Reference interval for thyrotropin in a ultrasonography screened Korean population

Management of Subclinical Hypothyroidism: A Focus on Proven Health Effects in the 2023 Korean Thyroid Association Guidelines

Subclinical hypothyroidism (SCH) is characterized by elevated thyroid-stimulating hormone (TSH) and normal free thyroxine levels. The Korean Thyroid Association recently issued a guideline for managing SCH, which emphasizes Korean-specific TSH diagnostic criteria and highlights the health benefits of levothyroxine (LT4) treatment. A serum TSH level of 6.8 mIU/L is presented as the reference value for diagnosing SCH. SCH can be classified as mild (TSH 6.8 to 10.0 mIU/L) or severe (TSH >10.0 mIU/L), and patients can be categorized as adults (age <70 years) or elderly (age ≥70 years), depending on the health effects of LT4 treatment. An initial increase in serum TSH levels should be reassessed with a subsequent measurement, including a thyroid peroxidase antibody test, preferably 2 to 3 months after the initial assessment. While LT4 treatment is not generally recommended for mild SCH in adults, it is necessary for severe SCH in patients with underlying coronary artery disease or heart failure and it may be considered for those with concurrent dyslipidemia. Conversely, LT4 treatment is generally not recommended for elderly patients, regardless of SCH severity. For those SCH patients who are prescribed LT4 treatment, the dosage should be personalized, and serum TSH levels should be regularly monitored to maintain the optimal LT4 regimen.

A New Method for Early Screening of Gastric Cancer (G17 and CA724 Dual-Labeled Time-Resolved Fluorescence Immunoassay)

Gastric carcinoma (GC) is one of the most common malignancies in the world with the great early screening challenges. The study is aimed at establishing a new detection method for early screening GC using time-resolved fluorescence immunoassay (TRFIA) via quantitative detection of gastrin-17 (G-17) and carbohydrate antigen 724 (CA724) in serum. Time-resolved analyzer measured the fluorescence intensity. The standards of G-17/CA724 were used for drawing the standard curve, which is used to calculate the concentration of G-17 and CA724 in serum sample. The sensitivity for G-17 was 0.54 pg/mL and for CA724 was 0.28 U/mL with a wide-range analyze concentration (0.1-1000) pg/mL or U/mL. The average recoveries ranged from 100.52% to 110.30% for G-17 and 103.02% to 116.00% for CA724. All CVs of the intra- and interassay were below 10% with high specificity. There was a high Pearson coefficient between this TRFIA method and the commercially available kits (Pearson r 0.9117 for G-17 and 0.9449 for CA724). Additionally, the cutoff value was 88.41 pg/mL and 5.47 U/mL for CA724 in health subjects. This study established a TRFIA method for simultaneous detection of the concentrations of G-17 and CA724 in serum, which provide a new method for sensitive, accurate, and specific early screening of gastric cancer.

Sex Bias in Differentiated Thyroid Cancer

Differentiated thyroid cancers are more frequent in women than in men. These different frequencies may depend on differences in patient's behavior and in thyroid investigations. However, an impact on sexual hormones is likely, although this has been insufficiently elucidated. Estrogens may increase the production of mutagenic molecules in the thyroid cell and favor the proliferation and invasion of tumoral cells by regulating both the thyrocyte enzymatic machinery and the inflammatory process associated with tumor growth. On the other hand, the worse prognosis of thyroid cancer associated with the male gender is poorly explained.

Estimated change in prevalence of abnormal thyroid-stimulating hormone levels in China according to the application of the kit-recommended or NACB standard reference interval

BACKGROUND

Both the kit-recommended and United States National Academy of Clinical Biochemistry (NACB) standard thyroid-stimulating hormone (TSH) reference intervals (RIs) are used to determine thyroid dysfunction in clinical practice and epidemiological surveys in China. However, a number of kit-recommended RIs were derived from the European or United States reference population.

METHODS

A nationally representative cross-sectional study with 78,470 enrolled participants aged 18 years or older from China was performed. Serum concentrations of thyroid hormones, TSH, thyroid antibodies (by Roche Diagnostics), and urine iodine concentration (UIC) were measured.

