Age-specific TSH reference ranges have minimal impact on the diagnosis of thyroid dysfunction

Diagnosing and treating the elderly individual with hypopituitarism

Hypopituitarism in the elderly is an underestimated condition mainly due to the non-specific presentation that can be attributed to the effects of aging and the presence of comorbidities. Diagnosis and treatment of hypopituitarism often represent a challenging task and this is even more significant in the elderly. Diagnosis can be insidious due to the physiological changes occurring with aging that complicate the interpretation of hormonal investigations, and the need to avoid some provocative tests that carry higher risks of side effects in this population. Treatment of hypopituitarism has generally the goal to replace the hormonal deficiencies to restore a physiological balance as close as possible to that of healthy individuals but in the elderly this must be balanced with the risks of over-replacement and worsening of comorbidities. Moreover, the benefit of some hormonal replacement therapies in the elderly, including sex hormones and growth hormone, remains controversial.

Epidemiology, Types, Causes, Clinical Presentation, Diagnosis, and Treatment of Hypothyroidism

Hypothyroidism means an underactive thyroid gland. This leads to a decrease in the functioning of the thyroid gland. It is a very common endocrine disorder that causes under-secretion of thyroid hormones, mainly thyroxine (T4) and triiodothyronine (T3). It affects people of every age group but is more commonly found in women and older people. The symptoms of hypothyroidism can go unnoticed, may not be specific, and may overlap with other conditions, which makes it harder to diagnose it in some cases. Common symptoms include fatigue, weight gain, increased sensitivity to cold (cold intolerance), irregular bowel movements (constipation), and dry skin (xeroderma). These conditions are mostly the result of a low metabolic rate in the body. Weight gain occurs due to a decrease in fat-burning rate and cold intolerance due to a decrease in heat production by the body. This condition can be caused by a variety of factors, including autoimmune diseases, radiation therapy, thyroid gland removal surgeries, and certain medications. The diagnosis of hypothyroidism is based on laboratory tests that measure the levels of thyroid hormones (T3 and T4) in the blood. Treatment typically involves lifelong hormone replacement therapy with synthetic thyroid hormone replacement medication, such as levothyroxine, to help regulate hormone levels in the body. People with hypothyroidism may need to have their medication dosage adjusted over time. If hypothyroidism is left untreated, it can lead to severe complications like mental retardation, delayed milestones, etc., in infants and heart failure, infertility, myxedema coma, etc., in adults. With appropriate treatment, the symptoms of hypothyroidism can be effectively managed, and most people with the condition can lead normal, healthy lives. Lifestyle modifications like eating healthy food and exercising regularly can help manage the symptoms and improve the quality of life.

Reference intervals for serum TSH concentrations of healthy children from the Central Region of Brazil

Objective

The objective of this study was to determine the serum thyroid-stimulating hormone (TSH) concentration reference intervals (RIs) of healthy children aged 1 to 10 years of both sexes, living in the Central Region of Brazil.

Subjects and methods

1,735 children [869 (50.1%) female; 866 (49.9%) male] enrolled in the morning shift of 47 pre- and 83 public elementary schools in the municipality of Cuiabá, Mato Grosso, were studied by gathering anthropometric and social data and their medical history. A blood sample was collected from each child to determine the TSH concentration using the electrochemiluminescence method on a Cobas® 6000 modular analyzer (Analyzer series, Roche Diagnostics).

Results

The RIs were determined using the 2.5 and 97.5 percentile and the mean ± 2 standard deviations methods. After identifying the homoscedastic groups by age and sex, outliers higher or lower than three standard deviations were excluded. The distribution of serum TSH concentrations showed no significant age or sex differences. Based on the percentile method, TSH RI ranged from 0.93 to 5.86 μIU/mL. Based on the mean ± 2 standard deviations, TSH RI ranged from 0.30 to 5.29 μIU/mL.

Conclusion

The normal serum TSH concentration of the Brazilian children evaluated in this study differ from those of populations from other countries. Other regional population studies may validate the RIs found in this study and enable its safer use in pediatric clinical practice.

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.

Variation in the reference range limits of thyroid function tests and association with the prevalence of levothyroxine treatment

Many individuals with marginally abnormal thyroid function test (TFT) results may be treated and it is unknown if the limits of the thyrotropin (TSH) and free thyroxine (FT4) reference intervals reported alongside the laboratory results are associated with the prevalence of levothyroxine treatment. We obtained information regarding reported TFT reference intervals from UK National Health Service (NHS) laboratories and evaluated its relationship with the prevalence of levothyroxine treatment for corresponding health areas for 2014. The upper limit of serum TSH was significantly, linearly, independently, and negatively associated with prevalent levothyroxine treatment: -0.54% (95% CI, -0.68% to -0.40%). The lower limit of serum FT4 was significantly and independently associated with the prevalence of levothyroxine treatment in a non-linear (J-shaped) manner with an increase being noted from a FT4 level of ≈9.5 pmol/L onwards. We conclude that minor changes in the reference range limits for serum TSH and FT4 are associated with levothyroxine treatment.

The management and metabolic characterization: hyperthyroidism and hypothyroidism

Hyperthyroidism and hypothyroidism are common diseases resulting from thyroid dysfunction, and are simple to diagnose and treat. The traditional treatment for hypothyroidism is thyroid hormone replacement therapy. The traditional treatments for hyperthyroidism include antithyroid drug, iodine radiotherapy, and surgery. Thyroid disease can be fatal in severe cases if untreated. Current statistical reference ranges used for diagnosis based on relevant biochemical parameters have been debated, and insufficient treatment can result in long-term thyroid hormone deficiency, which is associated with increased risk of cardiovascular disease and persistent symptoms. In contrast, overtreatment can result in heart disease and osteoporosis, particularly in older people and pregnant women. Therefore, under- or over-treatment should be avoided and treatment regimens should be monitored closely. A significant proportion of patients who achieve biochemical treatment goals still complain of significant symptoms. Systematic literature review was performed through the Embase (Elsevier), PubMed and Web of Science databases, and studies summarized evidence regarding treatment and management of hypothyroidism and hyperthyroidism, and reviewed clinical practice guidelines. We also reviewed the latest research on the metabolic mechanisms of hyperthyroidism and hypothyroidism, which contributed to understanding of thyroid diseases in the clinic. A reliable algorithm is needed to management, assessment, and treatment patients with hyperthyroidism and hypothyroidism, which can not only improve management efficiency, but also providing a broad application. In addition, the thyroid disorder showed a lipid metabolism tissue specificity in the Ventromedial Hypothalamus, and effect oxidative stress and energy metabolism of whole body. This review summarizes an algorithm for thyroid disease and the latest pathogenesis that would be useful to generalist and subspecialty physicians and others providing care for patients with this condition.

Hypothyroidism: The difficulty in attributing symptoms to their underlying cause

Common symptoms of overt hypothyroidism are non-specific and include fatigue, lethargy, and dry skin. Although the diagnosis is considered to be straightforward, no single symptom can be used to identify patients with overt hypothyroidism, while many patients with subclinical hypothyroidism are asymptomatic. A large population-based study on the spectrum of symptoms in subclinical hypothyroidism showed similar rates of thyroid disease-related symptoms compared with euthyroid subjects, while the TSH concentration had no impact on symptom score. Together, these findings make it challenging to attribute symptoms to their underlying cause. This is also true in the case of unexplained persistent symptoms in levothyroxine-treated patients. Although generally considered a life-long replacement therapy, successful thyroid hormone discontinuation resulting in euthyroidism has been reported in approximately one third of patients. Thus, we overtreat patients with (subclinical) hypothyroidism, highlighting the importance of reliable diagnostic criteria. The diagnostic process, including the implementation of robust TSH and FT4 reference intervals, is especially challenging in specific situations including aging, pregnancy, non-thyroidal illness, and central hypothyroidism. There is a clear need for improved adherence to current guidelines from scientific societies and for willingness to manage symptoms without a clear pathological correlate, especially in the case of mild TSH elevations. This review will highlight recent literature on this topic and offers some practice points.

