodine concentration than non-users (n = 49) (140 μg/L vs 71 μg/L, P = .001). Exclusively breastfeeding women at 4 months postpartum (n = 57) had lower median urinary iodine concentration (85 μg/L vs 133 μg/L, P = .004) and higher thyroglobulin serum concentration (22.3 μg/L vs 11.8 μg/L, P = .032) than non-exclusively breastfeeding women (n = 25). Concentrations of thyroid hormones were unaffected.

CONCLUSIONS

This pilot study suggests that lactating women in southwest Sweden present mildly inadequate iodine intake, mainly among non-iodine supplement users and exclusively breastfeeding mothers. Studies on the coverage of the iodine fortification program in breastfeeding women are warranted.

Iodine, Thyroglobulin and Thyroid Gland

Iodine is essential in the biosynthesis of thyroid hormones that affect metabolic processes in the organism from the prenatal state to the elderly. The immediate indicator of iodine intake is the concentration of iodine in urine, but the indicator of iodine intake in the longer term of several months is thyroglobulin (Tg). Tg negatively correlated with increasing intake of iodine in population that do not suffer from thyroid disease, while a more than adequate to excessive iodine intake leads to an increase in Tg. The dependence of Tg on iodine can be described by a U-shaped curve. Thyroglobulin in serum is elevated in thyroid disease mainly in hyperthyroidism (diagnosis E05 of WHO ICD-10 codes) and in goiter (diagnosis E04 of WHO ICD-10 codes). Tg values decrease below 20 µg/l after effective treatment of patients with thyroid disease. Thyroglobulin may thus be an indicator of thyroid stabilization and the success of the thyroid gland treatment.

The Joint Role of Thyroid Function and Iodine Status on Risk of Preterm Birth and Small for Gestational Age: A Population-Based Nested Case-Control Study of Finnish Women

Normal maternal thyroid function during pregnancy is essential for fetal development and depends upon an adequate supply of iodine. Little is known about how iodine status is associated with preterm birth and small for gestational age (SGA) in mildly iodine insufficient populations. Our objective was to evaluate associations of early pregnancy serum iodine, thyroglobulin (Tg), and thyroid-stimulating hormone (TSH) with odds of preterm birth and SGA in a prospective, population-based, nested case-control study from all births in Finland (2012–2013). Cases of preterm birth (n = 208) and SGA (n = 209) were randomly chosen from among all singleton births. Controls were randomly chosen from among singleton births that were not preterm (n = 242) or SGA (n = 241) infants during the same time period. Women provided blood samples at 10–14 weeks’ gestation for serum iodide, Tg and TSH measurement. We used logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for preterm birth and SGA. Each log-unit increase in serum iodide was associated with higher odds of preterm birth (adjusted OR = 1.19, 95% CI = 1.02–1.40), but was not associated with SGA (adjusted OR = 1.01, 95% CI = 0.86–1.18). Tg was not associated with preterm birth (OR per 1 log-unit increase = 0.87, 95% CI = 0.73–1.05), but was inversely associated with SGA (OR per log-unit increase = 0.78, 95% CI = 0.65–0.94). Neither high nor low TSH (versus normal) were associated with either outcome. These findings suggest that among Finnish women, iodine status is not related to SGA, but higher serum iodide may be positively associated with preterm birth.

Iodine Deficiency, Still a Global Problem?

Iodine Deficiency Disorders are a major public health problem worldwide affecting all groups of people of which children and lactating women are the most vulnerable categories. At a global scale, aproximately 2 billion people suffer of iodine deficiency (ID) of which aproximately 50 million present with clinical manifestations. Assesing iodine levels through different methods has proven to have a key role when discussing treatment options. Screening programs, and early ID diagnostic is important for pregnant women’s follow-up, especially in known countries with iodine dificiency. Universal salt iodization programs have been proposed over the world, but unfortunately have covered about 71% of the world’s population. The aim of this article is to adress the current standings of iodine status and influence on general population with a general focus on newborns and pregnant women and to review the worldwide perspective on available prevention methods.