FINDINGS

The abnormal TSH weighted prevalence was 15.33% (95% CI, 14.24% to 16.49%) according to the kit-recommended RI and 6.89% (6.46% to 7.34%) according to the NACB standard RI. The NACB standard prevalence of abnormal TSH was associated with an absolute change in abnormal TSH prevalence of -11.20% (-12.23% to -10.18%) among women. When estimating the proportion of supranormal TSH levels according to background characteristics, the NACB standard definition decreased the prevalence by more than 10% in some categories, with the highest absolute difference of -13.92% (-15.52% to -12.33%) observed among the elderly, -12.85% (-13.68% to -12.02%) among those with UIC ≥300 μg/L, and -12.15% (-13.02% to -11.28%) among non-smokers. For subnormal TSH, with the highest absolute difference of 3.17% (2.74% to 3.61%) observed among regular smokers, 3.11% (2.49% to 3.74%) among the elderly, and 2.53% (2.29% to 2.77%) among those with BMI <25.

INTERPRETATION

For adults in China, the NACB standard RI of TSH reveals a lower estimated prevalence of supranormal TSH levels than the kit-recommended RI. Because of the public health significance of overt and subclinical hypothyroidism and the very large population base in China, the TSH RI should be further assessed.

FUNDING

National Health Commission of the People's Republic of China and National Natural Science Foundation of China.

Reference Intervals for Serum Thyroid-Stimulating Hormone Based on a Recent Nationwide Cross-Sectional Study and Meta-Analysis

OBJECTIVE

The aim of our study was to compare the reference intervals (RIs) [median (2.5^th-97.5^th percentiles)] for thyroid-stimulating hormone (TSH) between subgroups stratified by ethnicity and iodine status in a global context.

DESIGN AND METHODS

Primary data were derived from a recently published cross-sectional study in mainland China. Secondary data were obtained from online databases. The RIs for TSH were calculated in the reference population according to the National Academy of Clinical Biochemistry (NACB) standard and in the disease-free population. A meta-analysis of ethnicity- and iodine status-specific TSH RIs was performed.

RESULTS

The primary data showed that the TSH RI (mU/L) in the disease-free population was 2.33 (0.67, 7.87), which is wider than the published RI [2.28 (0.74, 7.04)] in the reference population. The meta-analysis showed that whether in the reference or disease-free population, the RIs in Yellows were much higher than those in Caucasians. In the reference population, the median and 2.5^th percentile in the iodine-sufficient subgroup were both lower than the iodine-deficient or more-than-adequate subgroup, while the 97.5^th percentile showed a positive trend with increasing sufficiency of iodine. However, in the disease-free population, the iodine-sufficient subgroup had a lower median and 97.5^th percentile but higher 2.5^th percentile than the iodine-deficient subgroup.

CONCLUSION

Yellows have a higher TSH RI than Caucasians. In the reference population, both the median and 2.5^th percentile TSH in the iodine-sufficient population were the lowest among the different iodine status subgroups, while the 97.5^th percentile of TSH showed an upward trend with increasing iodine sufficiency.

Reference Intervals for Thyroid-Associated Hormones and the Prevalence of Thyroid Diseases in the Chinese Population

BACKGROUND

Thyroid diseases are highly prevalent worldwide, but their diagnosis remains a challenge. We established reference intervals (RIs) for thyroid-associated hormones and evaluated the prevalence of thyroid diseases in China.

METHODS

After excluding outliers based on the results of ultrasound screening, thyroid antibody tests, and the Tukey method, the medical records of 20,303 euthyroid adults, who visited the Department of Health Care at Peking Union Medical College Hospital from January 2014 to December 2018, were analyzed. Thyroid-associated hormones were measured by the Siemens Advia Centaur XP analyzer. The RIs for thyroid-associated hormones were calculated according to the CLSI C28-A3 guidelines, and were compared with the RIs provided by Siemens. The prevalence of thyroid diseases over the five years was evaluated and compared using the chi-square test.

