Reference range of thyroid hormones in normal Indian school-age children

The association between per-/polyfluoroalkyl substances in serum and thyroid function parameters: A cross-sectional study on teenagers living near a Chinese fluorochemical industrial plant

Thyroid hormones (THs) play an important role in a wide range of crucial biological functions related to growth and development, and thyroid antibodies (TAs) can influence the biosynthesis of THs. Epidemiological studies have indicated that per- and polyfluoroalkyl substances (PFAS) could induce thyroid disruption, but studies on teenagers living in areas with high PFAS exposure are limited. This cross-sectional study focused on 836 teenagers (11- 15 years) living near a Chinese fluorochemical industrial plant. Decreased levels of free thyroxine (FT4, ﹤9.6 pmol/L, abnormal rate = 19.0 %) and elevated levels of free triiodothyronine (FT3, ﹥6.15 pmol/L, abnormal rate = 29.8 %) were observed. Correlations of serum PFAS concentrations and TAs/THs were analyzed. Increased PFOA was identified as a risk factor of decreased FT4 by using unadjusted (OR: 11.346; 95 % CI: 6.029, 21.352, p < 0.001) and adjusted (OR: 12.566; 95 % CI: 6.549, 24.115, p < 0.001) logistic regression models. In addition, significantly negative correlations were found between log10 transformed PFOA and FT4 levels using linear (unadjusted: β = -1.543, 95 % CI: -1.937, -1.148, p < 0.001; adjusted: β = -1.534, 95 % CI: -1.930, -1.137, p < 0.001) and BKMR models. For abnormal FT3, a significantly positive association between PFHxS and FT3 levels was observed in a regression model (unadjusted: β = -0.903, 95 % CI: -1.212, -0.595, p < 0.001; adjusted: β = -0.894, 95 % CI: -1.204, -0.583, p < 0.001), and PFHxS was identified as a risk factor (unadjusted: OR: 4.387; 95 % CI: 2.619, 7.346, p < 0.001; adjusted: OR: 4.527; 95 % CI: 2.665, 7.688, p < 0.001). Sensitivity analyses confirmed the robustness of the above results. This study reported the elevated PFAS exposure and thyroid function of teenagers living near a fluorochemical industrial plant from China.

Age-related variation in thyroid function - a narrative review highlighting important implications for research and clinical practice

BACKGROUND

Thyroid hormones are key determinants of health and well-being. Normal thyroid function is defined according to the standard 95% confidence interval of the disease-free population. Such standard laboratory reference intervals are widely applied in research and clinical practice, irrespective of age. However, thyroid hormones vary with age and current reference intervals may not be appropriate across all age groups. In this review, we summarize the recent literature on age-related variation in thyroid function and discuss important implications of such variation for research and clinical practice.

MAIN TEXT

There is now substantial evidence that normal thyroid status changes with age throughout the course of life. Thyroid stimulating hormone (TSH) concentrations are higher at the extremes of life and show a U-shaped longitudinal trend in iodine sufficient Caucasian populations. Free triiodothyronine (FT3) levels fall with age and appear to play a role in pubertal development, during which it shows a strong relationship with fat mass. Furthermore, the aging process exerts differential effects on the health consequences of thyroid hormone variations. Older individuals with declining thyroid function appear to have survival advantages compared to individuals with normal or high-normal thyroid function. In contrast younger or middle-aged individuals with low-normal thyroid function suffer an increased risk of adverse cardiovascular and metabolic outcomes while those with high-normal function have adverse bone outcomes including osteoporosis and fractures.

CONCLUSION

Thyroid hormone reference intervals have differential effects across age groups. Current reference ranges could potentially lead to inappropriate treatment in older individuals but on the other hand could result in missed opportunities for risk factor modification in the younger and middle-aged groups. Further studies are now needed to determine the validity of age-appropriate reference intervals and to understand the impact of thyroid hormone variations in younger individuals.