Thyroglobulin level at week 16 of pregnancy is superior to urinary iodine concentration in revealing preconceptual and first trimester iodine supply

Pregnant women are prone to iodine deficiency due to the increased need for iodine during gestation. Progress has recently occurred in establishing serum thyroglobulin (Tg) as an iodine status biomarker, but there is no accepted reference range for iodine sufficiency during pregnancy. An observational study was conducted in 164 pregnant women. At week 16 of gestation urinary iodine concentration (UIC), serum Tg, and thyroid functions were measured, and information on the type of iodine supplementation and smoking were recorded. The parameters of those who started iodine supplementation (≥150 μg/day) at least 4 weeks before pregnancy (n = 27), who started at the detection of pregnancy (n = 51), and who had no iodine supplementation (n = 74) were compared. Sufficient iodine supply was found in the studied population based on median UIC (162 μg/L). Iodine supplementation ≥150 μg/day resulted in higher median UIC regardless of its duration (nonusers: 130 μg/L vs. prepregnancy iodine starters: 240 μg/L, and pregnancy iodine starters: 205 μg/L, p < .001, and p = .023, respectively). Median Tg value of pregnancy starters was identical to that of nonusers (14.5 vs. 14.6 μg/L), whereas prepregnancy starters had lower median Tg (9.1 μg/L, p = .018). Serum Tg concentration at week 16 of pregnancy showed negative relationship (p = .010) with duration of iodine supplementation and positive relationship (p = .008) with smoking, a known interfering factor of iodine metabolism, by multiple regression analysis. Serum Tg at week 16 of pregnancy may be a promising biomarker of preconceptual and first trimester maternal iodine status, the critical early phase of foetal brain development.

Thyroglobulin as a Functional Biomarker of Iodine Status in a Cohort Study of Pregnant Women in the United Kingdom

BACKGROUND

Though iodine deficiency in pregnancy is a matter of public-health concern, a functional measure of iodine status is lacking. The thyroid-specific protein thyroglobulin (Tg), which reflects thyroid size, has shown promise as a functional measure in studies of children and adults, but data in pregnancy are sparse. In a cohort of mildly to moderately iodine-deficient pregnant women, this study aimed to explore whether serum Tg is a sensitive functional biomarker of iodine status and to examine longitudinal change in Tg with gestational age.

METHOD

A total of 230 pregnant women were recruited at an antenatal clinic at 12 weeks of gestation to the Selenium in PRegnancy INTervention study, in Oxford, United Kingdom. Repeated measures of urinary iodine-to-creatinine ratio, serum thyrotropin (TSH), and Tg at 12, 20, and 35 weeks of gestation were made. Women were dichotomized by their iodine-to-creatinine ratio (<150 or ≥150 μg/g) to group them broadly as iodine deficient or iodine sufficient. Women with thyroid antibodies were excluded; data and samples were available for 191 women.

RESULTS

Median Tg concentrations were 21, 19, and 23 μg/L in the first, second, and third trimesters, respectively. In a linear mixed model, controlling for confounders, Tg was higher in the <150 μg/g group than it was in the ≥150 μg/g group (p < 0.001) but there was no difference in TSH (p = 0.27). Gestational week modified the effect of iodine status on TSH (p = 0.01) and Tg (p = 0.012); Tg did not increase with gestational week in the ≥150 μg/g group, but it did in the <150 μg/g group, and TSH increased more steeply in the <150 μg/g group.

CONCLUSIONS

Low iodine status (<150 μg/g) in pregnancy is associated with higher serum Tg, suggesting that the thyroid is hyperstimulated by iodine deficiency, which causes it to enlarge. Tg is a more sensitive biomarker of iodine status in pregnancy than is TSH.

Use of thyroglobulin as a tumour marker

It is worthwhile to measure serum thyroglobulin (TG) level in thyroid cancer before subjecting patients to surgery for two reasons. Firstly, if the level is high, it may give a clue to the local and metastatic tumour burden at presentation; secondly, if the level is normal, it identifies the patients who are unlikely to show rising TG levels in the presence of thyroid cancer. Those who have high serum TG before surgery will show up recurrence as rising serum TG during the postoperative period. Those who do not have high serum TG before surgery will not show up rising serum TG in the presence of recurrent disease. In the latter situation, normal TG level gives only a false reassurance regarding recurrence of disease. Nevertheless, rising serum TG during the postoperative period must be interpreted cautiously because this could be due to the enlargement of non-cancerous residual thyroid tissue inadvertently left behind during surgery.