RESULTS

The RIs for thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), total thyroxine (TT4), and total triiodothyronine (TT3) were 0.71-4.92 mIU/L, 12.2-20.1 pmol/L, 3.9-6.0 pmol/L, 65.6-135.1 nmol/L, and 1.2-2.2 nmol/L, respectively. The RIs of all hormones except TT4 differed significantly between males and females. The RIs of TSH increased with increasing age. The prevalence of overt hypothyroidism, overt hyperthyroidism, subclinical hypothyroidism, and subclinical hyperthyroidism was 0.5% and 0.8%, 0.2% and 0.6%, 3.8% and 6.1%, and 3.3% and 4.7% in males and females, respectively, which differed from those provided by Siemens.

CONCLUSIONS

Sex-specific RIs were established for thyroid-associated hormones, and the prevalence of thyroid diseases was determined in the Chinese population.

Subclinical thyroid dysfunction, bone mineral density, and osteoporosis in a middle-aged Korean population

Thyroid dysfunction is associated with the loss of bone density (osteoporosis). However, the connection between subclinical thyroid dysfunction and osteoporosis remains controversial. This study found no apparent association between subclinical hypothyroidism or subclinical hyperthyroidism and bone mineral density (BMD) in the lumbar spine and femur.

INTRODUCTION

The present study examined the relationship between subclinical thyroid dysfunction and BMD in healthy middle-aged adults.

METHODS

A total of 25,510 healthy Koreans with normal free thyroxine levels were enrolled from January 2011 to December 2016, and 91% of subjects visited only once. The average age of the 15,761 women was 45, and the average age of the 9749 men was 48. Levels of thyroid-stimulating hormone (TSH) and BMD were recorded in all subjects. BMD was measured using dual-energy X-ray absorptiometry.

RESULTS

No apparent association was found between subclinical thyroid dysfunction and BMD in the lumbar spine, femur-neck, and proximal femur sites compared with a euthyroid group. Age, body mass index (BMI), and postmenopausal status affected BMD in women, and only BMI affected BMD in men. Subclinical hypothyroidism was independently associated with a lower risk of osteoporosis (odds ratio 0.657, 95% confidence interval 0.464-0.930) in 4710 postmenopausal women.

CONCLUSIONS

No apparent association was found between subclinical hypothyroidism or subclinical hyperthyroidism defined on single TSH measurement and BMD at the lumbar spine and femur in a large cohort of middle-aged men and women. Subclinical hypothyroidism was independently associated with a lower risk of osteoporosis in postmenopausal women.

Evaluation of Thyroid Hormone Levels and Urinary Iodine Concentrations in Koreans Based on the Data from Korea National Health and Nutrition Examination Survey VI (2013 to 2015)

No nationwide data have been published about thyroid hormone levels and urinary iodine concentrations (UICs) in Korea. The Korea Centers for Disease Control and Prevention and the Korean Thyroid Association established a project to evaluate the nationwide thyroid hormone profile and UICs in healthy Koreans as part of the Korea National Health and Nutrition Examination Survey (KNHANES) VI (2013 to 2015), a nationwide, cross-sectional survey of the Korean population that enrolled 7,061 individuals who were weighted to represent the entire Korean population. Based on the KNHANES VI, the geometric mean value of serum thyroid stimulating hormone was 2.16 mIU/L, and its reference interval was 0.59 to 7.03 mIU/L. The mean value of serum free thyroxine was 1.25 ng/dL, and its reference interval was 0.92 to 1.60 ng/dL. The median UIC in the Korean population was reported to be 294 μg/L, corresponding to 'above requirements' iodine intake according to the World Health Organization recommendations. A U-shaped relationship of UIC with age was found. The prevalence of overt hyperthyroidism and overt hypothyroidism in the Korean population based on the KNHANES VI was 0.54% and 0.73%, respectively.

Circulating thyrotropin is upregulated by estradiol

After encountering two women with serum thyrotropin (TSH) levels greater in periovulatory phase than in other days of the menstrual cycle, we hypothesized that TSH levels could be sensitive to changes in circulating estrogens in women.

