Reciprocal changes of serum thyroglobulin and TSH in residents of a moderate endemic goitre area

Adverse effects on thyroid of Chinese children exposed to long-term iodine excess: optimal and safe Tolerable Upper Intake Levels of iodine for 7- to 14-y-old children

Background

The adverse effects of iodine excess on the thyroid in children are not well understood, and the Tolerable Upper Intake Level for iodine in children is unclear.

Objective

The aims of this study were to assess the effects of chronic long-term iodine excess on thyroid function in children and to explore the safe Tolerable Upper Intake Level of iodine in Chinese children.

Design

A multistage cross-sectional study was conducted in 2224 children from areas with adequate to excessive iodine content in drinking water. Repeated samples of 24-h urine and spot urine samples were collected to estimate habitual daily iodine intakes of children. The thyroid volume in children was measured and blood samples were collected to determine thyroid function.

Results

The habitual iodine intake of children was 298 μg/d (range: 186-437 μg/d). The total goiter rate was 9.7%, 232 (11.2%) children had hyperthyrotropinemia, and 232 (11.2%) children had thyroglobulin (Tg) concentrations >40 μg/L. The prevalence of hyperthyrotropinemia was >10% in children at iodine intakes of 200-300 μg/d. Tg concentrations increased with increased iodine intake (β = 0.5; 95% CI: 0.4, 0.6), and the prevalence of Tg >40 μg/L was >3% in all iodine-intake groups. Multivariate logistic regression analysis indicated that the risk of total goiter significantly increased at iodine intakes ≥250-299 μg/d in 7- to 10-y-old children (OR: 8.8; 95% CI: 2.3, 34.0) and at iodine intakes ≥300-399 μg/d in 11- to 14-y-old children (OR: 5.2; 95% CI: 1.5, 18.3). However, there were no consistent differences in the risk of hyperthyrotropinemia and Tg >40 μg/L in children between different iodine-intake groups.

Conclusions

Thyroid volume and goiter appear to be more sensitive indicators of thyroid stress than thyrotropin and Tg in children with long-term excess iodine intakes. We recommend 250 and 300 μg/d as safe Tolerable Upper Intake Levels of iodine for children aged 7-10 y and 11-14 y, respectively. This trial was registered at www.clinicaltrials.gov as NCT02915536.

Factors associated with serum thyroglobulin in a Ukrainian cohort exposed to iodine-131 from the accident at the Chernobyl Nuclear Plant

BACKGROUND

Serum thyroglobulin (Tg) is associated with the presence of thyroid disease and has been proposed as a biomarker of iodine status. Few studies have examined factors related to serum Tg in populations environmentally exposed to ionizing radiation and living in regions with endemic mild-to-moderate iodine deficiency.

METHODS

We screened 10,430 individuals who were living in Ukraine and under 18 years of age at the time of the 1986 Chernobyl Nuclear Power Plant accident for thyroid disease from 2001 to 2003. We estimated the percent change (PC) in serum Tg associated with demographic factors, iodine-131 thyroid dose, and indicators of thyroid structure and function using linear regression. We also examined these relationships for individuals with and without indications of thyroid abnormality.

RESULTS

Mean and median serum Tg levels were higher among participants with abnormal thyroid structure/function. Percent change in serum Tg increased among females, smokers and with older age (p-values<0.001), and Tg increased with increasing thyroid volume, and serum thyrotropin (p-values for trend<0.001). We found no evidence of significant associations between iodine-131 thyroid dose and Tg. Serum Tg levels were inversely associated with iodized salt intake (PC=-7.90, 95% confidence interval: -12.08, -3.52), and over the range of urinary iodine concentration, the odds of having elevated serum Tg showed a U-shaped curve with elevated Tg at low and high urinary iodine concentrations.

CONCLUSION

Serum Tg may be a useful indicator of population iodine status and a non-specific biomarker of structural and functional thyroid abnormalities in epidemiological studies.

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.

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

OBJECTIVE

Our objective was to investigate individual serum thyroglobulin (Tg) changes in relation to iodine fortification (IF) and to clarify possible predictors of these changes.

DESIGN

We performed a longitudinal population-based study (DanThyr) in two regions with different iodine intake at baseline: Aalborg (moderate iodine deficiency (ID)) and Copenhagen (mild ID). Participants were examined at baseline (1997) before the mandatory IF of salt (2000) and again at follow-up (2008) after IF.

METHODS

We examined 2465 adults and a total of 1417 participants with no previous thyroid disease and without Tg-autoantibodies were included in the analyses. Serum Tg was measured by immunoradiometric method. We registered participants with a daily intake of iodine from supplements in addition to IF.

RESULTS

Overall, the follow-up period saw no change in median Tg in Copenhagen (9.1/9.1 μg/l, P=0.67) while Tg decreased significantly in Aalborg (11.4/9.0 μg/l, P<0.001). Regional differences were evident before IF (Copenhagen/Aalborg, 9.1/11.4 μg/l, P<0.001), whereas no differences existed after IF (9.1/9.0 μg/l, P=1.00). Living in Aalborg (P<0.001) and not using iodine supplements at baseline (P=0.001) predicted a decrease in Tg whereas baseline thyroid enlargement (P=0.02) and multinodularity (P=0.01) were associated with an individual increase in Tg during follow-up.