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 across the Lifespan: Do Age-Related Changes Matter?

Circulating concentrations of thyrotropin (TSH) and thyroxine (T4) are tightly regulated. Each individual has setpoints for TSH and free T4 which are genetically determined, and subject to environmental and epigenetic influence. Pituitary-thyroid axis setpoints are probably established in utero, with maturation of thyroid function continuing until late gestation. From neonatal life (characterized by a surge of TSH and T4 secretion) through childhood and adolescence (when free triiodothyronine levels are higher than in adults), thyroid function tests display complex, dynamic patterns which are sexually dimorphic. In later life, TSH increases with age in healthy older adults without an accompanying fall in free T4, indicating alteration in TSH setpoint. In view of this, and evidence that mild subclinical hypothyroidism in older people has no health impact, a strong case can be made for implementation of age-related TSH reference ranges in adults, as is routine in children.

Establishment of Reference Intervals for Thyroid-Associated Hormones Using refineR Algorithm in Chinese Population at High-Altitude Areas

Objectives

Diagnosis of thyroid disease among individuals dwelling at high altitude remains a challenge. Reference intervals (RIs) for thyroid-associated hormones among Tibetans living at various high altitudes were established to improve diagnosis.

Methods

One thousand two hundred eighty-one subjects were randomly recruited from Nyingchi, Shigatse/Lhasa, and Ali of Tibet. Thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were measured by the Cobas e601 electrochemiluminescence analyzer. We used multiple linear regression and variance component analysis to assess the effect of sex, age, and altitude on hormones. RIs were established by refineR algorithm and compared with those provided by the manufacturer.

Results

Serum TSH was significantly lower in males than in females, while FT3 and FT4 were higher in males. Both FT3 and FT4 decreased with increasing age. FT3 increased with altitude, while TSH and FT4 were less influenced by altitude. The RI for TSH was 0.764–5.784 μIU/ml, while for FT4, the RIs were 12.36–19.38 pmol/L in females and 14.84–20.18 pmol/L in males. The RIs for FT3 at Nyingchi, Shigatse/Lhasa, and Ali in females were 4.09–4.98, 4.31–5.45, and 4.82–5.58 pmol/L, while in males, the values were 4.82–5.41, 4.88–5.95, and 5.26–6.06 pmol/L, respectively. The obtained RIs for TSH and FT4 were generally higher, while that for FT3 was narrower than the RIs provided by Cobas.

Conclusions

Specific RIs were established for thyroid-associated hormones among Tibetans, which were significantly different from those provided by the manufacturer.

Factors influencing the reference interval of thyroid-stimulating hormone in healthy adults: A systematic review and meta-analysis

BACKGROUND

Many studies have reported that the thyroid-stimulating hormone (TSH) reference interval is susceptible to external factors, such as age, sex, race, region and iodine intake. However, no meta-analysis has comprehensively explored the effect of these factors on the TSH reference interval.

METHODS

Articles published from January 1960 to January 2020 were searched in PubMed, Embase, Cochrane, Scopus, Medline English databases and CNKI, WanFang and CQVIP Chinese databases. In total, 19 studies were ultimately included. All data were analysed using Review Manager 5.3, STATA 16.0 software, GraphPad Prism 8.0 and Microsoft Excel 2010 to draw the TSH concentration curve.

RESULTS

The TSH reference interval was significantly influenced by sex and age. The mean of TSH concentration in females was 0.27 mIU/L higher than that in males. Reference interval of TSH is divided into 20-59 years old and >60 years old age groups in males, and 20-39 years old and >40 years old age groups in females. Regardless of sex, TSH concentrations all increase with age. In iodine-deficient areas, TSH reference intervals were generally lower than those in iodine-sufficient or iodine-excessive areas. The TSH reference interval in Asia and North American countries was generally higher than that in most European countries. In the subgroup analyses of sample size, region and assay methods and manufacturers, the between-group differences were significant.

CONCLUSION

The TSH reference interval was significantly influenced by sex, age, iodine intake, sample size, region, and assay methods and manufacturers, but other factors should not be ignored. Therefore, it is necessary for each laboratory to validate an appropriate TSH reference interval based on local conditions.

Association between Subclinical Hypothyroidism and Incident Hypertension in Women: A Systematic Review and Meta-Analysis

Subclinical hypothyroidism (SCH) has been found to be associated with an increased risk of cardiovascular diseases. However, there is no clear consensus on the relationship between SCH and hypertension (HTN). We sought to investigate the association between SCH and incident HTN in women. MEDLINE and EMBASE databases were searched for studies that reported the incidence of HTN in females with SCH versus without SCH. Pooled odds ratio (OR) and 95% confidence interval (CI) of the outcome were obtained using a random-effects model. Studies were also divided into the middle-aged (mean age < 65) and the older (mean age ≥ 65) subgroups, and a subgroup analysis was performed to examine the potential age-effect on the association between SCH and HTN. Nine studies with a total of 21,972 subjects met the inclusion criteria. SCH was found to be positively associated with HTN (OR = 1.32, 95% CI = 1.02–1.71). Such association varied depending on the age of women. In the middle-aged subgroup, SCH was more positively associated with HTN (OR = 1.64, 95% CI = 1.18–2.27), while there was no significant association in the older subgroup (OR = 0.97, 95% CI = 0.80–1.16). Our study showed that the middle-aged females with SCH had an increased risk of HTN, while there was no significant association in the older females with SCH.

Prevalence, predictors and outcomes of thyroid dysfunction in patients with acute myocardial infarction: the ThyrAMI-1 study

PURPOSE

Thyroid dysfunction in patients with cardiac disease is associated with worse outcomes. This study aimed to evaluate the prevalence and analyse predictors and outcomes of thyroid dysfunction in patients presenting with an acute myocardial infarction (AMI).

METHODS

A prospective multicentre observational study of patients recruited from six acute hospitals within the North of England. Consecutive patients without previous thyroid disease presenting with both ST-elevation AMI (STEMI) and non-ST-elevation AMI (NSTEMI) were recruited to the Thyroxine in Acute Myocardial Infarction 1 (ThyrAMI-1) cohort study between December 2014 and 2016. Thyroid profile, standard biochemistry measurements and demographic information were obtained within 12 h of admission to hospital. Multivariable logistic regression analyses were performed to assess the predictors of thyroid dysfunction and Cox proportional hazards analyses were utilised to compare all-cause mortality by categories of thyroid dysfunction up to June 2019.

RESULTS

Of the 1802 participants analysed, 1440 (79.9%) were euthyroid, 312 (17.3%) had subclinical hypothyroidism (SCH), 22 (1.2%) had subclinical hyperthyroidism (SHyper) and 25 (1.3%) had low T3 syndrome (LT3S). Predictors for SCH were increasing age, female sex, higher thyroid peroxidase antibody (TPOAb) levels, higher serum creatinine levels and early morning sampling time (between 00:01-06:00 h). The predictors of SHyper were lower body mass index and afternoon sampling time (between 12:01 and 18:00 h). Predictors of LT3S were increasing age, higher creatinine levels and presence of previous ischaemic heart disease. Compared to the euthyroid group, patients with LT3S had higher all-cause mortality; adjusted hazard ratio (95% CI) of 2.02 (1.03-3.95), p = 0.04, whereas those with SCH and SHyper did not exhibit significantly increased mortality; adjusted hazard ratios (95% CI) of 1.05 (0.74-1.49), p = 0.79 and 0.27 (0.04-1.95), p = 0.19, respectively.