The objective of this study was to evaluate whether serum TSH increases after an induced acute increase of serum estradiol, and compare serum TSH increase with that of prolactin (PRL) which is a classic estradiol-upregulated pituitary hormone.

In this retrospective study, we resorted to stored frozen sera from 55 women who had undergone the GnRH agonist (buserelin)-acute stimulation test of ovarian steroidogenesis. This test, that is preceded by dexamethasone administration to suppress adrenal steroidogenesis, had been performed to show an increased buserelin-stimulated response of 17-hydroxyprogesterone, a response that is frequent in polycystic ovary syndrome. Fifty-five women had enough serum volume at pertinent times (first observation early in the follicular phase and all times of the test) to permit assay of serum estradiol, TSH and PRL.

Before dexamethasone administration, estradiol averaged 26.4 ± 15.5 pg/ml (reference range 23–139, follicular phase), TSH 1.78 ± 0.86 mU/L (reference range 0.3–4.2) and PRL 409.4 ± 356 mU/L (reference range 70.8–556) (mean ± SD).

Serum estradiol, TSH and PRL averaged 47.2 ± 27 pg/ml, 0.77 ± 0.48 mU/L and 246.4 ± 206.8 mU/L just prior to the buserelin injection, but they peaked at 253.4 ± 113.5 pg/ml (nv 83–495, midcycle), 3.30 ± 1.65 mU/L and 540.3 ± 695.2 mU/L after injection. The responses to buserelin of estradiol, TSH and PRL were of wide magnitude. There was a significant correlation between TSH peak and serum estradiol peak, betweeen AUC0-24 h-TSH and AUC0-24 h-estradiol, or between PRL peak and estradiol peak and AUC0-24 h -PRL and AUC0-24 h-estradiol in only a subgroup of women.

Therefore, women with estradiol-dependent increase in serum TSH do exist. Reference bands of serum TSH dependent on the phases of the menstrual cycle should be available.

Age- and gender-specific reference intervals of TSH and free T4 in an iodine-replete area: Data from Korean National Health and Nutrition Examination Survey IV (2013-2015)

BACKGROUND

Establishment of the reference interval of thyroid-stimulating hormone (TSH) is critical in the diagnosis of thyroid dysfunction and is affected by age, gender, iodine nutrition, and ethnicity. The aim of this study was to determine the reference intervals of TSH and free thyroxin (FT4) from a large, nationwide data of Korea where iodine intake is more than adequate.

METHODS

We analyzed data from the Korea National Health and Nutrition Examination Survey VI that measured serum TSH, FT4, and thyroid peroxidase antibody from 7,061 individuals (urinary iodine measurement in 6,565). Age- and gender-specific reference intervals were established from 95% confidence limits from the 2.5 to 97.5 percentile of TSH (log-transformed) and FT4 in reference populations.

RESULTS

The geometric mean of TSH was 2.16 ± 0.01 mIU/L, with the lowest value found in the middle aged group (2.04 ± 0.02 mIU/L) and higher values noted in age groups of 10-19 and over 70 years (2.38 ± 0.02 and 2.32 ± 0.07 mIU/L, respectively). The association of TSH and age was U-shaped. The overall reference interval of TSH was 0.59-7.03 mIU/L. Mean FT4 was 1.25 ± 0.003 ng/dL (16.09 ± 0.039 pmol/L), and it showed a small but continuous decrease after 20 years of age (P < 0.001). There was a significant positive correlation between TSH and urine iodine concentration (r = 0.154, P < 0.001).

CONCLUSIONS

The reference interval of TSH in Korea, where iodine intake is above the requirement, was 0.59-7.03 mIU/L and showed U-shaped change with age, which was a similar pattern to iodine intake. The reference interval of FT4 was 0.92-1.60 ng/dL. The geometric mean and upper limit of TSH were higher than those of Western populations, reflecting the paramount importance of iodine intake on thyroid function.