CONCLUSIONS

After IF we observed a decrease in median Tg in Aalborg and the previously observed regional differences between Aalborg and Copenhagen had levelled out. Likewise, living in Aalborg was a strong predictor of an individual decrease in serum Tg. Thus, even small differences in iodine intake at baseline were very important for the individual response to IF.

Subclinical Hypothyroidism and Elevated Thyroglobulin in Infants with Chronic Excess Iodine Intake

BACKGROUND

Acute iodine excess in newborns can cause hypothyroidism, but there are limited data on the effects of iodine excess on thyroid function in older infants. The aim of this study was to measure the effects of chronic excess iodine intake on thyroid function in 6-24-month-old infants.

METHODS

In this cross-sectional study, infants (n=696) in eastern Nepal were studied. Spot urine samples, venous blood samples, and household salt samples were collected, and urinary iodine concentration (UIC), serum free thyroxine (fT4), thyrotropin (TSH), thyroglobulin (Tg), and titrated household salt iodine concentration (SIC) were measured. Daily iodine intake was calculated from UIC based on estimates of urine volume at this age.

RESULTS

Median (25th-75th percentile) household SIC was 89 (70-149) ppm, while national legislation stipulates a fortification level of 50 ppm. Median UIC was 407 (312-491) μg/L; 76% of infants had a UIC >300 μg/L, suggesting iodine excess. Calculated mean iodine intake in 12-24-month-old infants was 220 μg/day, exceeding the recommended safe upper limit for iodine at this age (200 μg/day). Among the infants, 15.8% had an elevated Tg, 7.4% had subclinical hypothyroidism, but <1% had overt hypothyroidism. UIC was not a significant predictor of thyroid function, thyroid hormones, or Tg.

CONCLUSION

In 6-24-month-old infants exposed to excessive iodine intake, ∼7% have subclinical hypothyroidism but <1% have overt hypothyroidism. These findings suggest the thyroid in late infancy is already able to adapt to high iodine intakes and, in most cases, maintain euthyroidism.

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.

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.

The effect of voluntary iodine prophylaxis in a small rural community: the Pescopagano survey 15 years later

CONTEXT

Iodine deficiency disorders are a major public health problem, and programs have been implemented to improve iodine nutrition.

OBJECTIVE

The objective of the study was to verify the effects of voluntary iodine prophylaxis in a small rural community (Pescopagano, Italy).

DESIGN

The design of the study was the evaluation of the prevalence of thyroid disorders 15 years after a previous survey conducted before iodine prophylaxis.

SETTING

The setting for this study was a general community survey.

PARTICIPANTS

One thousand one hundred forty-eight residents were examined in 2010 and 1411 in 1995.

RESULTS

In 2010, 757 of 1148 subjects (65.9%) routinely used iodized salt, urinary iodine excretion being significantly higher than in 1955 (median 98.0 μg/L, vs 55.0 μg/L, P < .0001). The prevalence of goiter was lower in 2010 than in 1995 (25.8% vs 46.1%, P < .0001), mainly due to the reduction of diffuse goiter (10.3% vs 34.0%, P < .0001). In 2010 vs 1995, thyroid autonomy in subjects younger than 45 years old (3 of 579, 0.5% vs 25 of 1010, 2.5% P = .004) and nonautoimmune hyperthyroidism in subjects older than 45 years old (8 of 569, 1.4% vs 18 of 401, 4.5%, P = .03) were less frequent. The prevalence of hypothyroidism was higher in 2010 vs 1995 (5.0% vs 2.8%, P = .005), mainly because of an increased frequency of subclinical hypothyroidism in subjects younger than 15 years old (7 of 83, 8.4% vs 0 of 419, 0.0%, P < .0001). Accordingly, serum thyroid autoantibodies (19.5% vs 12.6%; P < .0001) and Hashimoto's thyroiditis (14.5% vs 3.5%; P < .0001) were more frequent in 2010 than in 1995.

CONCLUSIONS

In the present work, the role of voluntary iodine prophylaxis was assessed in a small rural community relatively segregated, in which genetic and other environmental factors have not substantially changed between the 2 surveys. Iodine intake strongly affected the pattern of thyroid diseases, but the benefits of correcting iodine deficiency (decreased prevalence of goiter and thyroid autonomy in younger subjects and reduced frequency of nonautoimmune hyperthyroidism in older subjects) far outweighs the risk of development of thyroid autoimmunity and mild hypothyroidism in youngsters.

Serum TSH and risk of papillary thyroid cancer in nodular thyroid disease

CONTEXT

TSH is the main factor involved in the control of proliferation of thyrocytes. Recently, a strong relationship between serum TSH and risk of thyroid malignancy has been reported.

OBJECTIVES

The aim was to review published papers about the relationship between serum TSH and frequency of differentiated thyroid cancer.

EVIDENCE ACQUISITION

PubMed was used to identify studies focused on the relationship between TSH and differentiated thyroid cancer.