CONCLUSIONS

Thyroid dysfunction is common in AMI patients on admission to hospital and our data provide an understanding regarding which factors might influence thyroid dysfunction in these patients. Furthermore, the negative association between LT3S and increased mortality post-AMI has once again been highlighted by this study. More research is required to assess if treatment of thyroid dysfunction improves clinical outcomes.

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.

Study of reference intervals for free triiodothyronine, free thyroxine, and thyroid-stimulating hormone in an elderly Chinese Han population

The clinical manifestations of thyroid diseases in elderly patients are often atypical. This study aimed to establish reference intervals for thyroid function in the elderly in order to help diagnose thyroid diseases in this population. A total of 5345 healthy individuals were examined and divided into three groups according to their age: 4297 individuals aged < 65 years (19–64), 719 individuals aged between 65 and 79 years, and 329 individuals aged between 80 and 100 years. Levels of free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), thyroid peroxidase antibody, and thyroglobulin antibody were measured in these subjects by using a fully automated analyzer. The following free triiodothyronine, free thyroxine, and thyroid-stimulating hormone reference intervals were obtained from each age group: For individuals aged < 65 years (19–64 years), FT3, FT4, and TSH were 3.40–6.44, 10.26–19.25 pmol/L and 0.50–4.81 μIU/mL, respectively. For individuals aged between 65 and 79 years, FT3, FT4 and TSH ranged between 3.01–5.91, 10.04–19.76 pmol/L, and 0.54–5.51 μIU/mL, respectively. For individuals aged between 80 and 100 years, FT3, FT4, and TSH varied between 2.82–5.57, 9.79–21.22 pmol/L, 0.31–6.28 μIU/mL respectively. FT3 concentration was lower and the concentrations of FT4 and TSH were higher in individuals aged ≥ 65 years than in those aged <65 years (P<0.0001; P = 0.0039; P<0.0001, respectively). In conclusion, establishment of a reference interval would allow clinicians to diagnose diseases more accurately and easily.

Changes in Thyroid Function Across Adolescence: A Longitudinal Study

OBJECTIVE

There are no large, longitudinal studies of thyroid function across adolescence. The aims of this study were to examine longitudinal trends in thyrotropin (TSH), free triiodothyronine (fT3) and free thyroxine (fT4) and determine age-specific reference ranges.

METHODS

Thyroid function was assessed in 3415 participants in the Brisbane Longitudinal Twin Study at ages 12, 14, and 16, using the Abbott ARCHITECT immunoassay. Longitudinal analyses were adjusted for body mass index and puberty.

RESULTS

In girls, mean fT4 (± SE) increased between age 12 and 14 (by 0.30 ± 0.08 pmol/L; P < 0.001), while remaining unchanged in boys; from age 14 to 16, fT4 increased in both girls (by 0.42 ± 0.07 pmol/L; P < 0.001) and boys (0.64 ± 0.07 pmol/L, P < 0.001). There was a slight increase in fT3 from age 12 to 14 years in girls (by 0.07 ± 0.03 pmol/L; P = 0.042), with a more marked increase in boys (0.29 ± 0.03 pmol/L; P < 0.001), followed by a decrease from age 14 to 16 in both sexes (girls, by 0.53 ± 0.02 pmol/L; P < 0.001; boys, by 0.62 ± 0.03 pmol/L; P < 0.001). From age 12 to 14, TSH showed no significant change in girls or boys, then levels increased from age 14 to 16 in both sexes (in girls, by 4.9%, 95% CI: 2.4%-10.3%, P = 0.020; in boys, by 7.2%, 95% CI: 3.0%-11.6%, P = 0.001). Reference ranges differed substantially from adults, particularly for fT4 and fT3.

CONCLUSIONS

Thyroid function tests in adolescents display complex, sexually dimorphic patterns. Implementation of adolescence-specific reference ranges may be appropriate.

Sample Timing, Diagnosis of Subclinical Thyroid Dysfunction and Mortality in Acute Myocardial Infarction: ThyrAMI1 Study

OBJECTIVE

The objective of this study was to determine the impact of blood sample timing on the diagnosis of subclinical thyroid dysfunction (SCTD) and mortality in patients with acute myocardial infarction (AMI).

PATIENTS, DESIGN, AND MAIN OUTCOME MEASURES

Patients with AMI had thyroid function evaluated on admission between December 2014 and December 2016 and those with abnormal serum thyrotropin (TSH) had repeat thyroid function assessed at least a week later. The association between sample timing and SCTD was evaluated by logistic regression analysis. Secondary outcomes were confirmation of SCTD on repeat testing and all-cause mortality up to June 2018.

RESULTS

Of the 1806 patients [29.2% women, mean (± standard deviation) age of 64.2 (±12.1) years] analyzed, the prevalence of subclinical hypothyroidism (SCH) was 17.2% (n = 311) and subclinical hyperthyroidism (SHyper) was 1.2% (n = 22) using a uniform TSH reference interval. The risk of being diagnosed with SCTD varied by sample timing in fully-adjusted models. The risk of SCH was highest between 00.01 and 06.00 hours and lowest between 12.01 and 18.00 hours, P for trend <.001, and risk of SHyper was highest between 12.01 hours and 18.00 hours and lowest between 00.01 hours and 06.00 hours. Furthermore, time of the initial sample was associated with the risk of remaining in a SCH state subsequently. Mortality in SCH patients was not elevated when a uniform TSH reference interval was utilized. However, when time period-specific TSH reference ranges were utilized, the mortality risk was significantly higher in SCH patients with HR (95% CI) of 2.26 (1.01-5.19), P = .04.

CONCLUSIONS

Sample timing impacts on the diagnosis and prognosis of SCH in AMI patients. If sample timing is not accounted for, SCH is systemically misclassified, and its measurable influence on mortality is lost.

Age- and Sex-Specific TSH Upper-Limit Reference Intervals in the General French Population: There Is a Need to Adjust Our Actual Practices

It is well known that thyroid dysfunction increases with age. This study is aimed to determine reference intervals, in males and females, suitable for thyroid disease exploration during adult life using routinely collected serum thyrotropin (TSH) data in a tertiary center from 2007 to 2018. Over 11 years, 295,775 TSH levels were measured in a single lab. Among the 156,025 TSH results available for analysis, 90,538 values were from female subjects, 82,019 were from patients aged >60 years and 26,825 were from patients aged >80 years. By using an indirect approach, we determined reference values of TSH adapted to age and sex, and we then evaluated the proportion of patients who would have been reclassified with these reference values. The median TSH ranged from 1.2–1.4 mUI/L during the study period. The upper limit of reference range of TSH increased with age; in females the median to 97.5th percentile values increased continuously from the age of 30 years to the oldest age group. Using new calculated reference values in patients with TSH above the conventional upper-limit reference value (4 mUI/L), the proportion of results reclassified as within the reference interval among patients aged >60 years ranged, according to age group, from 50.5% to 65.1% of females and from 33.0% to 37.7% of males. The use of TSH age-specific and sex-specific upper-limit reference values led to the reclassification of a great number of samples, notably among women. This suggests that age-specific TSH upper-limit reference intervals in daily practice should be used in order to avoid misclassification.