Possible Association Between Thyroid Nodule Formation and Developmental Alterations in the Pituitary-Thyroid Hormone Axis in Children and Adolescents: The Fukushima Health Management Survey

Background: We previously found low thyrotropin (TSH) levels in children and adolescents with thyroid nodules, including papillary thyroid cancer, although it is generally accepted that high TSH levels are a risk factor for formation and growth of thyroid nodules in adults. To clarify the reasons for the discrepancy, we precisely analyzed the features of pituitary-thyroid hormone (TH) actions in children and adolescents with or without nodules at different ages. Methods: Among the 4955 participants who participated in a second screening by thyroid ultrasound examination in the Fukushima Health Management Survey, 721 and 2849 euthyroid participants aged 6-20 years without or with nodules, including thyroid cancer, were selected for evaluation of TH regulation. The responsivity of TSH to THs was assessed by two thyroid feedback quantile-based indices (T4FQI and T3FQI). Logistic regression analyses were conducted to calculate the odds ratios (ORs) of serum concentrations related to thyroid functions for positive thyroid nodules compared with negative nodules. Results: The feedback indices declined in a sex-specific manner with aging. In particular, T3FQI, the index for TSH response to free triiodothyronine (fT3), started to decline after ∼10 and 15 years of age in female and male participants, respectively. Compared with the absence of nodules, the age- and sex-adjusted ORs (confidence intervals) for logTSH, free thyroxine (fT4), fT3, T4FQI, T3FQI, and thyroglobulin levels were 0.586 (0.501-0.685), 1.036 (0.595-1.805), 1.059 (0.842-1.332), 0.569 (0.454-0.715), 0.564 (0.443-0.719), and 1.01 (1.005-1.014), respectively. Associations between the presence of nodules and either low logTSH or low feedback indices were observed in participants aged between 12 and 17 years among the total cohort. Conclusions: The relationships between the levels of TSH and THs changed in a sex-dependent manner in children and adolescents. The age-dependent shift in the pituitary-TH set point may be associated with age-dependent nodule formation during restricted periods of growth and maturation in both young female and male participants.

Thyroid Function Changes and Pubertal Progress in Females: A Longitudinal Study in Iodine-Sufficient Areas of East China

BACKGROUND

The onset of puberty is influenced by thyroid function, and thyroid hormones (THs) fluctuate substantially during the period of pubertal development. However, it needs to be further clarified how THs change at specific puberty stages and how it influences pubertal development in girls. So far, longitudinal data from China are scarce.

METHODS

A cohort study was conducted among girls during puberty in iodine-sufficient regions of East China between 2017 to 2019. Serum thyroid stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were determined for each participant. Thyroid homeostasis structure parameters (THSPs), including the ratio of FT4 to FT3 (FT4/FT3), Jostel's TSH index (TSHI), and thyroid feedback quantile-based index (TFQI), were calculated. Puberty category scores (PCS), calculated based on the Puberty Development Scale (PDS), was used to assess the stage of puberty. Girls were grouped into three categories according to PCS changes (△PCS) and six categories according puberty stage (B_PF_P: pre-pubertal at both baseline and follow-up; B_PF_L: pre-pubertal at baseline and late-pubertal at follow-up, respectively; B_PF_T: pre-pubertal at baseline and post-pubertal at follow-up, respectively; B_LF_L: late-pubertal at both baseline and follow-up; B_LF_T: late-pubertal at baseline and post-pubertal at follow-up, respectively; B_TF_T: post-pubertal at both baseline and follow-up). Multiple linear regression analyses were used to evaluate the associations of THs changes with pubertal progress.

RESULTS

The levels of serum TSH and FT3 decreased while serum FT4 increased during the study period (P<0.001). In multiple linear regression analyses, after adjustment for covariables, FT3 decreased by an additional 0.24 pmol/L (95% CI: -0.47 to -0.01) in the higher △PCS group than the lower △PCS group. Compared with the B_LF_L group, the B_PF_T group showed an additional decline in FT3 (β= -0.39 pmol/L, 95%CI: -0.73 to -0.04), the B_TF_T group showed a lower decline in TSH (β=0.50 mU/L, 95% CI: 0.21 to 0.80) and a lower decline in TSHI (β=0.24, 95%CI: 0.06 to 0.41), respectively. There was no association of △FT4 or △TFQI with △PCS or the puberty pattern.

CONCLUSIONS

Serum TSH and FT3 decreased while serum FT4 increased among girls during puberty. Both the initial stage and the velocity of pubertal development were related to thyroid hormone fluctuations.