EVIDENCE SYNTHESIS

In patients with nodular thyroid disease, the risk of thyroid malignancy increases with serum TSH, and even within normal ranges, higher TSH values are associated with a higher frequency and more advanced stage of thyroid cancer. The likelihood of papillary thyroid carcinoma is reduced when TSH is lower, as in thyroid autonomy, and increased when TSH is higher, as in thyroid autoimmunity. Treatment with l-thyroxine (LT4), which reduces serum TSH, is associated with significantly lower risk of developing clinically detectable thyroid cancer.

CONCLUSIONS

TSH plays a key role in the development of clinically detectable thyroid cancer, and LT4 treatment reduces the risk of thyroid malignancy in patients with nodular thyroid disease. According to the guidelines of the main scientific societies, LT4 therapy is not currently recommended for the treatment of patients with nodular goiter. Even if the available data are not sufficient to advise LT4 treatment in all patients with nodular goiter with the aim of reducing the risk of papillary thyroid carcinoma, we propose that this indication should be reconsidered, taking into account recent evidence reported in the literature.

Radioiodine 131I treatment for large nodular goiter: recombinant human thyrotropin allows the reduction of radioiodine 131I activity to be administered in patients with low uptake

BACKGROUND

(131)I therapy is effective in reducing the volume of large nodular goiters (thyroid volume [TV]), mainly after stimulation with recombinant human thyrotropin (rhTSH). The amount of (131)I to be administered inversely depends on thyroid radioactive iodine uptake (RAIU). In patients with low RAIU, we evaluated the efficacy of (131)I treatment at lower doses with respect to those calculated on the basal RAIU, after rhTSH stimulation.

METHODS

Eighteen consecutive patients (17 women and 1 man, 49-83 years) with large nodular goiter were included in the study. At enrollment, 24th h RAIU, TSH, free thyroxine, free triiodothyronine, thyroglobulin antibodies, thyroid peroxidase antibodies, TSH receptors antibodies, urinary iodine, and TV were measured. RAIU was <40% in 11 patients (lower uptake group [LUG]) and >40% in 7 (higher uptake group [HUG]). RAIU difference in the two groups was significant (p < 0.0001). LUG patients were treated with rhTSH (0.03 mg i.m.) and RAIU was measured again after 24 hours. The administered amount of (131)I was aimed to give the thyroid a dose of 100 Gy, by the formula: (131)I activity = 370 MBq × TV (mL)/RAIU(%), taking into account RAIU value after rhTSH for LUG patients. Patients were re-evaluated 3 and 12 months after therapy.

RESULTS

At enrollment, LUG and HUG patients did not differ for TV, free thyroxine, free triiodothyronine, TSH, and urinary iodine. LUG patients were older than HUG patients (p = 0.027). In LUG, the uptake increased after rhTSH (42.8% [36%-47.5%] vs. 30% [23.4%-31.6%], p = 0.0044). The (131)I activity was 1073 MBq (740-1103 MBq) in LUG and 851 MBq (677-918 MBq) in HUG (p = 0.22, NS), vs. 1300 MBq (1077-2150 MBq) in LUG, based on RAIU before rhTSH. At 3 and 12 months after radioiodine, TV was reduced to 74% [59%-84%] and 53% [42%-72%] in LUG and 75% [70%-77%] and 65% [54%-74%] in HUG, respectively. The reduction was significant with respect to the basal, both at 3 and 12 months, but not different between the two groups.

CONCLUSIONS

One single dose of 0.03 mg of rhTSH increased the thyroid RAIU by 40% in patients with nodular goiter and low basal uptake. This allowed a mean reduction of 36% (26%-42%) in the administered (131)I activity without loss of effectiveness. In patients with low RAIU, rhTSH pre-treatment may optimize (131)I therapy.

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

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 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.

Goitre and iodine deficiency in Afghanistan: a case-control study

I deficiency is the leading cause of preventable mental retardation. A number of surveys in Afghanistan show goitre prevalence rates more than 20 % amongst children and women. Access to iodised salt remains low, with disparate coverage by region, despite the recent implementation of a national salt iodisation programme. The objectives were to identify whether the presence of goitre is a satisfactory marker of I deficiency and to examine the relationship between goitre and thyroid function. A case-control study was carried out in children and women of childbearing age, stratified on the presence of goitre. Adequate levels of urinary I were observed in 6.8 % of all the subjects, and amongst the subjects without goitre, this figure was only 9 %. The presence of goitre was significantly associated with severe urinary I deficiency; however, the difference between the cases and controls was not as great as expected. An association between the presence of goitre and elevated thyroid-stimulating hormone (TSH) levels was observed, but 14 % of the children without palpable goitre also showed abnormal TSH levels.Given that the majority of subjects showed some degree of I deficiency and that children without goitre may have elevated TSH levels, the absence of goitre is an insufficient indicator to determine adequate I status. The risk of subsequent development of goitre, in the currently non-goitre population, is elevated. This suggests that short-term I supplementation should be considered independently of the presence of goitre or urinary I level, until the access to and consumption of iodised salt is generalised.

Development of a dried whole-blood spot thyroglobulin assay and its evaluation as an indicator of thyroid status in goitrous children receiving iodized salt

BACKGROUND

Serum thyroglobulin appears to be a sensitive marker of thyroid dysfunction in endemic goiter. However, its value as an indicator of thyroid status in children after the introduction of iodized salt has not been tested.