Reference intervals for thyroid-stimulating hormone, free thyroxine, and free triiodothyronine in elderly Chinese persons

Background Thyroid hormone levels are essential for diagnosing and monitoring thyroid diseases. However, their reference intervals (RIs) in elderly Chinese individuals remain unclear. We aimed to identify factors affecting thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) levels using clinical "big data" to establish hormone level RIs for elderly Chinese individuals. Methods We examined 6781, 6772, and 6524 subjects aged ≥65 years who underwent FT3, FT4, and TSH tests, respectively, at the Peking Union Medical College Hospital between September 1, 2013, and August 31, 2016. Hormones were measured using an automated immunoassay analyzer (ADVIA Centaur XP). RIs were established using the Clinical Laboratory Standards Institute document C28-A3 guidelines. Results The median TSH was significantly higher in women than in men; the opposite was true for median FT3 and FT4 levels. No differences were observed in TSH or FT4 by age in either sex or overall; FT3 levels significantly decreased with age. Seasonal differences were observed in TSH and FT3 levels but not FT4 levels; the median TSH was the highest in winter and lowest in summer, whereas the median FT3 was the lowest in summer (albeit not significantly). RIs for TSH were 0.53-5.24 and 0.335-5.73 mIU/L for men and women, respectively; those for FT3 were 3.76-5.71, 3.60-5.42, and 3.36-5.27 pmol/L in 64- to 74-, 75- to 84-, and 85- to 96-year-old subjects, respectively. The RI for FT4 was 11.70-20.28 pmol/L. Conclusions RIs for TSH in elderly individuals were sex specific, whereas those for FT3 were age specific.

Relationship of gender and age on thyroid hormone parameters in a large Chinese population

Objective This study aimed to present the impact of age and gender on thyroid hormone levels in a large Chinese population with sufficient iodine intake. Subjects and methods A total of 83643 individuals were included and were stratified by age and gender. The median, 2.5th and 97.5th of thyrotropin (TSH), free triiodothyronine (FT3), free thyroxine (FT4) and FT3/FT4 ratio were calculated for both genders for every decade from 18 to over 80 years. TSH, FT3, FT4, FT3/FT4 distribution in each age group was evaluated for females and males using smoothing splines in the generalized additive models (GAM). TSH concentrations were compared in the different age groups in gender. Results In the over 80s age group, the TSH level (median: 2.57 mIU/L, 2.5th-97.5th: 0.86-7.56 mIU/L) was significantly higher than other age groups, irrespective to gender (P<0.001). Females had a higher TSH value than males in all age groups (P<0.001). Results of the smoothing curves showed that TSH increased with age, FT3 concentration was higher in males than in females and the tendency of the FT3/FT4 ratio was basically similar to that of FT3. TSH concentration in the 50s age group (median 2.48 mIU/L for females versus 2.00 mIU/L for males) was significantly higher than that in the 30s age group (median 2.18 mIU/L for females versus median 1.85 mIU/L for males). Conclusions In accord with increasing TSH values during aging, females and older adults have lower FT3 values and lower FT3/FT4 ratios, while the FT4 values remain stable.

Reference intervals in the diagnosis of thyroid dysfunction: treating patients not numbers

Although assigning a diagnosis of thyroid dysfunction appears quite simple, this is often not the case. Issues that make it unclear whether thyroid function is normal include transient changes in thyroid parameters, inter-individual and intra-individual differences in thyroid parameters, age-related differences, and ethnic variations. In addition, a statistically calculated distribution of thyroid analytes does not necessarily coincide with intervals or cutoffs that have predictive value for beneficial or adverse health outcomes. Based on current clincial trial data, it is unclear which individuals with mild thyroid-stimulating hormone elevations will benefit from levothyroxine treatment. For example, only a small number of patients with thyroid-stimulating hormone values of more than 10 mIU/L have been studied in a randomised manner. Even if therapy is initiated for abnormal thyroid function, not all treated individuals are maintained at the desired treatment target, and therefore might still be at risk. The consequence of this is that each patient's thyroid function needs to be assessed on an individual basis with the entire clinical picture in mind. Monitoring also needs to be vigilant, and the targets for treatment reassessed continually.

Subclinical Hypothyroidism: is it Really Subclinical with Aging?

No recent study has focused on clinical features of subclinical hypothyroidism (SCH), especially in older patients. TSH measurement has remarkably evolved these last 20 years and thus reconsideration is needed. In our prospective multicenter study (2012-2014) including 807 subjects aged <60 years (<60y) and 531 subjects ≥60 years (≥60y), we have monitored 11 hypothyroidism-related clinical signs (hCS) together with TSH, FT4, FT3 and anti-thyroperoxidase antibodies values. hCS expression has been compared in patients with SCH vs euthyroidism in each age group. The number of hCS above 60y of age were found to be more elevated in the euthyroid population (1.9 vs 1.6, p<0.01) than in the SCH population (2.3 vs 2.6, p=0.41) while increase in hCS is limited to SCH subjects in the <60y group (p<0.01). The percentage of subjects with at least 3 signs increased with SCH in the <60y group (42.6% vs 25.0%, p<0.01) but not ≥60y (34.4% vs 33.9%, p=0.96). In older individuals, only three hCS could be related to both SCH and a decreased T3/T4-ratio (0.26 vs 0.27, p<0.01), suggesting either a reduced activity of TSH, or an adaptive response with aging. While hCS are clearly associated with SCH in patients <60y, they are not so informative in older subjects. TSH measurements carried out on the basis of hCS need to be interpreted with caution in aged patients. A reassessment of the TSH reference range in older patients is clearly needed and should be associated to more appropriate monitoring of thyroid dysfunction

Overtime trend of thyroid hormones and thyroid autoimmunity and ovarian reserve: a longitudinal population study with a 12-year follow up

BACKGROUND

Ovarian reserve, vital for reproductive function, can be adversely affected by thyroid diseases. Despite alternations of thyroid hormones with ageing, data on interactions between the overtime trend of thyroid functions and ovarian reserve status has rarely been reported. We aimed to examine the overtime trend of thyroid hormones, thyroid peroxidase antibody (TPO Ab) and their associations with ovarian reserve status, identified by levels of age specific anti-mullerian hormone (AMH) in reproductive aged women, who participated in 12-year cohort of Tehran Thyroid Study (TTS).

METHODS

Reproductive age women(n = 775) without any thyroid disease or ovarian dysfunction were selected from the Tehran Thyroid Study cohort. Participants were divided into four age specific AMH quartiles (Q1-Q4), Q1, the lowest and Q4, the highest. AMH was measured at the initiation of study and thyroid stimulating hormone (TSH), free T4 (FT4), and TPO Ab were measured at baseline and at three follow up visits.

RESULTS

At baseline, there was no statistically significant difference in thyroid hormones between women of the four quartiles, although TPO Ab levels were higher in women of Q1. During the follow ups, FT4 was decreased in all quartiles (p < 0.05), whereas TPO Ab increased in Q1 (p = 0.02). Odds ratio of overall TPO Ab positivity in women of Q1 was 2.08 fold higher than those in Q4. (OR: 2.08, 95%CI: 1.16, 3.72; p = 0.01).

CONCLUSION

Women with the lowest ovarian reserves had higher levels of TPO Ab, with a positive trend of this antibody overtime in comparison to other quartiles, indicating that this group may be at a higher risk of hypothyroidism over time.

Age and Assay Related Changes of Laboratory Thyroid Function Tests in the Reference Female Population

Background

Laboratory thyroid function tests play a central role in the diagnosis of thyroid disorders. The aim of our cross-sectional study was to determine reference values for thyroid tests in a rigorously selected group of Montenegrin females, investigate the impact of possible age-related changes and the influence of the interassay bias between three frequently used immunoassays.

Methods

Female subjects were randomly selected, aged between 20 and 69 and 946 of them met the selection criteria. TSH, fT3, fT4, thyroid peroxidase and thyroglobulin antibodies were measured. Eighty samples were further analyzed on two other immunochemistry platforms.