The Relationship between Subclinical Thyroid Disease and Cardiovascular Disease Risk Score in Koreans

Subclinical hyperthyroidism and subclinical hypothyroidism are characterized by abnormal thyroid stimulating hormone (TSH) with normal free thyroxine. Subclinical thyroid diseases, to date, have received less attention compared with other thyroid diseases since they are asymptomatic. This study aimed to verify the association between subclinical thyroid diseases and cardiovascular diseases (CVDs) risk score in the Korean population. This was a population-based cohort study using data collected from 3,722 subjects (aged ≥ 30 years) during the 6th Korea National Health and Nutrition Examination Survey (KNHANES VI; 2013-2015). Gender-specific Framingham risk scores were calculated to identify the association between subclinical thyroid diseases and 10-year CVD risk score. Complex survey, with consideration of sampling weight, was analyzed using generalized linear models after stratification by gender. The TSH reference range was between 0.61 and 6.91 mIU/L in this study. TSH showed a positive association with the 10-year CVD risk score only in the female population (P = 0.001). There were significant differences in the least squares means of 10-year CVD risk score by the effect of subclinical hypothyroidism compared with euthyroidism (normal group) in females, after adjusting for body mass index, white blood cell, and urine iodine (P = 0.006 and Bonferroni corrected P = 0.012). In conclusion, subclinical hypothyroidism is associated with increased 10-year CVD risk score in the female Korean population aged 30 years or more. Therefore, we recommend to clinically checkup major CVD risk factors in female patients with subclinical hypothyroidism aged 30 years or more.

TSH cut off point based on depression in hypothyroid patients

BACKGROUND

The prevalence of depressive symptoms in hypothyroidism is high. Considering that hypothyroidism and depression share some clinical features, some researchers use the "brain hypothyroidism" hypothesis to explain the pathogenesis of depression. We aimed to detect a new TSH cut-off value in hypothyroidism based on depression symptoms.

METHODS

A cross-sectional study was conducted on hypothyroid patients referred to endocrine clinics. Individuals who had developed euthyroid state under treatment with levothyroxine with TSH levels of 0.5-5 MIU/L with no need for dosage change were included in the study. After comprehensive history taking, laboratory tests including TSH, T4 and T3 were performed. Beck depression questionnaire was completed for all patients by trained interviewers. TSH cut-off values based on depression was determined by Roc Curve analysis.

RESULTS

The participants were 174 hypothyroid patients (Female; 116: 66.7%, Male; 58: 33.3%) with mean age 45.5 ± 11.7 (19-68) years old. Based on Beck depression test, scores less than 10 was considered healthy and more than 10 were considered depressed. According to Roc curve analysis, the optimal cut- off value of TSH was 2.5 MIU/L with 89.66% sensitivity. The optimal TSH cut- off based on severe depression was 4 MIU/L.

CONCLUSION

The present study suggests that a clinically helpful TSH cut-off value for hypothyroidism should be based on associated symptoms, not just in population studies. Based on the assessment of depression, our study concludes that a TSH cutofff value of 2.5 MIU/L is optimal.

Age-specific reference interval of serum TSH levels is high in adolescence in an iodine excess area: Korea national health and nutrition examination survey data

PURPOSE

Serum thyroid-stimulating hormone level was influenced by several factors, including age, gender, thyroid auto-antibodies, race, and intake of dietary iodine. We evaluated age-specific reference interval of serum thyroid-stimulating hormone levels in Korea, an iodine excess area.

METHODS

This nationwide population-based cross-sectional study included representative civilian, non-institutional population (n = 6564) who underwent thyroid function tests from Korea National Health and Nutrition Examination Survey VI (2013-2015). The reference interval of serum thyroid-stimulating hormone levels was defined between the 2.5th and 97.5th percentiles in the reference population.

RESULTS

The geometric mean of serum thyroid-stimulating hormone levels in the reference population was 2.17 mIU/L with a reference interval of 0.62-6.84 mIU/L. In the reference population, the geometric mean of serum TSH levels in each age group of 10-18, 19-29, 30-39, 40-49, 50-59, 60-69, and equal or older than 70 years was 2.47, 2.20, 2.07, 2.04, 2.23, 2.12, and 2.27 mIU/L, with a reference interval of 0.74-7.35, 0.67-6.42, 0.63-6.04, 0.62-6.20, 0.56-7.37, 0.57-6.90, and 0.42-6.58 mIU/L, respectively. In the reference population, the urinary iodine concentrations were consistently high in all age groups (median 298.5 μg/L). Subjects aged 10-18 years had the highest urinary iodine concentrations.