OBJECTIVE

The objective was to optimize and validate a thyroglobulin assay on dried whole blood spots and to evaluate thyroglobulin as an indicator of thyroid response to iodized salt.

DESIGN

A standardized, commercially available, sandwich fluoroimmunometric serum thyroglobulin assay was adapted for use on blood spots and validated in Swiss children. In a 1-y prospective study in 377 goitrous Moroccan children aged 6-15 y, the assay was used to measure thyroglobulin before and after the introduction of iodized salt. Urinary iodine, thyroid volume, thyrotropin, and thyroxine were measured, and regression was done with thyroglobulin as the dependent variable.

RESULTS

Correlation between the blood spot and serum assays was excellent (r = 0.98). The SD of the difference between the blood spot and serum assays was 3.8 micro g/L; the median CVs for the blood spot assay in controls and samples were 6.3% and 14.4%, respectively. Median thyroglobulin was 24.5 (range: 0-328.8) micro g/L at baseline and fell significantly after the introduction of iodized salt to 6.2 (0-83.1) and 4.4 (0-47.1) micro g/L at 5 and 12 mo, respectively (P < 0.0001). Regression of urinary iodine and thyroid volume on thyroglobulin was highly significant at baseline and at 5 mo (P < 0.001).

CONCLUSION

Thyroglobulin, measured in dried whole blood spots, may be a valuable indicator of improving thyroid function in children after supplementation with iodized salt.

Multinodular goitre: 'much more to it than simply iodine deficiency'

For over a century, multinodular goitre (MNG) has been looked upon as the simple consequence of iodine deficiency. This view is now no longer tenable. Indeed, many characteristics of MNG do not fit with the iodine deficiency concept. For example, nodular goitre is a frequent disease even in those countries where the population is never exposed to iodine shortage. Moreover, neither multinodularity, nor the proverbial heterogeneity of growth and function or the autonomous, thyroid stimulating hormone (TSH)-independent growth of many goitres are compatible with the iodine deficiency concept, let alone subclinical or overt thyrotoxicosis which often complicates the course of a MNG. Recent investigations have led to the conclusion that MNGs are true benign neoplasias that are due to the high intrinsic growth potential of a variable, genetically predetermined fraction of all thyrocytes. Gross and heritable metabolic and functional differences between the individual thyrocytes, from which new follicles are generated during goitrogenesis, are the cause of the often spectacular functional and structural heterogeneity of MNG. Superimposed iodine deficiency changes the epidemiology, but not the basic mechanisms of goitrogenesis. These new pathogenetic concepts have a profound impact on the clinical management of MNG.

Circulating thyroglobulin transcytosed by thyroid cells in complexed with secretory components of its endocytic receptor megalin

After its endocytosis from the colloid, some thyroglobulin (Tg) is transcytosed intact across thyrocytes, accounting in part for its presence in the circulation. We previously showed that megalin (gp330), an endocytic Tg receptor, mediates apical to basolateral Tg transcytosis. Here we investigated whether a portion of megalin remains combined with Tg after its transcytosis, using studies with cultured thyroid cells and in vivo observations. FRTL-5 cells, a rat thyroid cell line, cultured on filters in dual chambers form tight junctions and exhibit features of polarity, with expression of megalin exclusively on the upper (apical) surface. After the addition of unlabeled Tg to the upper chamber and incubation at 37 C, some Tg was transcytosed intact across FRTL-5 cells into the lower chamber. Two antimegalin ectodomain antibodies precipitated transcytosed Tg in fluids collected from the lower chamber. After the addition of Tg to surface-biotinylated FRTL-5 cells, an anti-Tg antibody and the two antimegalin ectodomain antibodies precipitated high molecular mass biotinylated material in fluids collected from the lower chamber, corresponding to much of the megalin ectodomain, as well as smaller amounts of lower molecular mass material. The results indicate that Tg transcytosed across FRTL-5 cells remains complexed with megalin ectodomain components, which we refer to as megalin secretory components. In aminotriazole-treated rats, which develop increased megalin-mediated Tg transcytosis, antimegalin antibodies precipitated some of the Tg in the serum. Tg was also precipitated by antimegalin antibodies in sera from patients with Graves' disease, in which we found increased megalin expression on the apical surface of thyrocytes. In contrast, in thyroidectomized patients with metastatic papillary thyroid carcinoma, in whom Tg is directly secreted by neoplastic thyroid cells into the circulation rather than transcytosed, serum Tg was not precipitated by antimegalin antibodies. The detection of Tg-megalin complexes may help identify the source of serum Tg in patients with thyroid diseases.