Breast-Milk Iodine Concentrations, Iodine Status, and Thyroid Function of Breastfed Infants Aged 2-4 Months and Their Mothers Residing in a South African Township

OBJECTIVE

Lactating women and their infants are susceptible to iodine deficiency and iodine excess. In South Africa, no data exist on the iodine status and thyroid function of these vulnerable groups.

METHODS

In a cross-sectional study, urinary iodine concentrations (UIC), thyroid function, and breast-milk iodine concentrations (BMIC) were assessed in 100 lactating women from a South African township and their 2-4-month-old breastfed infants. Potential predictors of UIC, thyroid function, and BMIC, including household salt iodine concentrations (SIC) and maternal sodium excretion, were also investigated.

RESULTS

The median (25th-75th percentile) UIC was 373 (202-627) μg/L in infants and 118 (67-179) μg/L in mothers. Median household SIC was 44 (27-63) ppm. Household SIC and maternal urinary sodium excretion predicted UIC of lactating mothers. Median BMIC was 179 (126-269) μg/L. Age of infants, SIC, and maternal UIC predicted BMIC. In turn, infant age and BMIC predicted UIC of infants. Forty-two percent of SIC values were within the South African recommended salt iodine fortification level at production of 35-65 ppm, whilst 21% of SIC were >65 ppm. Thyroid-stimulating hormone, total thyroxine, and thyroglobulin concentrations in the dried whole blood spot specimens from the infants were 1.3 (0.8-1.9) mU/L, 128±33 mmol/L, and 77.1 (56.3-105.7) μg/L, respectively, and did not correlate with infant UIC or BMIC.

CONCLUSION

Our results suggest that the salt fortification program in South Africa provides adequate iodine to lactating women and indirectly to their infants via breast milk. However, monitoring of salt iodine content of the mandatory salt iodization program in South Africa is important to avoid over-iodization of salt.

Serum thyroglobulin reference intervals in regions with adequate and more than adequate iodine intake

The purpose of this study was to establish normal thyroglobulin (Tg) reference intervals (RIs) in regions with adequate and more than adequate iodine intake according to the National Academy of Clinical Biochemistry (NACB) guidelines and to investigate the relationships between Tg and other factors.A total of 1317 thyroid disease-free adult subjects (578 men, 739 nonpregnant women) from 2 cities (Guangzhou and Nanjing) were enrolled in this retrospective, observational study. Each subject completed a questionnaire and underwent physical and ultrasonic examination. Serum Tg, thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb), Tg antibody (TgAb), and urinary iodine concentration (UIC) were measured. Reference groups were established on the basis of TSH levels: 0.5 to 2.0 and 0.27 to 4.2 mIU/L.The Tg RIs for Guangzhou and Nanjing were 1.6 to 30.0 and 1.9 to 25.8 ng/mL, respectively. No significant differences in Tg were found between genders or among different reference groups. Stepwise linear regression analyses showed that TgAb, thyroid volume, goiter, gender, age, and TSH levels were correlated with Tg.In adults from regions with adequate and more than adequate iodine intake, we found that Tg may be a suitable marker of iodine status; gender-specific Tg RI was unnecessary; there was no difference between Tg RIs in regions with adequate and more than adequate iodine intake; and the TSH criterion for selecting the Tg reference population could follow the local TSH reference rather than 0.5 to 2.0 mIU/L.

Progress in standardizing and harmonizing thyroid function tests

Iodine is an essential component of thyroid hormone. Because thyroid hormone synthesis is affected by iodine deficiency on the one hand and by excess iodine intake on the other, thyroid function biomarkers may be useful for assessing iodine status and studying the effects of iodine supplementation. However, reference intervals for some of the most useful thyroid function biomarkers, including serum concentrations of thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroglobulin, vary widely due to variability in the commercially available immunoassays for these tests. Recognizing the need for standardization of thyroid function testing, the International Federation of Clinical Chemistry and Laboratory Medicine established a working group, later restructured as the Committee for Standardization of Thyroid Function Tests, to examine its feasibility. The committee has established a conventional reference measurement procedure for FT4 and an approach to harmonization of results for TSH. Panels of single-donation human blood specimens that span the measuring interval of the immunoassays were used to assess the performance of commercially available immunoassays and form the basis for their recalibration. Recalibration of the manufacturers' methods for both FT4 and TSH has shown that the variability among immunoassays can be successfully eliminated for euthyroid individuals as well as for patients with thyroid disease. The committee is not investigating the standardization of thyroglobulin at the present time.

