Serum thyroglobulin as a biomarker of iodine deficiency in adult populations

Thyroid function and urinary concentrations of iodine, selenium, and arsenic in vegans, lacto-ovo vegetarians and pescatarians

PURPOSE

Populations following a plant-based diet may be at particular risk of thyroid dysfunction due to low iodine and selenium intakes. The main purpose was to assess thyroid function and urinary concentration of iodine, selenium, and arsenic, in subjects following a vegan, lacto-ovo vegetarian, or pescatarian diet.

METHODS

In Norway, a country without mandatory dietary iodine fortification, 205 adults, following vegan (n = 115), lacto-ovo vegetarian (n = 55) and pescatarian diet (n = 35) were included. Thyroglobulin (Tg), thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), and serum anti-TPO (S-anti-TPO) were measured in a venous blood sample and concentrations of iodine (UIC), creatinine (UCC), selenium, and arsenic were measured from single spot urine samples.

RESULTS

Subclinical hypothyroidism (TSH > 4.0 mU/L) was observed in 3% of subjects. The overall median (p25, p75) Tg was 17 (9, 30) µg/L and vegans had higher Tg compared to pescatarians. Vegans not consuming iodine-containing supplements (n = 43) had higher Tg, than supplement users (n = 72), 27 (11, 44) vs. 16 (8, 25) µg/L and higher fT4, 16 (15, 17) vs. 15 (14, 17) pmol/L, respectively. The overall median UIC was 57 (28, 130) µg/L, all dietary groups had median UIC below WHO thresholds. Median urinary selenium and arsenic concentration was 13 (6, 22) and 3 (2, 8) µg/L, respectively.

CONCLUSION

The prevalence of subclinical hypothyroidism was low and fT4 and fT3 were within the normal range for all dietary groups. Vegans had significantly increased Tg compared to pescatarians.

Serum thyroglobulin as a biomarker of iodine excess and thyroid disease occurrence in adults

BACKGROUND

Thyroglobulin (Tg) is considered a sensitive indicator of iodine deficiency. However, the usefulness of Tg as a biomarker of excess iodine is uncertain. The present study aimed to determine the influence of different iodine intake on serum Tg levels, evaluate the influence of thyroid diseases on the distribution of Tg, and identify the factors that may affect Tg levels.

METHODS

A cross-sectional survey with a total of 1208 adults was conducted in different water iodine areas in China. Urinary iodine concentration (UIC), water iodine concentration (WIC), serum Tg, thyroid-stimulating hormone (TSH), and thyroid antibodies were measured. The thyroid volumes and nodules were measured by B-scan ultrasound.

RESULTS

Based on the WIC data, subjects were divided into three groups. Based on the median urinary iodine concentration (MUIC) data, the iodine levels were adequate, more than adequate, and excess for the WIC < 10 μg/L group, 10 μg/L ≤ WIC ≤ 100 μg/L g, and WIC > 100 μg/L groups, respectively. The median Tg was significantly higher in the excess iodine group than in the adequate iodine group and the more than adequate iodine group (14.6 μg/L vs.12.7 μg/L, P = 0.042; 14.6 μg/L vs.12.5 μg/L, P = 0.004). Multiple linear regression analysis showed that excess iodine intake, goitre, thyroid nodules, and hypothyroidism were significantly related to higher serum Tg levels.

CONCLUSION

Serum Tg level can be a promising biomarker of excessive iodine intake, but other factors, especially the presence of thyroid disease, should be considered when using this parameter.

A randomized, double-blind study of iodine supplementation during pregnancy in Sweden: pilot evaluation of maternal iodine status and thyroid function

Purpose

Pregnant women in Sweden are mildly iodine deficient. We investigated the effect of daily iodine supplementation on the iodine and thyroid status of pregnant women.

Methods

In this pilot, randomized, double-blind trial, 200 thyroid-healthy pregnant women were recruited at mean (standard deviation) pregnancy week 8.85 (1.62) and assigned (1:1) to daily intake of a multivitamin tablet with or without 150 μg of iodine. Urine and serum samples were collected at baseline and once during the second and third trimesters. Urinary iodine concentration (UIC), serum thyroglobulin (Tg), thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroid peroxidase antibodies (TPOabs) were analyzed. Neonatal TSH data were collected. UIC and Tg were also analyzed in a group of 89 thyroid-healthy non-pregnant women of reproductive age (WRA).