Hot microscopic areas of iodine-deficient euthyroid goitres contain constitutively activating TSH receptor mutations

Constitutively activating TSH receptor mutations have been established as the most common molecular basis for the pathogenesis of toxic thyroid nodules. These mutations result in uncontrolled signalling through the TSH receptor that is likely to cause hyperfunction and proliferation. The incidence of toxic multinodular goitres has been demonstrated to be related to iodine deficiency. Moreover, scintigraphically autonomous areas are found in 40% of euthyroid goitres from iodine-deficient areas. To investigate the molecular cause of these autonomous areas, small autoradiographically hot areas were examined for somatic TSH receptor mutations using archival tissue sections from 14 patients with euthyroid goitres, which had been originally prepared nearly 20 years ago. All patients had received (125)I 17 h preoperatively for the autoradiographic investigation of their thyroid. Areas with high and low (125)I-labelling on autoradiography sections were collected separately either from serial paraffin-embedded tissue sections, or Eukitt-embedded tissue sections containing the autoradiograph. After genomic DNA extraction, the transmembrane segment of the TSH receptor was PCR-amplified and directly sequenced. Somatic TSH receptor mutations were identified in areas with high (125)I-labelling in four patients: A623I, L629P, F631L, and T632I. This is the first evidence that TSH receptor mutations occur in microscopic areas with increased (125)I-labelling in euthyroid goiters and it suggests that TSH receptor mutations in these areas confer the potential to develop into toxic thyroid nodules. It is therefore very likely that toxic thyroid nodules originate from small autonomous areas in iodine-deficient euthyroid goitres that contain a TSH receptor mutation.

Role of megalin (gp330) in transcytosis of thyroglobulin by thyroid cells. A novel function in the control of thyroid hormone release

When thyroglobulin (Tg) is endocytosed by thyrocytes and transported to lysosomes, thyroid hormones (T4 and T3) are released. However, some internalized Tg is transcytosed intact into the bloodstream, thereby avoiding proteolytic cleavage. Here we show that megalin (gp330), a Tg receptor on thyroid cells, plays a role in Tg transcytosis. Following incubation with exogenous rat Tg at 37 degrees C, Fisher rat thyroid (FRTL-5) cells, a differentiated thyroid cell line, released T3 into the medium. However, when cells were incubated with Tg plus either of two megalin competitors, T3 release was increased, suggesting that Tg internalized by megalin bypassed the lysosomal pathway, possibly with release of undegraded Tg from cells. To assess this possibility, we performed experiments in which FRTL-5 cells were incubated with either unlabeled or (125)I-labeled Tg at 37 degrees C to allow internalization, treated with heparin to remove cell surface-bound Tg, and further incubated at 37 degrees C to allow Tg release. Intact 330-kDa Tg was released into the medium, and the amount released was markedly reduced by megalin competitors. To investigate whether Tg release resulted from transcytosis, we studied FRTL-5 cells cultured as polarized layers with tight junctions on permeable filters in the upper chamber of dual chambered devices. Following the addition of Tg to the upper chamber and incubation at 37 degrees C, intact 330-kDa Tg was found in fluids collected from the lower chamber. The amount recovered was markedly reduced by megalin competitors, indicating that megalin mediates Tg transcytosis. We also studied Tg transcytosis in vivo, using a rat model of goiter induced by aminotriazole, in which increased release of thyrotropin induces massive colloid endocytosis. This was associated with increased megalin expression on thyrocytes and increased serum Tg levels, with reduced serum T3 levels, supporting the conclusion that megalin mediates Tg transcytosis. Tg transcytosis is a novel function of megalin, which usually transports ligands to lysosomes. Megalin-mediated transcytosis may regulate the extent of thyroid hormone release.

Thyroglobulin in serum as an indicator of iodine status during pregnancy

Serum thyroglobulin and thyrotropin as well as urinary iodine concentrations were measured in healthy, pregnant Swedish (n=27) and Sudanese (n=21) women and the results compared with those of healthy Swedish (n=14) and Sudanese (n=20) non-pregnant controls. The median thyroglobulin concentrations (and interquartile range) in the Swedish pregnant women for the three trimesters were 15.5 (8-24), 10.5 (7-19) and 18.0 (13-25) microg/L, respectively. The median third trimester concentration was higher than both the first and second trimester concentrations, respectively (p<0.0001, p<0.0001). Compared to the control group, the Swedish pregnant women had a significantly higher median thyroglobulin concentration in the third trimester (p<0.05). Among the Sudanese pregnant women, the median serum thyroglobulin concentrations (and interquartile range) were 27.5 (12-40), 25.0 (15-43) and 30.0 (15-67) microg/L during the first, second and third trimesters, respectively. There were no significant differences between these concentrations. Compared to the control group, the Sudanese pregnant women had a significantly higher median thyroglobulin in the third trimester (p<0.01). The Sudanese pregnant women also showed significantly higher median thyroglobulin concentrations than the Swedish pregnant women in all the three trimesters of pregnancy (p<0.05, p<0.001 and p<0.01, respectively). However, there were no significant differences between the two non-pregnant controls. Among the Swedish pregnant women, 40%, 23% and 30% of the subjects showed serum thyroglobulin concentrations above 20 microg/ L during the first, second and third trimesters of pregnancy, respectively. Corresponding figures for the Sudanese pregnant women were 55%, 61% and 64%, respectively. A significantly negative correlation was shown between serum thyroglobulin and urinary iodine concentrations during the second and third trimesters in the Swedish women (r= -0.8, p=0.01 and r= -0.5, p=0.03, respectively), and in the third trimester in the Sudanese women (r= -0.6, p=0.03). No such correlation was observed between thyrotropin and urinary iodine concentration in either the Swedish or the Sudanese pregnant women. It is concluded that serum thyroglobulin is a more sensitive indicator of iodine deficiency than serum thyrotropin during pregnancy.