Results

Median TSH progressively increased with age, there was no difference in fT3, while fT4 was significantly higher in the two oldest groups compared to the others. When using the age-related 97.5 percentile of TSH the percentage of reclassification was highest in the 20-29 years of age group (5.2%, p<0.05). In the oldest band, 7.7% had TSH values above cohort-specific and below the age-related upper reference limit. Bland-Altman bias plots revealed the highest interassay absolute mean difference between compared TSH assays of 24.5% and for fT4 assays of 13.8%.

Conclusions

The correlation coefficients between fT3 assays from different manufacturers were low. Serum TSH and fT4 concentrations increased with age and the implementation of age-specific TSH reference intervals would be of interest. The bias between the three commercial immunoassays indicated that the standardization of thyroid function tests is a task of great importance.

Hypothyroidism in the older population

BACKGROUND

Both overt hypothyroidism as well as minor elevations of serum thyrotropin (TSH) levels associated with thyroid hormones within their respective reference ranges (termed subclinical hypothyroidism) are relatively common in older individuals. There is growing evidence that treatment of subclinical hypothyroidism may not be beneficial, particularly in an older person. These findings are relevant at a time when treatment with thyroid hormones is increasing and more than 10-15% of people aged over 80 years are prescribed levothyroxine replacement therapy.

MAIN BODY

The prevalence of hypothyroidism increases with age. However, the reference range for TSH also rises with age, as the population distribution of TSH concentration progressively rises with age. Furthermore, there is evidence to suggest that minor TSH elevations are not associated with important outcomes such as impaired quality of life, symptoms, cognition, cardiovascular events and mortality in older individuals. There is also evidence that treatment of mild subclinical hypothyroidism may not benefit quality of life and/or symptoms in older people. It is unknown whether treatment targets should be reset depending on the age of the patient. It is likely that some older patients with non-specific symptoms and incidental mild subclinical hypothyroidism may be treated with thyroid hormones and could potentially be harmed as a result. This article reviews the current literature pertaining to hypothyroidism with a special emphasis on the older individual and assesses the risk/benefit impact of contemporary management on outcomes in this age group.

CONCLUSIONS

Current evidence suggests that threshold for treating mild subclinical hypothyroidism in older people should be high. It is reasonable to aim for a higher TSH target in treated older hypothyroid patients as their thyroid hormone requirements may be lower. In addition, age-appropriate TSH reference ranges should be considered in the diagnostic pathway of identifying individuals at risk of developing hypothyroidism. Appropriately designed and powered randomised controlled trials are required to confirm risk/benefit of treatment of subclinical hypothyroidism in older people. Until the results of such RCTs are available to guide clinical management international guidelines should be followed that advocate a conservative policy in the management of mild subclinical hypothyroidism in older individuals.

Indirect Reference Intervals: Harnessing the Power of Stored Laboratory Data

Reference intervals are relied upon by clinicians when interpreting their patients' test results. Therefore, laboratorians directly contribute to patient care when they report accurate reference intervals. The traditional approach to establishing reference intervals is to perform a study on healthy volunteers. However, the practical aspects of the staff time and cost required to perform these studies make this approach difficult for clinical laboratories to routinely use. Indirect methods for deriving reference intervals, which utilise patient results stored in the laboratory's database, provide an alternative approach that is quick and inexpensive to perform. Additionally, because large amounts of patient data can be used, the approach can provide more detailed reference interval information when multiple partitions are required, such as with different age-groups. However, if the indirect approach is to be used to derive accurate reference intervals, several considerations need to be addressed. The laboratorian must assess whether the assay and patient population were stable over the study period, whether data 'clean-up' steps should be used prior to data analysis and, often, how the distribution of values from healthy individuals should be modelled. The assumptions and potential pitfalls of the particular indirect technique chosen for data analysis also need to be considered. A comprehensive understanding of all aspects of the indirect approach to establishing reference intervals allows the laboratorian to harness the power of the data stored in their laboratory database and ensure the reference intervals they report are accurate.

Laboratory Testing in Thyroid Conditions - Pitfalls and Clinical Utility

Thyroid disorders are common, affecting more than 10% of people in the US, and laboratory tests are integral in the management of these conditions. The repertoire of thyroid tests includes blood tests for thyroid-stimulating hormone (TSH), free thyroxine, free triiodothyronine, thyroglobulin (Tg), thyroglobulin antibodies (Tg-Ab), thyroid peroxidase antibodies (TPO-Ab), TSH receptor antibodies (TRAb), and calcitonin. TSH and free thyroid hormone tests are frequently used to assess the functional status of the thyroid. TPO-Ab and TRAb tests are used to diagnose Hashimoto's thyroiditis and Graves' disease, respectively. Tg and calcitonin are important tumor markers used in the management of differentiated thyroid carcinoma and medullary thyroid carcinoma (MTC), respectively. Procalcitonin may replace calcitonin as a biomarker for MTC. Apart from understanding normal thyroid physiology, it is important to be familiar with the possible pitfalls and caveats in the use of these tests so that they can be interpreted properly and accurately. When results are discordant, clinicians and laboratorians should be mindful of possible assay interferences and/or the effects of concurrent medications. In addition, thyroid function may appear abnormal in the absence of actual thyroid dysfunction during pregnancy and in critical illness. Hence, it is important to consider the clinical context when interpreting results. This review aims to describe the above-mentioned blood tests used in the diagnosis and management of thyroid disorders, as well as the pitfalls in their interpretation. With due knowledge and care, clinicians and laboratorians will be able to fully appreciate the clinical utility of these important laboratory tests.

An Age-Specific Serum Thyrotropin Reference Range for the Diagnosis of Thyroid Diseases in Older Adults: A Cross-Sectional Survey in China

Background: The fact that serum thyrotropin (TSH) levels increase with age may influence the diagnosis of thyroid diseases in older adults. This study aimed to establish an age-specific serum TSH reference range, examine the prevalence of thyroid diseases in older adults ≥65 years, and analyze the risk factors. Methods: A cross-sectional study of adult populations in 10 cities in China was conducted from 2010 to 2011. A total of 15,008 subjects were randomly selected and completed the present study. Urinary iodine concentration, serum TSH, thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) titers were measured. Thyroid ultrasonography and questionnaires were completed by all the subjects. When the TSH level was abnormal, free thyroxine and/or free triiodothyronine levels were measured. Results: When the reference range of the general population was used, the prevalence rates of overt hypothyroidism (Ohypo) and subclinical hypothyroidism (Shypo) in older adults ≥65 years were significantly higher than those in younger adults <65 years (2.09% vs. 0.80% and 19.87% vs. 16.23%, respectively; p < 0.001). Positive TPOAb and positive TgAb were associated with the prevalence of Shypo in older adults. An age-specific serum TSH reference range was formulated according to guidelines set forth by the National Academy of Clinical Biochemistry. Both the median and upper limit values of serum TSH in older adults were higher than those in younger adults (2.58 [0.75-8.86] mIU/L vs. 2.38 [0.76-6.57] mIU/L; p < 0.001). Using the age-specific serum TSH reference range, the prevalence of Shypo in older adults was 3.3%, which was significantly lower than the prevalence based on the reference range of the general population (3.3% vs. 19.87%). The prevalence rates of Ohypo, overt hyperthyroidism (Ohyper), and subclinical hyperthyroidism (Shyper) did not change much (Ohypo: 1.6% vs. 2.09%; Ohyper: 0.7% vs. 0.52%; and Shyper: 3.8% vs. 0.73%). Positive TPOAb, but not positive TgAb, was also associated with the prevalence of Shypo as diagnosed with the age-specific serum TSH reference range. Conclusion: The serum TSH level increases with age, which may represent a normal compensatory phenomenon in older adults ≥65 years. To prevent misdiagnosis and mistreatment, the use of an age-specific serum TSH reference range is recommended in older adults for the diagnosis of thyroid diseases.