Transcriptome Profiling of Caco-2 Cancer Cell Line following Treatment with Extracts from Iodine-Biofortified Lettuce (Lactuca sativa L.)

Although iodization of salt is the most common method used to obtain iodine-enriched food, iodine deficiency disorders are still a global health problem and profoundly affect the quality of human life. Iodine is required for the synthesis of thyroid hormones, which are crucial regulators of human metabolism, cell growth, proliferation, apoptosis and have been reported to be involved in carcinogenesis. In this study, for the first time, we evaluated the effect of iodine-biofortified lettuce on transcriptomic profile of Caco-2 cancer cell line by applying the Whole Human Genome Microarray assay. We showed 1326 differentially expressed Caco-2 transcripts after treatment with iodine-biofortified (BFL) and non-fortified (NFL) lettuce extracts. We analysed pathways, molecular functions, biological processes and protein classes based on comparison between BFL and NFL specific genes. Iodine, which was expected to act as a free ion (KI-NFL) or at least in part to be incorporated into lettuce macromolecules (BFL), differently regulated pathways of numerous transcription factors leading to different cellular effects. In this study we showed the inhibition of Caco-2 cells proliferation after treatment with BFL, but not potassium iodide (KI), and BFL-mediated induction of mitochondrial apoptosis and/or cell differentiation. Our results showed that iodine-biofortified plants can be effectively used by cells as an alternative source of this trace element. Moreover, the observed differences in action of both iodine sources may suggest a potential of BFL in cancer treatment.

Tg in Adults as a Sensitive Biomarker of Iodine Status: A 5-Year Follow up Population Study in Different Levels of Iodine Intake Regions

This study was to evaluate the usefulness of serum thymoglobulin (Tg) in adults to assess iodine status through a 5-year cohort study which was conducted in three regions with different levels of iodine intake: mild deficiency, more than adequate, and excess, from 1999 to 2004 in China. A total of 3099 subjects over 14 years old with normal serum levels of Tg in 1999 were eligible, of whom 2448 were followed in 2004. Serum levels of thyroid hormones and thyroid autoantibodies as well as urine iodine were measured, and B-mode ultrasonography of the thyroid was performed. A general linear model was performed to determine the determinant factors of serum Tg. Among subjects with mildly deficient iodine intake, those with more than adequate intake, and those with excessive intake, the baseline levels of serum Tg were substantially different (7.5μg/L, 5.9μg/L, and 6.8μg/L respectively, P<0.01), which were associated with age, sex, the rate of positive TgAb, abnormal thyroid volume, abnormal TSH, and positive personal history of thyroid diseases. The data from 1856 subjects with normal range of thyroid parameters but no personal history of thyroid diseases were analyzed to clarify the effect of iodine intake on Tg. Among these three regions, the serum Tg levels were substantially different in both 1999 and 2004, with a similar pattern for increased Tg (ΔTg) (3.1μg/L, 2.5μg/L and 3.5μg/L respectively, P<0.01). The general linear model analysis revealed that age, Tg, and baseline TSH levels were the determinants of ΔTg besides iodine intake. In conclusion, serum Tg in adults, resulting from a time-accumulative effect of iodine exposure, is a useful biomarker of regional iodine intake.