Results

At baseline, the intervention and the control groups had similar median UIC (interquartile range (IQR)): 110 μg/L (74–119) and 111 μg/L (66–168), respectively. The intervention group reached iodine sufficiency with median UIC (IQR) 139 μg/L (89–234) and 136 μg/L (91–211) in the second and third trimester, respectively, without significant difference from the lower limit of the recommended range, i.e. 150–250 μg/L (p = 0.42 and p = 0.87, respectively). The intervention group had higher median UIC and lower median Tg compared to the control group during the second (p < 0.001 and p = 0.019, respectively) and third trimester (p < 0.001 and p = 0.003, respectively), whereas thyroid hormones, serum TPOabs, and neonatal TSH were similar. The WRA group presented median UIC (IQR) 65 μg/L (30–98) and median Tg (IQR) 18 μg/L (13–27).

Conclusion

A daily supplement containing 150 μg of iodine to a group of pregnant women with mild iodine deficiency improved the iodine status from mild ID to iodine sufficiency. This improvement seems to have had a positive impact on maternal thyroglobulin. This study is now under extension to investigate the children’s neuropsychological development.

Trial registration

ClinicalTrials.gov Identifier NCT02378246, May 3, 2015, retrospectively registered.

Early detection of progressive disease using thyroglobulin doubling-time in metastatic differentiated thyroid carcinoma treated with radioactive iodine

OBJECTIVE

Detectable serum thyroglobulin (Tg) in patients with differentiated thyroid carcinoma (DTC) after total thyroidectomy indicates progression of the disease. Thyroglobulin doubling-time (TgDT) is a powerful prognostic predictor in patients with DTC. We aimed to evaluate the value of the dynamic TgDT for early detection of progressive disease (PD) in the patients of metastatic DTC with I radioactive iodine (RAI) therapy.

METHODS

We retrospectively evaluated 21 patients undergoing RAI therapy with metastatic DTC. Patients were defined as PD or non-PD according to Response Evaluation Criteria in Solid Tumors 1.1. TgDT was calculated by Excel-based software using Tg values measured during routine follow-up. Whole data (WDT), initial four data (IDT) and recent four data (RDT) of TgDT after total thyroidectomy were calculated and compared.

RESULTS

Among the 21 patients (10 men; median age, 62 years old; range, 33-80), 11 patients were classified into PD and 10 were into non-PD. The initial Tg after total thyroidectomy showed a significant difference between PD and non-PD patients (P = 0.013). Short WDT, IDT and RDT (less than one year) showed a high correlation with PD (P < 0.05). RDT showed the highest predictive value for PD (P < 0.001). All the 11 PD patients showed RDT less than one year before PD (median follow-up, 157 days; range, 88-252).

CONCLUSIONS

RDT is a powerful PD predictor in patients with metastatic DTC. Dynamic monitoring of RDT should be applied for the early detection of PD in clinic.

Association between iodine intake and thyroid autoantibodies: a cross-sectional study of 7073 early pregnant women in an iodine-adequate region

PURPOSE

The association between iodine intake and thyroid autoimmunity has been debated, especially in pregnant women. This study aimed to investigate thyroid autoantibodies and their association with iodine intake and hypothyroidism in early pregnancy.

METHODS

7073 early pregnant women from an iodine-sufficient region participated in this study. Urinary iodine concentrations (UICs) were measured using an ammonium persulfate method. Serum thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), thyroid-stimulating hormone (TSH), free thyroxine (FT4), and Tg were determined using an electrochemiluminescence immunoassay.

RESULTS

Iodine deficiency (UIC < 100 μg/L) was associated with higher risks of TPOAb positivity [adjusted odds ratio (aOR) = 1.64, 95% confidence interval [CI] (1.29-2.08)] and TgAb positivity [aOR = 1.44, 95% CI (1.16-1.80)]. Women with isolated TPOAb positivity, isolated TgAb positivity, or both TPOAb and TgAb positivity had a 14.64-fold, 7.83-fold, and 44.69-fold increased risk of overt hypothyroidism, and a 4.36-fold, 2.86-fold, and 6.26-fold increased risk of subclinical hypothyroidism, respectively. Moreover, the risks of overt and subclinical hypothyroidism in women with a high TPOAb titer were 16.99 and 4.80 times that in TPOAb-negative women, respectively. The risk of overt hypothyroidism in women with a high TgAb titer was 6.97 times that in TgAb-negative women.

CONCLUSIONS

Our work demonstrates that iodine deficiency during early pregnancy is an independent risk factor for both TPOAb positivity and TgAb positivity. Furthermore, positivity for both autoantibodies and a high thyroid autoantibody titer are associated with significantly higher risks of overt and subclinical hypothyroidism.