Age-related change in thyroid-stimulating hormone: a cross-sectional study in healthy euthyroid population

This cross-sectional study aimed to examine changes in thyroid-stimulating hormone (TSH) concentration over age in China and investigate relationship between TSH and risk factors for cardiovascular disease (CVD) among euthyroid subjects. TSH, free triiodothyronine (FT3), free thyroxine (FT4), blood lipid, and glucose were measured. 7,693 individuals were subdivided into different age groups. Associations between TSH and CVD risk factors [age, body mass index (BMI), systolic and diastolic blood pressure, total cholesterol (TC), triglycerides, low density lipoprotein-cholesterol (LDL-C) and high density lipoprotein-cholesterol (HDL-C) and fasting plasma glucose (FPG)] were evaluated with Pearson correlation analysis. Results showed that 2.5th percentile for TSH was consistent across age groups, whereas 97.5th percentile increased in subjects older than 40 years with upper limit being 6.83 mIU/L in subjects aged 60-69 years and 8.07 mIU/L in those older than 70 years. The age-specific upper limits reclassification rate was higher in all age bands as compared to the common cut-off value. TSH was positively associated with age, SBP, DBP, TC and LDL-C and negatively with FT3 and FT4. Serum TSH within new reference range had a linear correlation with SBP, TC and LDL-C in subjects aged <60 years. There were no significant differences in BMI, blood pressure, lipid profile or FPG among subjects 60-69 and older than or equal to 70 years. Elevated TSH within new reference range is associated with risk factors for CVD in subjects aged <60 years. Thus, there might be age-related difference in the relationship between CVD risk factors and elevated serum TSH.

Reference intervals for neonatal thyroid function tests in the first 7 days of life

BACKGROUND

Prompt intervention can prevent permanent adverse neurological effects caused by neonatal hypothyroidism. Thyroid function changes rapidly in the first few days of life but well-defined age-specific reference intervals (RIs) for thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free tri-iodothyronine (FT3) are not available to aid interpretation. We developed hour-based RIs using data mining.

METHODS

All TSH, FT4 and FT3 results with date and time of collection from neonates aged <7 days during 2005-2015 were extracted from the Monash Pathology database. Neonates with more than one episode of testing or with known primary hypothyroidism, identified by treating physicians or from medical records, were excluded from the analysis. The date and time of birth were obtained from the medical records.

RESULTS

Of the 728 neonates qualifying for the study, 569 had time of birth available. All 569 had TSH, 415 had FT4 and 146 had FT3 results. For age ≤24 h, 25-48 h, 49-72 h, 73-96 h, 97-120 h, 121-144 h and 145-168 h of life, the TSH RIs (2.5th-97.5th) (mIU/L) were 4.1-40.2, 3.2-29.6, 2.6-17.3, 2.2-14.7, 1.8-14.2, 1.4-12.7 and 1.0-8.3, respectively; the FT4 RIs (mean ± 2 standard deviation [SD]) (pmol/L) were 15.3-43.6, 14.7-53.2, 16.5-45.5, 17.8-39.4, 15.3-32.1, 14.5-32.6 and 13.9-30.9, respectively; the FT3 RIs (mean±2 SD) (pmol/L) were 5.0-9.4, 4.1-9.1, 2.8-7.8, 2.9-7.8, 3.5-7.2, 3.4-8.0 and 3.8-7.9, respectively.

CONCLUSIONS

TSH and FT4 were substantially high in the first 24 h after birth followed by a rapid decline over the subsequent 168 h. Use of hour-based RIs in newborns allows for more accurate identification of neonates who are at risk of hypothyroidism.

The Relation Between Thyroid Function and Anemia: A Pooled Analysis of Individual Participant Data

Context

Anemia and thyroid dysfunction often co-occur, and both increase with age. Human data on relationships between thyroid disease and anemia are scarce.

Objective

To investigate the cross-sectional and longitudinal associations between clinical thyroid status and anemia.

Design

Individual participant data meta-analysis.

Setting

Sixteen cohorts participating in the Thyroid Studies Collaboration (n = 42,162).

Main Outcome Measures

Primary outcome measure was anemia (hemoglobin <130 g/L in men and <120 g/L in women).

Results

Cross-sectionally, participants with abnormal thyroid status had an increased risk of having anemia compared with euthyroid participants [overt hypothyroidism, pooled OR 1.84 (95% CI 1.35 to 2.50), subclinical hypothyroidism 1.21 (1.02 to 1.43), subclinical hyperthyroidism 1.27 (1.03 to 1.57), and overt hyperthyroidism 1.69 (1.00 to 2.87)]. Hemoglobin levels were lower in all groups compared with participants with euthyroidism. In the longitudinal analyses (n = 25,466 from 14 cohorts), the pooled hazard ratio for the risk of development of anemia was 1.38 (95% CI 0.86 to 2.20) for overt hypothyroidism, 1.18 (1.00 to 1.38) for subclinical hypothyroidism, 1.15 (0.94 to 1.42) for subclinical hyperthyroidism, and 1.47 (0.91 to 2.38) for overt hyperthyroidism. Sensitivity analyses excluding thyroid medication or high levels of C-reactive protein yielded similar results. No differences in mean annual change in hemoglobin levels were observed between the thyroid hormone status groups.

Conclusion

Higher odds of having anemia were observed in participants with both hypothyroid function and hyperthyroid function. In addition, reduced thyroid function at baseline showed a trend of increased risk of developing anemia during follow-up. It remains to be assessed in a randomized controlled trial whether treatment is effective in reducing anemia.

Clinical aspects of thyroid function during ageing

Globally, populations are ageing at a rapid rate. The increase in the number of older citizens is accompanied by an increased prevalence of thyroid dysfunction, one of the most common disorders in older people. However, the diagnosis of thyroid dysfunction in older people is hindered by several factors, including the scarcity of thyroid dysfunction symptoms in older people. We describe the physiological changes in thyroid function that occur with increasing age, focusing on literature regarding changes in thyroid function test results in older populations. We also discuss treatment considerations for clinical and subclinical thyroid dysfunction according to international guidelines for older people. Finally, we discuss the relationship between variations in thyroid function and common diseases of old age including cardiovascular disease, osteoporosis, cognitive impairment, and frailty and suggest directions for future research.

Reference intervals for thyrotropin in an area of Northern Italy: the Pordenone thyroid study (TRIPP)

PURPOSE

Thyrotropin (TSH) is the most accurate marker of thyroid dysfunction in the absence of pituitary or hypothalamic disease. Studies on TSH reference intervals (RIs) showed wide inter-individual variability and prompted an intense debate about the best estimation of TSH RIs.

DESIGN

We performed a population study on TSH RIs, using current data stored in the laboratory information system (LIS), at the Hospital Department of Laboratory Medicine, Pordenone (Italy), historically an area of mild-moderate iodine deficiency with a relatively high goiter prevalence.

METHODS

136,650 individuals constituted the final sample. A TSH immunoassay was performed on fasting serum samples with the Dimension Vista 1500 analyzer (Siemens Healthineers). We adopted the Kairisto's procedure to analyze TSH data downloaded by the LIS, applying the indirect strategy for deriving RIs.

RESULTS

TSH RIs of the entire population were 0.32-3.36 mIU/L with a distribution skewed towards higher values. RIs were 0.26-3.61 mIU/L for females, and 0.32-3.01 mIU/L for males. Unlike other studies, TSH median levels progressively decreased from 0-4 to 85-104 years in the overall population, both in male and in female subgroups, showing an inverse correlation between TSH and age in all groups.

CONCLUSIONS

This study is the first to analyze a high percentage (40%) of individuals from an ethnically homogenous Caucasian population. The results obtained emphasize the opportunity to define the TSH RIs according to age, gender and race, in addition to assay methods, and provide further insight about the possible role of iodine status.