The Relationship Between Iodine Intake and Serum Thyroglobulin in the General Population

The relationship is shown between a concentration of urinary iodine and serum thyroglobulin in population studies carried out on a general population that was randomly selected from the registry of the General Health Insurance Company (individuals aged 6-98 years, 1751 males, 2420 females). The individuals were divided into subgroups with a urinary iodine concentration of <50, 50-99, 100-199, 200-299 and ≥300 μg/l. The mean and median of thyroglobulin were calculated in these subgroups. Tg concentrations were dependent on gender (males<females), age (thyroglobulin increased with age) and statistically significant negative relationship was observed between thyroglobulin and urinary iodine in individuals with urinary iodine <300 μg/l and the age under 65 years. Upper nonparametric tolerance limits of thyroglobulin in relation to iodine intake were calculated in subgroup of normal individuals (n=1858, thyroglobulin, urinary iodine, thyrotropin and free thyroxine were within the normal reference range). Upper limits were dependent on gender and age. The total value of upper limits is 44 μg/l; for individuals aged 6-17 years it is 39.1 μg/l; 18-65 years = 51.4 μg/l and 66-98 years = 60.6 μg/l. In general, thyroglobulin serum concentrations higher than 40 μg/l should be an indicator for determining urinary iodine.

The comparison of thyroxine versus thyroxine plus oral iodine in the treatment of congenital hypothyroidism due to iodine deficiency

AIM

Iodine deficiency is one of the most important causes of congenital hypothyroidism. In addition to thyroid hormone replacement, iodine supplementation is also given to newborns with congenital hypothyroidism due to iodine deficiency. We aimed to determine whether it is beneficial to administer iodine supplementation in addition to the L-thyroxine (L-T4) treatment of newborns with congenital hypothyroidism due to iodine deficiency.

MATERIALS AND METHODS

Of 51 newborns, 26 who were diagnosed with congenital hypothyroidism due to iodine deficiency were treated with L-T4. The remaining 25 cases were given L-T4 plus 100 μg/day of oral iodine. Free triiodothyronine (fT3), free thyroxine (fT4), thyroid-stimulating hormone (TSH), thyroglobulin (TG), thyroid volume, urine iodine and breast milk iodine levels were measured in the first and third months of treatment, and the data were compared between the two groups.

RESULTS

First- and third-month values of fT3, fT4, TSH, TG and thyroid volume for both groups were statistically similar. There was no significant difference between the two groups in respect to falling levels of fT3 and TSH, the rate of increase of fT4 levels or the shrinkage rate of thyroid volume.

CONCLUSION

In this study, the addition of oral iodine to L-T4 treatment provided no benefit compared to treatment with L-T4 alone.

Elevated Serum Thyroglobulin and Low Iodine Intake Are Associated with Nontoxic Nodular Goiter among Adults Living near the Eastern Mediterranean Coast

Background. Information about iodine intake is crucial for preventing thyroid diseases. Inadequate iodine intake can lead to thyroid diseases, including nontoxic nodular goiter (NNG). Objective. To estimate iodine intake and explore its correlation with thyroid diseases among Israeli adults living near the Mediterranean coast, where iodine-depleted desalinated water has become a major source of drinking water. Methods. Cross-sectional study of patients attending Barzilai Medical Center Ashkelon. Participants, who were classified as either NNG (n = 17), hypothyroidism (n = 14), or control (n = 31), provided serum thyroglobulin (Tg) and completed a semiquantitative iodine food frequency questionnaire. Results. Elevated serum Tg values (Tg > 60 ng/mL) were significantly more prevalent in the NNG group than in the other groups (29% versus 7% and 0% for hypothyroidism and controls, resp., P < 0.05). Mean estimated iodine intake was significantly lower in the NNG group (65 ± 30 μg/d) than in controls (115 ± 60 μg/d) (P < 0.05) with intermediate intake in the hypothyroid group (73 ± 38 μg/d). Conclusions. Elevated serum Tg values and low dietary iodine intake are associated with NNG among adult patients in Ashkelon District, Israel. Larger studies are needed in order to expand on these important initial findings.

Thyroglobulin as a biomarker of iodine deficiency: a review

BACKGROUND

Thyroglobulin, produced exclusively by the thyroid gland, has been proposed to be a more sensitive biomarker of iodine status than thyrotropin or the thyroid hormones triiodothyronine and thyroxine. However, evidence on the usefulness of thyroglobulin (Tg) to assess iodine status has not been extensively reviewed, particularly in pregnant women and adults.