Evaluation of uric acid levels, thyroid function, and anthropometric parameters in Japanese children with Down syndrome

Down syndrome, caused by trisomy 21, is characterized by congenital abnormalities as well as mental retardation. From the neonatal stage through adolescence, patients with Down syndrome often have several complications. Thus, it is important to attain knowledge of the prevalence of these comorbidities in children with Down syndrome. We, therefore, evaluated the biochemical data, thyroid function, and anthropometric parameters, and analyzed the association among them in Japanese children and early adolescents with Down syndrome. There was no difference in the prevalence of obesity and overweight between boys and girls. The level of uric acid was higher in boys than in girls. Moreover, the prevalence of hyperuricemia was also higher in boys than in girls (approximately 32% and 10%, respectively). The prevalence of subclinical hypothyroidism in children with Down syndrome was approximately 20%, with no significant sex differences. The levels of uric acid and dehydroepiandrosterone-sulfate were positively associated with age, while the levels of thyroid-stimulating hormone and free thyroxine had a negative association with age. Overall, children with Down syndrome, exhibit a higher incidence of hyperuricemia. Therefore, uric acid levels, as well as thyroid function, from childhood to early adulthood should be monitored in this patient cohort.

Thyroid profile and autoantibodies in Type 1 diabetes subjects: A perspective from Eastern India

CONTEXT

There has been a rise in the incidence of type 1 diabetes mellitus (T1DM) in India. The prevalence of thyroid autoantibodies and thyroid dysfunction is common in T1DM.

AIMS

The aim of this study is to determine the incidence of thyroid dysfunction and thyroid autoantibodies in T1DM subjects, without any history of thyroid disease, and the prevalence of glutamic acid decarboxylase (GAD) antibody, Islet antigen-2 antibody (IA2), thyroid peroxidase (TPO), and thyroglobulin autoantibodies (Tg-AB) in T1DM subjects.

SETTINGS AND DESIGN

This was a cross-sectional clinical-based study.

SUBJECTS AND METHODS

Fifty subjects (29 males, 31 females) with T1DM and without any history of thyroid dysfunction were included in the study. All subjects were tested for GAD antibody, IA2 antibody, TPO antibody, thyroglobulin antibody, free thyroxine, and thyroid-stimulating hormone.

STATISTICAL ANALYSIS USED

A Chi-square/pooled Chi-square test was used to assess the trends in the prevalence of hypothyroidism. A two-tailed P < 0.05 was considered statistically significant.

RESULTS

The mean age of the subjects was 23.50 years. 9.8% of subjects were below the age of 12 years, 27.45% of subjects were of age 12-18 years, 37.25% of subjects were of age 19-30 years, and 25.49% of subjects were above 30 years. 78% were positive autoantibody for GAD, 30% for IA-2, 24% for TPO, and 16% were positive for Tg-AB. A total of 6.0% of T1DM subjects had evidence of clinical hypothyroidism, but the prevalence of subclinical hyperthyroidism (SCH) varied from 32% to 68.0% for we considered different definitions of SCH as advocated by different guidelines. All subjects with overt hypothyroidism had positive GAD and thyroid autoantibodies. One (2%) subject had clinical hyperthyroidism with strongly positive GAD, TPO, and Tg-AB.

CONCLUSIONS

We found a high prevalence of GAD, IA2, TPO, and Tg-AB in our T1DM subjects. A substantial proportion of our subjects had undiagnosed thyroid dysfunction with a preponderance of subclinical hypothyroidism. All T1DM subjects with overt hypothyroidism or hyperthyroidism had positive GAD and thyroid autoantibodies. The high prevalence of undiagnosed thyroid dysfunction highlights the importance of regular thyroid screening in T1DM subjects.

TSH enhancement of FT4 to FT3 conversion is age dependent

OBJECTIVE

We previously reported increasing free T3 (FT3) to free T4 (FT4) ratios as thyroid-stimulating hormone (TSH) increases within the normal range in children. It is not known if this phenomenon is age-related among humans, as previously reported in rats. This study examines the relationships between TSH and FT3/FT4 ratios in different ages.

DESIGN

Retrospective examination of thyroid tests from patients without thyroid disease from community clinics.