CONCLUSIONS

There was no shift toward higher levels with age in the distribution of serum thyroid-stimulating hormone levels. The reference interval of serum thyroid-stimulating hormone levels was consistently high in all age group, especially from adolescence 10-18 years in a Korean population who had excessive intake of dietary iodine.

Excessive Iodine Intake and Thyrotropin Reference Interval: Data from the Korean National Health and Nutrition Examination Survey

BACKGROUND

Iodine intake is associated with various thyroid diseases and serum thyrotropin (TSH) levels. The aim of this study was to investigate iodine intake and its impact on the distribution of serum TSH levels using nationwide data from Korea, a country known to be iodine replete.

METHODS

The sixth Korean National Health and Nutrition Examination Survey (2013-2015) is a nationwide, cross-sectional survey of the Korean general population. Participants were selected using two-stage stratified cluster sampling of the population and housing census data. A total of 6564 participants aged ≥10 years who underwent thyroid function tests and urinary iodine level measurements during the survey were included in this study.

RESULTS

The median urinary iodine concentration (UIC) was 299.3 μg/L (interquartile range 158.8-699.8), suggesting more than adequate iodine intake in Korea. With high-iodine intake in all age groups and in both females and males, the TSH reference interval in the Korean reference population was right-shifted at 0.62-6.84 mIU/L. The prevalence of overt and subclinical hypothyroidism in Korea according to this reference interval was 0.73% and 3.12%, respectively, and was significantly associated with nutritional iodine status (p = 0.011 and p < 0.001, respectively).

CONCLUSIONS

This first nationwide survey demonstrates more than adequate iodine intake and a right-shifted distribution of serum TSH levels in the Korean general population. Nutritional iodine status is important for determining serum TSH levels and is associated with a high prevalence of hypothyroidism. Nutritional iodine status might need to be considered when establishing TSH reference intervals of populations in iodine-replete areas.

Thyroid Stimulating Hormone Reference Range and Prevalence of Thyroid Dysfunction in the Korean Population: Korea National Health and Nutrition Examination Survey 2013 to 2015

BACKGROUND

No nationwide epidemiological study evaluating the prevalence of subclinical and overt forms of hypothyroidism and hyperthyroidism has yet been conducted in Korea. This study aimed to evaluate the reference range of serum thyroid stimulating hormone (TSH) and the national prevalence of thyroid dysfunctions in Korea.

METHODS

Nation-wide cross-sectional data were analyzed from a representative sample of the civilian, non-institutionalized Korean population (n=6,564) who underwent blood testing for thyroid function and anti-thyroid peroxidase antibody (TPOAb) as part of the Korea National Health and Nutrition Examination Survey VI (2013 to 2015).

RESULTS

The reference interval of serum TSH in the Korean reference population was 0.62 to 6.68 mIU/L. Based on this reference interval, the prevalence of overt and subclinical hypothyroidism was 0.73% (males 0.40%, females 1.10%) and 3.10% (males 2.26%, females 4.04%), respectively. The prevalence of hypothyroidism increased with age until the age group between 50 to 59 years. Positive TPOAb were found in 7.30% of subjects (males 4.33%, females 10.62%). The prevalence of overt and subclinical hypothyroidism TPOAb-positive subjects was 5.16% and 10.88%, respectively. The prevalence of overt and subclinical hyperthyroidism was 0.54% (males 0.30%, females 0.81%) and 2.98% (males 2.43%, females, 3.59%), respectively.

CONCLUSION

The Serum TSH reference levels in the Korean population were higher than the corresponding levels in Western countries. Differences were found in the prevalence of hypothyroidism and hyperthyroidism according to age, sex, and TPOAb positivity. This study provides important baseline information for understanding patterns of thyroid dysfunction and diseases in Korea.