SUMMARY

An electronic literature search was conducted using the Cochrane CENTRAL, Web of Science, PubMed, and Medline to locate relevant studies on Tg as a biomarker of iodine status. Since urinary iodine concentration (UIC) is the recommended method to assess iodine status in populations, only studies that clearly reported both Tg and UIC were included. For the purpose of this review, a median Tg <13 μg/L and a median UIC ≥100 μg/L (UIC ≥150 μg/L for pregnant women) were used to indicate adequate iodine status. We excluded studies conducted in subjects with either known thyroid disease or those with thyroglobulin antibodies. The search strategy and selection criteria yielded 34 articles of which nine were intervention studies. The majority of studies (six of eight) reported that iodine-deficient pregnant women had a median Tg ≥13 μg/L. However, large observational studies of pregnant women, including women with adequate and inadequate iodine status, as well as well-designed intervention trials that include both Tg and UIC, are needed. In adults, the results were equivocal because iodine-deficient adults were reported to have median Tg values of either <13 or ≥13 μg/L. Only studies in school-aged children showed that iodine-sufficient children typically had a median Tg <13 μg/L. Some of the inconsistent results may be partially explained by the use of different methodological assays and failure to assess assay accuracy using a certified reference material.

CONCLUSIONS

These data suggest that Tg does hold promise as a biomarker of iodine deficiency. However, it is associated with limitations. A median Tg cutoff of 13 μg/L warrants further investigation, particularly in adults or pregnant women, as there is a lack of both observational and intervention studies in these groups.

Iodine and thyroid function

Severe iodine deficiency causes hypothyroidism that results in impaired somatic growth and motor development in children. Mild and moderate iodine deficiencies cause multifocal autonomous growth of thyroid, which results in thyrotoxicosis. On the other hand, iodine excess is associated with the development of hypothyroidism and thyroid autoimmunity. In areas of iodine deficiency, a sudden increase in iodine intake is associated with transient hyperthyroidism. Recent studies demonstrated that long-term thyroid function of subjects who experienced both iodine deficiency and iodine excess during childhood tended to be abnormal despite optimization of their current iodine intake. Iodine status in the Korean Peninsula is very unique because people in the Republic of Korea have been shown to have predominantly excessive iodine levels, whereas the Democratic People's Republic of Korea is known to be an iodine-deficient area. Further research is warranted to verify the optimal ranges of iodine intake and to clarify the effects of iodine intake on thyroid disorders in the Korean Peninsula.

Assessment of iodine status in children, adults, pregnant women and lactating women in iodine-replete areas of China

BACKGROUND

Iodine deficiency disorders (IDD) are widespread in China. Presently, IDD have been put under control by Universal Salt Iodisation (USI) in China; however, there is a lack of evidence on whether the iodine status in adults, pregnant women and lactating women is optimal. This study was therefore conducted to assess the iodine nutrition and thyroid function of children, adults, pregnant women and lactating women residing in areas where the USI program is fully established.

DESIGN

Six areas were selected according to the geographical regions in China. In each of these areas, we selected 4 distinct groups of subjects (children, adults, pregnant women and lactating women) in regions where the coverage rate of iodised salt was more than 95% and the levels of iodine and fluoride in drinking water were less than or equal to 10 µg/L and 1 mg/L, respectively. We tested the iodine content of salt, urinary iodine (UI), free thyroxin (FT4), thyrotropin (TSH), thyroglobulin (Tg), thyroglobulin antibody (Tg-Ab) and antimicrosomal antibody (TM-Ab) in the 4 groups, and examined the thyroid volume in children.

RESULTS

The median urinary iodine (MUI) concentrations were 271.4 μg/L, 260.2 μg/L, 205.9 μg/L and 193.9 μg/L in children, adults, pregnant women and lactating women, respectively; MUI in children and adults were more than adequate. The goitre prevalence (GP) in children was 6.70%. The odds ratios (OR) of subclinical hypothyroidism in the Tg-Ab- or TM-Ab-positive groups were 3.80, 7.65, 2.01 and 7.47 for children, adults, pregnant women and lactating women, respectively, compared with the negative groups.

CONCLUSIONS

The iodine status in children and adults is above the requirement, we should reduce their iodine intake. Subclinical hypothyroidism easily occurs in the Tg-Ab or TM-Ab positive groups.