High Serum Thyrotropin Concentrations within the Reference Range: A Predictor of Malignancy in Nodular Thyroid Disease

OBJECTIVE

This study assessed whether or not a simple biochemical parameter, serum thyrotropin (TSH), within the reference range can predict the likelihood of thyroid malignancy in subjects undergoing fine-needle aspiration biopsy (FNAB) for thyroid nodules.

SUBJECTS AND METHODS

This cross-sectional study evaluated 236 patients without overt thyroid dysfunction who were not on levothyroxine therapy. They underwent FNAB of the thyroid nodules at the Clementino Fraga Filho University Hospital between 2011 and 2012. The reference range and serum TSH quartiles were determined according to age-specific values for serum TSH and then compared between the cases with benign thyroid nodular disease and differentiated thyroid carcinoma (DTC) based on surgical pathology reports.

RESULTS

Of the 236 patients, 201 (85.1%) underwent a surgical procedure (thyroidectomy) and 89/236 (44.3%) had DTC. The mean TSH concentrations were 2.09 ± 1.15 mU/L in benign patients versus 2.73 ± 1.33 mU/L in cases of DTC (p < 0.01). As TSH increased from quartiles 1 to 4, the frequency of a malignant diagnosis also increased progressively from 22% in quartile 1 to 65% in the last quartile (p ≤ 0.001).

CONCLUSION

Thyrotropin levels were positively associated with the diagnosis of DTC in thyroid nodules.

Childhood Thyroid Function Reference Ranges and Determinants: A Literature Overview and a Prospective Cohort Study

BACKGROUND

Reported cutoffs for childhood thyrotropin (TSH) and free thyroxine (fT4) reference ranges vary widely, and knowledge on the determinants of childhood thyroid function is sparse. This study aimed to summarize the existing studies on thyroid function reference ranges in children. Furthermore, the objective was to investigate the determinants of childhood TSH and fT4 concentration in a population based-prospective cohort.

METHODS

First, to identify studies on childhood thyroid reference ranges, The National Library of Medicine's PubMed, Embase, Ovid Medline, Web of Science, and Google Scholar databases were systematically searched. Second, in a non-selected sample of 4273 children (median age 6.0 years, range 4.9-9.1 years) from the cohort, the associations of age, sex, anthropometric characteristics, ethnicity, maternal education, and time and season at venipuncture were studied with TSH and fT4 concentrations. The study also investigated to what extent between-individual variations in the determinants of TSH and fT4 could influence the calculation of reference ranges.

RESULTS

Published reference ranges for TSH and fT4 differ per age range and within age ranges (cutoffs low TSH: 0.13 to >1 mIU/L; high TSH: 2.36 to >10 mIU/L; low fT4: 7.0 to >10 pmol/L; high fT4: 15.5 to >30 pmol/L). In the present cohort, weight, sex, and ethnicity were determinants of TSH (p ≤ 0.03) and fT4 concentrations (p ≤ 0.01), and height and time at venipuncture were determinants of TSH only (p < 0.0001). The between-individual variation depending on clinical determinants for TSH ranged between 0.64 and 0.96 mIU/L (total population 0.87 mIU/L) for the lower limit and 4.30 and 5.62 mIU/L (total population 5.20 mIU/L) for the upper limit, whereas for fT4, the lower limit ranged between 13.6 and 14.2 pmol/L (total population 13.8 pmol/L) and the upper limit ranged between 20.2 and 23.0 pmol/L (total population 20.8 pmol/L).

CONCLUSIONS

Considerable differences exist in the reported reference ranges for childhood TSH and fT4 across and within age ranges and assays. The present cohort shows only a minimal association between TSH and fT4, suggesting that the hypothalamus-pituitary-thyroid axis remains unaffected by thyroid interfering factors. Various determinants of TSH and fT4 in children were identified, which accounted for a considerable variation of reference range cutoffs.

Rationalizing Thyroid Function Testing: Which TSH Cutoffs Are Optimal for Testing Free T4?

CONTEXT

Thyroid function testing often uses thyrotropin (TSH) measurement first, followed by reflex testing for free thyroxine (T4) if TSH is outside the reference range. The utility of different TSH cutoffs for reflex testing is unknown.

OBJECTIVE

To examine different TSH cutoffs for reflex free T4 testing.

DESIGN, SETTING, AND PATIENTS

We analyzed concurrent TSH and free T4 results from 120,403 individuals from a single laboratory in Western Australia (clinical cohort) and 4568 Busselton Health Study participants (community cohort).

RESULTS

In the clinical cohort, restricting free T4 measurement to individuals with TSH <0.3 or >5.0 mU/L resulted in a 22% reduction in free T4 testing compared with a TSH reference range of 0.4 to 4.0 mU/L; using TSH cutoffs of 0.2 and 6.0 mU/L resulted in a 34% reduction in free T4 testing. In the community cohort, the corresponding effect was less: 3.3% and 4.8% reduction in free T4 testing. In the clinical cohort, using TSH cutoffs of 0.2 and 6.0 mU/L, elevated free T4 would go undetected in 4.2% of individuals with TSH levels of 0.2 to 0.4 mU/L. In most, free T4 was marginally elevated and unlikely to indicate clinically relevant hyperthyroidism. Low free T4 would go undetected in 2.5% of individuals with TSH levels of 4 to 6 mU/L; in 94%, free T4 was marginally reduced and unlikely to indicate clinically relevant hypothyroidism.

CONCLUSIONS

Setting TSH cutoffs at 0.1 to 0.2 mU/L less than and 1 to 2 mU/L greater than the reference range for reflex testing of free T4 would reduce the need for free T4 testing, with minimal effect on case finding.

Hypothyroidism

Hypothyroidism is a common condition of thyroid hormone deficiency, which is readily diagnosed and managed but potentially fatal in severe cases if untreated. The definition of hypothyroidism is based on statistical reference ranges of the relevant biochemical parameters and is increasingly a matter of debate. Clinical manifestations of hypothyroidism range from life threatening to no signs or symptoms. The most common symptoms in adults are fatigue, lethargy, cold intolerance, weight gain, constipation, change in voice, and dry skin, but clinical presentation can differ with age and sex, among other factors. The standard treatment is thyroid hormone replacement therapy with levothyroxine. However, a substantial proportion of patients who reach biochemical treatment targets have persistent complaints. In this Seminar, we discuss the epidemiology, causes, and symptoms of hypothyroidism; summarise evidence on diagnosis, long-term risk, treatment, and management; and highlight future directions for research.

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.

TSH-independent release of thyroid hormones through cold exposure in aging rats

Thyroid function decreases and cold exposure response becomes impaired with increasing age. We investigated the age-related changes in thyroid structure and function and cold-induced changes in the thyroid activity of aging rats. Thirty-two male Sprague–Dawley rats were randomly divided into four groups (8 rats per group): young (7 months) and old (22 months) groups exposed to room temperature and cold stress. The active follicle ratio and serum free T3, T4 and TSH, and TSH receptor (TSHR) concentrations in the thyroid tissues of the rats from each group were compared. At room temperature, old rats had significantly lower active follicle ratio and free T3 and T4 concentrations than young rats. Furthermore, old rats displayed higher TSH level than young. Exposure to cold temperature led to significantly increased active colloid ratio and free T3 and T4 concentrations among old rats, but no significant differences were found among young rats. Additionally, no significant changes in the TSH and TSHR levels were observed after cold exposure in both young and old rats. Old rats have lower thyroid function than young rats under normal temperature. Aging rats are more susceptible to cold stress than young rats, and cold-induced thyroid activation occurs independently of TSH.