Excess iodine intake: sources, assessment, and effects on thyroid function

Iodine is essential for thyroid hormone synthesis. High iodine intakes are well tolerated by most healthy individuals, but in some people, excess iodine intakes may precipitate hyperthyroidism, hypothyroidism, goiter, and/or thyroid autoimmunity. Individuals with preexisting thyroid disease or those previously exposed to iodine deficiency may be more susceptible to thyroid disorders due to an increase in iodine intake, in some cases at intakes only slightly above physiological needs. Thyroid dysfunction due to excess iodine intake is usually mild and transient, but iodine-induced hyperthyroidism can be life-threatening in some individuals. At the population level, excess iodine intakes may arise from consumption of overiodized salt, drinking water, animal milk rich in iodine, certain seaweeds, iodine-containing dietary supplements, and from a combination of these sources. The median urinary iodine concentration (UIC) of a population reflects the total iodine intake from all sources and can accurately identify populations with excessive iodine intakes. Our review describes the association between excess iodine intake and thyroid function. We outline potential sources of excess iodine intake and the physiological responses and consequences of excess iodine intakes. We provide guidance on choice of biomarkers to assess iodine intake, with an emphasis on the UIC and thyroglobulin.

Thyroglobulin Is Markedly Elevated in 6- to 24-Month-Old Infants at Both Low and High Iodine Intakes and Suggests a Narrow Optimal Iodine Intake Range

BACKGROUND

In areas with incomplete salt iodization coverage, infants and children aged 6-24 months weaning from breast milk and receiving complementary foods are at risk of iodine deficiency. However, few data exist on the risk of excessive iodine intake in this age group. Thyroglobulin (Tg) is a sensitive marker of iodine intake in school-age children and adults and may be used to estimate the optimal iodine intake range in infancy. The aim of this study was to assess the association of low and high iodine intakes with Tg and thyroid function in weaning infants.

METHODS

This multicenter cross-sectional study recruited infants aged 6-24 months (n = 1543; M_age = 12.2 ± 4.6 months) receiving breast milk with complementary foods, from seven countries in areas with previously documented deficient, sufficient, or excessive iodine intake in schoolchildren or pregnant women. Urinary iodine concentration (UIC) and Tg, total thyroxine, and thyrotropin were measured using dried blood spot testing.

RESULTS

Median UIC ranged from 48 μg/L (interquartile range 31-79 μg/L) to 552 μg/L (interquartile range 272-987 μg/L) across the study sites. Median Tg using dried blood spot testing was high (>50 μg/L) at estimated habitual iodine intakes <50 μg/day and >230 μg/day. Prevalence of overt thyroid disorders was low (<3%). Yet, subclinical hyperthyroidism was observed in the countries with the lowest iodine intake.

CONCLUSIONS

Tg is a sensitive biomarker of iodine intake in 6- to 24-month-old infants and follows a U-shaped relationship with iodine intake, suggesting a relatively narrow optimal intake range. Infants with low iodine intake may be at increased risk of subclinical thyroid dysfunction. In population monitoring of iodine deficiency or excess, assessment of iodine status using UIC and Tg may be valuable in this young age group.

Effect of Excess Iodine Intake from Iodized Salt and/or Groundwater Iodine on Thyroid Function in Nonpregnant and Pregnant Women, Infants, and Children: A Multicenter Study in East Africa

BACKGROUND

Acute excess iodine intake can damage the thyroid, but the effects of chronic excess iodine intake are uncertain. Few data exist for pregnant and lactating women and infants exposed to excessive iodine intake.

METHODS

This was a multicenter cross-sectional study. At study sites in rural Kenya and urban Tanzania previously reporting iodine excess in children, urinary iodine concentration (UIC), thyrotropin, total thyroxine, and thyroglobulin (Tg) were measured in school-age children (SAC), women of reproductive age, pregnant (PW) and lactating women, and breast-feeding and weaning infants. In a national study in Djibouti, UIC was measured in SAC and PW. At all sites, daily iodine intake was estimated based on UIC, and iodine concentration was measured in household salt and drinking water.