METHODS

Free T3, free T4, and TSH levels from 527 564 sera collected from patients aged 1 year or greater were studied. Exclusion criteria were the following: missing data, TSH greater than 7.5mIU/L, and medications that may interfere with thyroid hormone activity. A total of 27 940 samples remaining after exclusion were stratified by age. Samples with available anthropometric data were additionally stratified for body mass index (BMI). Correlations of TSH to FT4, FT3, and FT3/FT4 ratios by age group were examined.

RESULTS

Up to age 40, for each increasing TSH quartile, FT3 and the FT3/FT4 ratio increased and FT4 decreased significantly (for both FT3, FT4 and FT3/FT4 ratio, P<0.05 for every TSH quartile when compared with the 1st quartile, except FT3 in the 30-40 age group). In older age groups, increasing TSH was not associated with increased FT3/FT4 ratio.

CONCLUSION

As TSH levels increase, FT3/FT4 ratios increase until age 40, but this differential increase does not occur in older age groups. This may reflect a decrease in thyroxine (T4) to triiodothyronine (T3) conversion with age, which may be part of the aging process.

Subclinical hypothyroidism in children

NEED AND PURPOSE OF REVIEW

Subclinical hypothyroidism is a biochemical diagnosis characterized by raised thyroid stimulating hormone and normal free T4, without clinical features of hypothyroidism. This review analyzes the current evidence to arrive at a consensus and algorithm to manage this condition.

METHODS

We searched Pubmed, Cochrane and Embase for articles published between 1990 to 2014, and identified 13 relevant articles dealing with pediatric subclinical hypothyroidism which were suitable to include in our review.

CONCLUSIONS

Subclinical hypothyroidism is often a benign problem which requires expectant management with periodic monitoring of thyroid function tests and natural progression to overt hypothyroidism occur lot less frequently than expected. There is a paucity of robust randomized intervention studies, especially studies focusing on clinical outcomes. Thyroid replacement therapy is not justified in children with subclinical hypothyroidism when Thyroid stimulating hormone is <10 mIU/L. The main risk factors for progression to overt hypothyroidism are female sex, goiter, family history of thyroid disorder, strongly positive thyroid peroxidase antibodies and symptoms suggesting hypothyroidism. An algorithm for managing this condition is suggested.

Assessment of iodine nutrition in pregnant north Indian subjects in three trimesters

OBJECTIVE

The cross-sectional study was carried out to assess the iodine status of pregnant women, using median urinary iodine concentration (MUI) as the measure of outcome, to document the impact of advancing gestation on the MUI in normal pregnancy.

MATERIALS AND METHODS

The present study assessed the MUI in casual urine samples from 50 pregnant subjects of each trimester and 50 age-matched non-pregnant controls.

RESULTS

The median (range) of urinary iodine concentration (UIC) in pregnant women was 304 (102-859) μg/L and only 2% of the subjects had prevalence of values under 150 μg/L (iodine insufficiency). With regard to the study cohort, median (range) UIC in the first, second, and third trimesters was 285 (102-457), 318 (102-805), and 304 (172-859) μg/L, respectively. Differences between the first, second, and third trimesters were not statistically significant. The MUI in the controls (305 μg/L) was not statistically different from the study cohort.

CONCLUSION

The pregnant women had no iodine deficiency, rather had high median urinary iodine concentrations indicating more than adequate iodine intake. Larger community-based studies are required in iodine-sufficient populations, to establish gestation-appropriate reference ranges for UIC in pregnancy.

The evolution of thyroid function with puberty

OBJECTIVE

This study was planned to describe thyroid functional status in different stages of puberty.

STUDY DESIGN

We collected data from five schools across different geographical zones of Delhi. All children who consented were evaluated for anthropometry, pubertal stage, goitre status, serum free T3 (FT3), free T4 (FT4), TSH, anti-TPO (thyroid peroxidase) antibodies and thyroid ultrasound. From this sample, a disease- and risk-free or 'reference population' was obtained by excluding those with history of thyroid disease or use of thyroid medications, family history of thyroid disease, goitre, hypoechogenicity or nodularity on ultrasound or positive antithyroid antibodies.