Thyroid diseases in the elderly

The ageing thyroid is associated with a number of morphological and functional changes, such as decreased serum T3 and mean thyroid-stimulating hormone concentrations, that are to some extent independent of intercurrent non-thyroidal illnesses. All thyroid diseases, including clinical and subclinical hypo- and hyperthyroidism, non-toxic nodular goitre and thyroid cancer, are encountered in the elderly, but their prevalence and clinical expression differ from those observed in younger patients. In the elderly, autoimmune hypothyroidism is particularly prevalent, hyperthyroidism is mainly characterized by cardiovascular symptoms and is frequently due to toxic nodular goitres, and differentiated thyroid carcinoma is more aggressive. The interpretation of thyroid function tests is difficult in old individuals, because of age-associated changes in thyroid function and frequent alterations secondary to non-thyroidal illnesses and/or drugs. Treatment of thyroid disease deserves special attention in old patients because of the increased risk of complications.

Endemic goiter and thyroid function in central-southern Sardinia. Report on an extensive epidemiological survey

Although the existence of endemic goiter and cretinism in Sardinia is known since to ancient time, scanty information collected according to WHO criteria is available. In the present paper the results of an extensive epidemiological survey carried out in juvenile population living in some rural and/or hilly villages in the provinces of Nuoro and Oristano in Central-Southern Sardinia and in urban area of Cagliari, are reported. In the majority of the villages the mean urinary iodine excretion was lower than 60 micrograms/L; the goiter prevalence ranged between 39% and 61% in the district of Nuoro and between 21% and 56% in the district of Oristano. In the control area the urinary iodine excretion was 105 micrograms/L with a goiter prevalence of 12%. Goiter prevalence was not always inversely related to urinary iodine excretion. No relevant thyroid function alterations were found.

IN CONCLUSION

1) in extraurban areas of Central-Southern Sardinia mild to moderate iodine deficiency and endemic goiter are still a widespread problems; 2) also in urban area endemic goiter prevalence is still higher than 10%; 3) extemporary urinary samples are inadequate for assessing the severity of goiter endemia in mild to moderate iodine deficiency; 4) in mildly affected districts palpation is inaccurate for assessing the prevalence of goiter; 5) no relevant alterations of thyroid function were documented in juvenile population.

The disorders induced by iodine deficiency

This paper reviews present knowledge on the etiology, pathophysiology, complications, prevention, and therapy of the disorders induced by iodine deficiency. The recommended dietary allowances of iodine are 100 micrograms/day for adults and adolescents, 60-100 micrograms/day for children aged 1 to 10 years, and 35-40 micrograms/day in infants aged less than 1 year. When the physiological requirements of iodine are not met in a given population, a series of functional and developmental abnormalities occur including thyroid function abnormalities and, when iodine deficiency is severe, endemic goiter and cretinism, endemic mental retardation, decreased fertility rate, increased perinatal death, and infant mortality. These complications, which constitute a hindrance to the development of the affected populations, are grouped under the general heading of iodine deficiency disorders (IDD). At least one billion people are at risk of IDD. Iodine deficiency, therefore, constitutes one of the most common preventable causes of mental deficiency in the world today. Most of the affected populations live in mountainous areas in preindustrialized countries, but 50 to 100 million people are still at risk in Europe. The most important target groups to the effects of iodine deficiency from a public health point of view are pregnant mothers, fetuses, neonates, and young infants because the main complication of IDD, i.e., brain damage resulting in irreversible mental retardation, is the consequence of thyroid failure occurring during pregnancy, fetal, and early postnatal life. The main cause of endemic goiter and cretinism is an insufficient dietary supply of iodine. The additional role of naturally occurring goitrogens has been documented in the case of certain foods (milk, cassava, millet, nuts) and bacterial and chemical water pollutants. The mechanism by which the thyroid gland adapts to an insufficient iodine supply is to increase the trapping of iodide as well as the subsequent steps of the intrathyroidal metabolism of iodine leading to preferential synthesis and secretion of triiodotyronine (T3). They are triggered and maintained by increased secretion of TSH, which is ultimately responsible for the development of goiter. The acceleration of the main steps of iodine kinetics and the degree of hyperstimulation by TSH are much more marked in the pediatric age groups, including neonates, than in adults, and the development of goiter appears as an unfavorable side effect in the process of adaptation to iodine deficiency during growth. The most serious complication of iodine deficiency is endemic cretinism, a syndrome characterized by irreversible mental retardation together with either a predominant neurological syndrome or predominant hypothyroidism, or a combination of both syndromes.(ABSTRACT TRUNCATED AT 400 WORDS)

Early adaptation of thyrotropin and thyroglobulin secretion to experimentally decreased iodine supply in man