RESULTS

The total sample size was 4636: 1390, 2048, and 1198 subjects from Kenya, Tanzania, and Djibouti, respectively. In Kenya and Tanzania: (i) median UIC was well above thresholds for adequate iodine nutrition in all groups and exceeded the threshold for excess iodine intake in SAC; (ii) iodine concentrations >40 mg of iodine/kg were found in approximately 55% of household salt samples; (iii) iodine concentrations ≥10 μg/L were detected in 9% of drinking water samples; (iv) Tg was elevated in all population groups, but the prevalence of thyroid disorders was negligible, except that 5-12% of women of reproductive age had subclinical hyperthyroidism and 10-15% of PW were hypothyroxinemic. In Djibouti: (i) the median UIC was 335 μg/L (interquartile range [IQR] = 216-493 μg/L) in SAC and 265 μg/L (IQR = 168-449 μg/L) in PW; (ii) only 1.6% of Djibouti salt samples (n = 1200) were adequately iodized (>15 mg/kg); (iii) the median iodine concentration in drinking water was 92 μg/L (IQR = 37-158 μg/L; n = 77). In all countries, UIC was not significantly correlated with salt or water iodine concentrations.

CONCLUSIONS

Although iodine intake was excessive and Tg concentrations were elevated, there was little impact on thyroid function. Chronic excess iodine intake thus appears to be well tolerated by women, infants, and children. However, such high iodine intake is unnecessary and should be avoided. Careful evaluation of contributions from both iodized salt and groundwater iodine is recommended before any review of iodization policy is considered.

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.

Reliability of thyroglobulin in serum compared with urinary iodine when assessing individual and population iodine nutrition status

The occurrence of thyroid disorders relies on I nutrition and monitoring of all populations is recommended. Measuring I in urine is standard but thyroglobulin in serum is an alternative. This led us to assess the reliability of studies using serum thyroglobulin compared with urinary I to assess the I nutrition level and calculate the number of participants needed in a study with repeated data sampling in the same individuals for 1 year. Diet, supplement use and life style factors were assessed by questionnaires. We measured thyroglobulin and thyroglobulin antibodies in serum and I in urine. Participants were thirty-three Caucasians and sixty-four Inuit living in Greenland aged 30–49 years. Serum thyroglobulin decreased with rising I excretion (Kendall’sτ−0·29,P=0·005) and did not differ with ethnicity. Variation in individuals was lower for serum-thyroglobulin than for urinary I (mean individual CV: 15·1v. 46·1 %;P<0·01). It required 245 urine samples to be 95 % certain of having a urinary I excretion within 10 % of the true mean of the population. For serum-thyroglobulin the same precision required 206 samples. In an individual ten times more samples were needed to depict I deficiency when using urinary I excretion compared with serum-thyroglobulin. In conclusion, more participants are need to portray I deficiency in a population when using urinary I compared with serum-thyroglobulin, and about ten times more samples are needed in an individual. Adding serum-thyroglobulin to urinary I may inform surveys of I nutrition by allowing subgroup analysis with similar reliability.

Gestation-specific changes in maternal thyroglobulin during pregnancy and lactation in an iodine-sufficient region in China: a longitudinal study

OBJECTIVES

To describe the changes in thyroglobulin (Tg) based upon gestational and postpartum concentrations in healthy pregnant women from an iodine-sufficient region in China, and to evaluate the use of Tg as a biomarker for iodine-sufficient pregnant women.

DESIGN

A longitudinal study of Tg change in normal pregnant women from an iodine-sufficient region.

PATIENTS AND MEASUREMENTS

Blood and urine samples were obtained from 133 pregnant women. Urinary iodine concentration (UIC) was measured using an ammonium persulfate method. Serum iodine concentration was required by inductively coupled plasma mass spectrometry (ICP-MS). Serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), total thyroxine (TT4), total triiodothyronine (TT3), antithyroid peroxidase antibody (TPOAb), antithyroglobulin antibody (TgAb) and Tg were measured using an electrochemiluminescence immunoassay.

RESULTS

Thyroglobulin concentrations were higher in early pregnancy (pregnancy at 8 weeks vs nonpregnancy: 11·42 ng/ml vs 8·8 ng/ml, P < 0·01) and maintained a stable level, and then increased greatly at the 36th week. After delivery, Tg decreased to nonpregnant levels. During pregnancy, maternal Tg was not correlated with thyroid function, UIC or urine iodine-creatinine ratio (UI/Cr). Cord blood Tg was much higher compared to maternal Tg levels at the 36w (57·34 vs 14·86 ng/ml, P < 0·001) and correlated positively with cord FT4 (r = 0·256, P < 0·05), cord TT4 (r = 0·263, P < 0·05) and maternal UI/Cr at 36w (r = -0·214, P < 0·05).

CONCLUSIONS

Our work demonstrates that Tg is elevated during pregnancy, and the effect of pregnancy should be taken into consideration when Tg is used as a biomarker for the iodine status. Cord blood Tg is much higher than maternal Tg levels at the 36w and is correlated with maternal iodine status.