RESULTS

The 'total population' comprised 3722 children; the 'reference population' comprised 2134 subjects. The mean, median, 3rd and 97th percentiles of serum FT3, FT4 and TSH for each stage of puberty were obtained. In both boys and girls, FT3 increased with entry into puberty and either stayed constant or declined marginally after stage 3 of puberty. In contrast, in both genders, FT4 decreased with entry into puberty and stayed relatively constant after stage 3 of puberty. TSH levels declined through puberty in boys, but remained largely unchanged in girls. An increased conversion of T4 to T3 is the possible explanation for this finding.

CONCLUSIONS

This large community-based study in school-age children using strict exclusion criteria provides data of thyroid function in the various stages of puberty. There is no evidence of 'thyroidarche' during or preceding puberty.

Thyroid disorders in India: An epidemiological perspective

Thyroid diseases are common worldwide. In India too, there is a significant burden of thyroid diseases. According to a projection from various studies on thyroid disease, it has been estimated that about 42 million people in India suffer from thyroid diseases. This review will focus on the epidemiology of five common thyroid diseases in India: (1) hypothyroidism, (2) hyperthyroidism, (3) goiter and iodine deficiency disorders, (4) Hashimoto's thyroiditis, and (5) thyroid cancer. This review will also briefly cover the exciting work that is in progress to ascertain the normal reference range of thyroid hormones in India, especially in pregnancy and children.

Obesity and thyrotropinemia

OBJECTIVE

To study the relation between body mass index (BMI) and TSH in euthyroid and subclinical hypothyroid obese children and compared serum TSH level among obese and overweight children.

METHODS

Fifty consecutive children (aged 2-18 yr) presenting for obesity were studied. All cases with TSH > 10, low T3/T4, organic and syndromic obesity were excluded. Patients were divided into Group 1: Overweight (n=20) (BMI between 85(th) to 95(th) centile) and Group 2: Obesity (n=30) (BMI > 95(th) centile). Fisher's exact test, Mann-Whitney U test and Pearson's correlation were used for statistical analysis. P value < 0.05 was considered significant.

RESULTS

Elevated TSH level (between 4.5-10 mIU/L) with normal T3, T4 was seen in 4/20 overweight and 9/30 of obese children (P=0.5219). The mean TSH was comparable in both the groups (3.22 +/- 3.1 mIU/L vs. 3.63 +/- 2.2 mIU/L, P=0.3491). Overall TSH showed no correlation with BMI (r= 0.0014, P=0.9924).

CONCLUSION

The preliminary data did not show any relation between severity of obesity and TSH level. Further large scale data from population are required to confirm these findings.

Subclinical hypothyroidism after radioiodine exposure: Ukrainian-American cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident (1998-2000)

BACKGROUND

Hypothyroidism is the most common thyroid abnormality in patients treated with high doses of iodine-131 (131I). Data on risk of hypothyroidism from low to moderate 131I thyroid doses are limited and inconsistent.

OBJECTIVE

This study was conducted to quantify the risk of hypothyroidism prevalence in relation to 131I doses received because of the Chornobyl accident.

METHODS

This is a cross-sectional (1998-2000) screening study of thyroid diseases in a cohort of 11,853 individuals < 18 years of age at the time of the accident, with individual thyroid radioactivity measurements taken within 2 months of the accident. We measured thyroid-stimulating hormone (TSH), free thyroxine, and antibodies to thyroid peroxidase (ATPO) in serum.

RESULTS

Mean age at examination of the analysis cohort was 21.6 years (range, 12.2-32.5 years), with 49% females. Mean 131I thyroid dose was 0.79 Gy (range, 0-40.7 Gy). There were 719 cases with hypothyroidism (TSH > 4 mIU/L), including 14 with overt hypothyroidism. We found a significant, small association between (131)I thyroid doses and prevalent hypothyroidism, with the excess odds ratio (EOR) per gray of 0.10 (95% confidence interval, 0.03-0.21). EOR per gray was higher in individuals with ATPO < or = 60 U/mL compared with individuals with ATPO > 60 U/mL (p < 0.001).

CONCLUSIONS

This is the first study to find a significant relationship between prevalence of hypothyroidism and individual (131)I thyroid doses due to environmental exposure. The radiation increase in hypothyroidism was small (10% per Gy) and limited largely to subclinical hypothyroidism. Prospective data are needed to evaluate the dynamics of radiation-related hypothyroidism and clarify the role of antithyroid antibodies.