Five healthy male volunteers (aged 25 to 28 years) were studied both after 4 weeks of treatment with 200 micrograms iodine/d orally (PO) and following experimental iodine depletion by treatment with 3 x 300 mg perchlorate/d PO over a 4-week period, in an attempt to better define the early adaptive responses to an alteration in iodine supply in thyroid function. Intrathyroidal iodine, serum triiodothyronine (T3), free T3 (FT3), thyroxine (T4), free T4 (FT4), reverse T3 (rT3), thyroxine-binding globulin (TBG), thyroglobulin (Tg), and thyrotropin (TSH) levels (10-minute sampling over 24 hours) were measured at the end of iodine administration and at the end of perchlorate treatment. Thyroid volume was determined by sonography, and iodine content was determined by fluorescence scintigraphy. TSH pulses were analyzed by computer-assisted programs. Comparing both experimental situations, perchlorate treatment significantly reduced intrathyroidal iodine concentration (4.0 +/- 1.3 to 3.0 +/- 1.2 nmol/mL, P less than .05), but thyroid volume and total serum T4, T3, FT3, and TBG levels were not altered. Mean 24-hour serum TSH levels (1.8 +/- 0.3 to 1.0 +/- 0.3 mU/L, P less than .001), amount of TSH secreted/pulse (0.5 +/- 0.1 to 0.3 +/- 0.1 mU/L, P less than .001), and FT4 levels (15.7 +/- 1.7 to 14.3 +/- 1.4 pmol/L, P less than .005) were significantly diminished, whereas Tg levels (18.6 +/- 10.0 to 35.1 +/- 14.0 ng/mL, P less than .01) were significantly increased. Thyroid-specific antibodies were normal and were not altered by treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Study of an endemic goiter area in northern Campania

The purpose of this paper was the determination, in the endemic goiter area of Teano (Caserta, Italy), of: i) The goiter prevalence in a group of 920 patients who attended the Outpatient Endocrinology Department; ii) The urinary iodine excretion in 150 adults (20-73-year-old) and 502 children (10-16-year-old; iii) The thyroid size in the 502 children; iv) The environmental iodine levels. Out of 920 patients a total of 750 (81.5%) goiters were detected. Out of these 750 cases, 415 (55.3%) were of grades 1b and 2, 335 (44.7%) of grades 3 and 4. A statistically significant association between goiter size and age was found (p less than 0.05). Laboratory data were entirely available for 506 goitrous patients. Serum TG levels was increased with goiter size and age, whereas there was a progressive decrease in mean serum TSH levels with increasing goiter size and age. The screening program performed on 502 schoolchildren aged 10 to 16 yr found a 68.3% prevalence of grade 1 goiter and a mean urinary ratio iodine/creatinine of 52 +/- 32 (SD) micrograms/g. A mean urinary ratio iodine/creatinine of 60 +/- 27 (SD) micrograms/g was reported in a sample of 150 adult inhabitants. Iodine measurements in water supplies showed levels equal to or less than 1 microgram/l. The area investigated can be identified as a moderate iodine deficient area and classified as grade 1-2 according to the Pan American Health Organization criteria.

Neuropsychological assessment in schoolchildren from an area of moderate iodine deficiency

Neuropsychological assessment was carried out in schoolchildren from a montane area of Eastern Tuscany (Tiberina Valley). This area was found to be moderately iodine deficient (mean urinary iodine excretion: 39 micrograms/g creatinine), with a cumulative goiter prevalence of 51.9% in schoolchildren aged 6-14 yr (goiter prevalence in the control iodine-sufficient area: 5.6%). No significant differences in serum TT4, TT3, FT4I, TSH levels between the endemic and control areas were found, whereas serum thyroglobulin values were significantly higher in the iodine-deficient area (61 +/- 8 vs 17 +/- 1 ng/ml, p less than 0.01). No differences were found as to the height, body weight and pubertal development in the two areas. Neuropsychological assessment, performed in a representative sample of 50 schoolchildren from the endemic area and 50 schoolchildren from the control area, matched for age, sex and socioeconomical conditions, failed to show major differences between the two groups in the global neuropsychological performance and cognitive levels. However, minor but significant differences were noted in the information vocabulary and coding subtests, at least in children aged 8. Although familial cultural influences might play a role, it would appear that some marginal impairment, with particular regard to motor-perceptual functions, be present in areas of moderate iodine deficiency.

Mild familial goitrous hypothyroidism associated with prolonged 131-iodine retention: possible defect in thyroglobulin synthesis

Four male siblings presented with goitrous hypothyroidism which had been present from the first few years of life. Serum total thyroxine (T4), free T4 index and free T4 levels were low or in the low-normal range while TSH levels were elevated; triiodothyronine (T3) levels were normal. The 131-I-uptake was elevated at 4 and 24 h, 76-93% and 69-82% respectively (normal less than 50%), and remained elevated 96 h after the administration of radioiodine. Administration of potassium perchlorate did not cause a reduction in thyroidal radioiodine. These findings, therefore, were not consistent with defects affecting iodine trapping, iodine organification or iodotyrosine deiodinase. If a coupling defect was the cause of the disorder, iodotyrosines would have to cycle between the thyroid cell and thyroglobulin in the follicular lumen undergoing deiodination, and reorganification continually. To examine this possibility carbimazole, which inhibits organification of iodine was taken orally following administration of 131-I; potassium perchlorate was given to discharge any accumulating nonorganified radioiodine. 131-I uptake changed only from 50 to 48% and from 68 to 71% in the 2 subjects studied. These findings do not support a coupling defect. The possibility of abnormal thyroglobulin synthesis was supported by the finding of inappropriately low serum thyroglobulin levels. A specimen of thyroid tissue demonstrated a 40-fold reduction in normal thyroglobulin content. These findings suggest that our sibship have a rare partial defect in thyroglobulin synthesis and that iodine is incorporated into an alternative complex which is resistant to mobilization.