Factors associated with serum thyroglobulin levels in a population living in Belarus

OBJECTIVE

Serum thyroglobulin (Tg) has been associated with a number of thyroid disorders and has been proposed as an indicator of iodine deficiency in a population. However, few studies have addressed the epidemiology of Tg in a population-based setting or in the context of exposure to radioactive iodine-131 (I-131). Our objective was to evaluate baseline levels of Tg in relation to sociodemographic characteristics, iodine status and thyroid function for individuals exposed to I-131.

DESIGN

A population-based cohort assembled in Belarus following the Chornobyl accident provided demographic factors, clinical data and physiological measurements.

PARTICIPANTS

Our analytical sample included 10,344 subjects of whom 7890 had no thyroid disease and 2454 had evidence of structural or functional thyroid abnormality.

MEASUREMENTS

Standardized assays were used to measure serum Tg, urinary iodine, TSH and antibodies to Tg and thyroid peroxidase. Ultrasound was used to assess the presence of nodules and estimate thyroid volume.

RESULTS

In the fully adjusted model, percent change in Tg was significantly increased among females, smokers and subjects of older age and Tg increased with decreasing urinary iodine concentration, increasing serum TSH and increasing thyroid volume (P-values for trend <0·0001), and presence of thyroid nodules (P < 0·05). We found a complex interaction between region of residence, rural/urban living, presence/absence of thyroid abnormalities and serum Tg (P < 0·0001).

CONCLUSIONS

In residents of Belarus, serum Tg is significantly related to presence of thyroid abnormalities as well as indicators of thyroid function and iodine deficiency and, therefore, could be used to characterize the iodine status and thyroid function of individuals in the context of epidemiological study.

Differences between subjects with sufficient and deficient urinary iodine in an area of iodine sufficiency

BACKGROUND

Iran has long been recognized as a country of iodine sufficiency; however, recent studies show that the proportion of subjects with insufficient urinary iodine is gradually increasing in Tehran capital city.

AIM

The aim of this study was to evaluate differences between individuals with sufficient and deficient urinary iodine in Tehran.

MATERIAL AND METHODS

In this cross-sectional study, 639 Tehranian adult subjects, aged ≥ 19 yr (242 males, 397 females), were enrolled through randomized cluster sampling. A 24-h urine sample was collected for measurement of urinary iodine, sodium and creatinine concentrations using the digestion method, flame photometry and autoanalyzer assay, respectively. Salt intake was estimated and iodine content of household salt was measured by titration.

RESULTS

Medians (interquartile range) of 24-h urinary iodine concentrations in subjects with sufficient and deficient urinary iodine were 163.0 (126.0-235.0) and 44.0 (26.0-67.0) μg/l, p<0.001, respectively. Salt with iodine content of >20 parts per million was consumed by 77.4 and 38.3% of subjects with sufficient and deficient urinary iodine, respectively (p<0.001). Median daily salt intake in subjects with sufficient urinary iodine was significantly higher than in those with deficient urinary iodine (8.1 vs 7.3 g, p<0.001). No significant differences in the mentioned variables were observed between males and females. Fifty and 30% of subjects with insufficient and sufficient urinary iodine had <7 yr education, respectively (p<0.001).

CONCLUSIONS

Iodine content of salt, the amount of salt intake and education levels differ greatly between subjects with sufficient and deficient urinary iodine in Tehran.

Levothyroxine treatment in pregnancy: indications, efficacy, and therapeutic regimen

The prevalence of overt and subclinical hypothyroidism during pregnancy is estimated to be 0.3–0.5% and 2–3%, respectively. Thyroid autoantibodies are found in 5–18% of women in the childbearing age. The aim of this review is to underscore the clinical significance of these findings on the health of both the mother and her offspring. Methods of evaluation of thyroid function tests (TFTs) during pregnancy are described as are the threshold values for the diagnosis of overt and subclinical hypothyroidism or hypothyroxinemia. Anticipated differences in TFTs in iodine-sufficient and iodine-deficient areas are discussed and data are provided on potential complications of hypothyroidism/hypothyroxinemia and autoimmune thyroid disease during pregnancy and adverse effects for the offspring. The beneficial effects of levothyroxine therapy on pregnancy outcomes and offspring development are discussed with a proposed treatment regimen and follow up strategy.