Low TSH-response to TRH in a former endemic goiter area

During 30 yr of iodine prophylaxis endemic goiter in school children had disappeared in the Savonlinna area which has been the location of continuous surveillance in the East of Finland. In adults goiter is still found to some extent especially in older people. The iodine intake has increased from about 50 to 300 micrograms per day during these yr and the thyroidal uptake of radioactive iodine has decreased from over 60% to between 20 and 30%. However, there is a significant difference in this regard between nongoitrous individuals and goiter patients. In the present study comprising only goiter patients it was found that the thyroidal uptake was significantly higher in the group of patients with a subnormal response to TRH. These patients also had larger goiters and more palpable thyroid nodules than those with a normal response to TRH. The mean age was significantly higher (60.3 yr) as compared to that in the group which had a TSH-response to TRH of greater than 20 mU/l, smaller glands and less thyroid nodules (45.1 yr). The data fit well with the reports on increasing autonomy with increasing age in nontoxic goiter.

Increased serum thyroglobulin concentrations and impaired thyrotropin response to thyrotropin-releasing hormone in euthyroid subjects with endemic goiter in Sicily: their relation to goiter size and nodularity

Serum thyroglobulin (Tg), T4, T3, FT4, FT3, TSH concentrations and TSH response to iv TRH (delta TSH) were measured in 56 consecutive patients with (multi) nodular goiter from a severely iodine-deficient endemic goiter area in Northeastern Sicily and in 11 non goitrous euthyroid individuals living in the same area. Serum Tg concentrations were sharply increased in goitrous subjects (453 +/- 476 ng/ml) and related to thyroid size and the presence of nodules (chi 2 = 43.5, p less than 0.0005). Serum TSH levels measured in goitrous patients (2.1 +/- 0.9 microU/ml) were significantly lower than those measured in nongoitrous iodine deficient subjects (3.1 +/- 0.9 microU/ml, p less than 0.001) and decreased with increasing goiter size and nodularity (chi 2 = 27.3, p less than 0.05). A similar pattern was shown by the analysis of the delta TSH (chi 2 = 43.1, p less than 0.0005). These results suggest that at least a part of the largest and multinodular goiters become autonomously functioning with duration and growing in size. In 13 goitrous patients with absent or impaired response to TRH, a significant direct relation was apparent between log-Tg and goiter size and nodularity (r = 0.64) with an inverse relationship between serum FT3 and delta TSH (r = 0.73). A computed program analysis based on the combination of different independent variables (x) including age, thyroid size and nodularity, serum TSH, log-Tg and FT3, indicated the existence of a significant negative relationship between these variables and the TSH response to TRH (r = 0.75, p = 0).(ABSTRACT TRUNCATED AT 250 WORDS)

Serum free thyroid hormones in subclinical hypothyroidism

Serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations were measured in a group of 52 patients with subclinical hypothyroidism (SH) and in an equal group of age and sex-matched normal controls. SH was defined by normal total T4 (TT4) and total T3 (TT3) concentrations, normal FT4 and FT3 indices, raised TSH levels, in the absence of signs and symptoms of hypothyroidism. Serum FT4 levels averaged 6.1 +/- 1.6 pg/ml (mean +/- SD, p less than 0.001 vs controls), with values below lower normal limits in 33/52 patients; mean FT3 concentrations averaged 3.1 +/- 0.7 pg/ml (p less than 0.001 vs controls), with values below lower normal limits in 8/52 patients. The analysis of results by the Galen and Gambino predictive value model demonstrated a higher sensitivity, but a lower specificity of FT4 as compared to FT3 in the diagnosis of SH. These results indicate that FT4 should be measured in addition to TSH for the diagnosis of impending thyroid failure, thus showing that in many cases patients with so-called subclinical hypothyroidism are actually already mild hypothyroid.

Serum thyrotropin by ultrasensitive immunoradiometric assay and serum free thyroid hormones in pregnancy

Variations of serum TSH, measured by an ultrasensitive immunoradiometric assay, of serum total and free thyroid hormones and of thyroxine-binding globulin (TBG) and sex hormone-binding globulin (SHBG) were investigated in a group of 18 normal women before and during pregnancy. A gradual increase of total thyroid hormones, TBG and SHBG was observed, while mean serum free thyroxine and free triiodothyronine progressively decreased. Serum TSH concentrations were comprised within the normal range throughout pregnancy, although a small but significant increase was found in the 2nd and 3rd trimester. These changes may represent a compensatory mechanism to meet the increased demand for thyroid hormones in pregnancy and must be taken into account for a correct evaluation of thyroid function during gestation.