We investigated the age-related changes in the thyroid structure and function and cold-induced changes in the thyroid activity of aging rats. Aging rats have structurally less active thyroid follicles and functionally lower thyroid hormone levels than young rats. Furthermore, old rats are more susceptible to cold stress than young rats, and cold-induced thyroid activation occurs independently of TSH.

Reference intervals for thyroid hormones on Advia Centaur derived from three reference populations and a review of the literature

INTRODUCTION

Laboratories are recommended to determine their own local reference intervals (RIs) to embrace the variations in local populations. We have assessed local RIs for thyroid function tests using two different approaches to selection of reference populations and also searched the literature for studies using the Advia Centaur methods.

METHODS

Two independent populations were made of redundant serum samples from primary care in which exclusion criteria were used to reduce the inclusion of patients with thyroid disease. A further population of healthy subjects were recruited. All groups were restricted to 18-65 years and thyroid peroxidase antibodies (TPOabs) positive subjects were excluded. All samples were analysed using Advia Centaur reagents. A literature search was made for RI studies on non-pregnant adults using Advia Centaur.

RESULTS

Redundant data sets consisted of 219 and 222 subjects and a healthy population of 280. Comparison of variance of all three groups showed differences for free T4 (fT4) and total T3 (TT3) (analysis of variance P < 0.0001) but thyroid-stimulating hormone (TSH) was similar across all three groups (P = 0.7656). RI for TSH, fT4 and TT3 all fell within the 95% confidence interval for each other for all three analytes. Published RIs give wide variation although their mean is similar to the prospective data reported here.

DISCUSSION

Our data suggest that a consensus set of RIs for Advia Centaur can be adopted from the prospective studies and literature search in this paper and we would suggest the following RIs: TSH 0.5-4.4 mIU/L; fT4 10-20 pmol/L; and TT3 1.1-2.4 nmol/L.

A Preliminary Link between Hydroxylated Metabolites of Polychlorinated Biphenyls and Free Thyroxin in Humans

BACKGROUND

Polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (HO-PCBs) interfere with thyroid hormone action both in vitro and in vivo. However, epidemiologic studies on the link between PCB exposure and thyroid function have yielded discordant results, while very few data are available for HO-PCBs.

OBJECTIVES

Our study aimed at investigating the relationship between clinically available markers of thyroid metabolism and serum levels of both PCBs and HO-PCBs.

SUBJECTS AND METHODS

In a group of 180 subjects, thyroid-stimulating hormone (TSH) and free thyroxin (fT4), 29 PCBs (expressed both in lipid weight and in wet weight) and 18 HO-PCBs were measured in serum.

RESULTS

In regression models, adjusted for gender, age, current smoking behavior, BMI and total lipid levels, serum levels of 3HO-PCB118 and 3HO-PCB180, and PCB95(lw), PCB99(lw) and PCB149(lw) were independent, significant predictors of fT4. A stepwise, multiple regression with gender, age, current smoking behavior, BMI and total lipid levels and all five previously identified significant compounds retained age, BMI, PCB95(lw), PCB99(lw) and 3HO-PCB180 as significant predictors of fT4. TSH levels were not predicted by serum levels of any of the PCBs or HO-PCBs.

CONCLUSIONS

Our study indicates that in vivo, circulating fT4 levels can be linked to serum levels of several PCBs and hydroxylated PCB metabolites.

High Frequency of Thyroid Disorders in Patients Presenting With Neutropenia to an Outpatient Hematology Clinic STROBE-Compliant Article

Granulopoiesis abnormalities have been described in association with thyroid disorders (TD). However, data regarding systematic evaluation of adult neutropenia and concurrent or prior TD are scarce. To investigate the frequency of TD among patients presenting with neutropenia, and the immunophenotypic and immunologic profile of neutropenic patients with concomitant thyroidopathy. Two hundred eighteen consecutive neutropenic patients were prospectively evaluated in our outpatient Hematology Clinic, with a detailed laboratory screen, including thyroid function tests, antineutrophil antibodies, blood lymphocytes immunophenotyping, and detection of T-cell clonality by PCR. Among 218 patients with neutropenia, 95 (43.6%) had TD, 65 chronic immunologic neutropenia, 20 clonal proliferation of T-large granular lymphocytes (T-LGL), 5 autoimmune disorders, and 33 other diagnoses. TD-patients had an increased frequency of recurrent infections compared with other patients (P = 0.045). The following correlations were found: negative correlation between FT3 and absolute neutrophil count (ANC) (r² = -0.274, P = 0.007), negative correlation between TPO-Abs/TG-Abs and C4 (r² = -0.16, P = 0.045; r² = -0.266, P = 0.001), and CD4⁺ counts were inversely correlated to T4 and positively to TSH (r² = -0.274, P = 0.024; r² = 0.16, P = 0.045). In addition, TD-patients had significantly higher percentages of CD4⁺ lymphocytes (P = 0.003). Among TD-patients, 23.4% had Hashimoto thyroiditis (HT), 4.1%, Graves disease (GD), 8.2% nontoxic multinodular goiter (NTMG), 5% subclinical hypothyroidism, and 2.8% had undergone total thyroidectomy associated with nodules (TTM). Thirteen TD-patients displayed T-LGL. Patients with autoimmune thyroidopathy had an increased frequency of concomitant autoimmune manifestations (P = 0.03). Significant differences between the different thyroidopathies included: HT-patients had higher percentages of B-lymphocytes, while the opposite was evident for the TTM-subgroup (P = 0.009, 0.02); GD-patients showed an increase of the proportion of NK cells and a decrease in the percentage of TCRγδ+ lymphocytes (P = 0.001, 0.045); and NTMG-patients had significantly higher ANC (P = 0.004) compared to other thyroidopathies. Antineutrophil antibodies were found in 37.2% of TD-patients tested. Anti-TPO titers were significantly higher in patients with positive antineutrophil antibodies (P = 0.04). The frequency of TD among neutropenic patients may be higher than previously reported. The existence of antineutrophil antibodies, as well as the different distribution of lymphocyte subsets among patients with different TD, suggests both humoral and cellular mechanisms in the pathophysiology of thyroid disease-associated neutropenia.

Subclinical Hypothyroidism and the Risk of Stroke Events and Fatal Stroke: An Individual Participant Data Analysis

OBJECTIVE

The objective was to determine the risk of stroke associated with subclinical hypothyroidism.

DATA SOURCES AND STUDY SELECTION

Published prospective cohort studies were identified through a systematic search through November 2013 without restrictions in several databases. Unpublished studies were identified through the Thyroid Studies Collaboration. We collected individual participant data on thyroid function and stroke outcome. Euthyroidism was defined as TSH levels of 0.45-4.49 mIU/L, and subclinical hypothyroidism was defined as TSH levels of 4.5-19.9 mIU/L with normal T4 levels.

DATA EXTRACTION AND SYNTHESIS

We collected individual participant data on 47 573 adults (3451 subclinical hypothyroidism) from 17 cohorts and followed up from 1972-2014 (489 192 person-years). Age- and sex-adjusted pooled hazard ratios (HRs) for participants with subclinical hypothyroidism compared to euthyroidism were 1.05 (95% confidence interval [CI], 0.91-1.21) for stroke events (combined fatal and nonfatal stroke) and 1.07 (95% CI, 0.80-1.42) for fatal stroke. Stratified by age, the HR for stroke events was 3.32 (95% CI, 1.25-8.80) for individuals aged 18-49 years. There was an increased risk of fatal stroke in the age groups 18-49 and 50-64 years, with a HR of 4.22 (95% CI, 1.08-16.55) and 2.86 (95% CI, 1.31-6.26), respectively (p trend 0.04). We found no increased risk for those 65-79 years old (HR, 1.00; 95% CI, 0.86-1.18) or ≥ 80 years old (HR, 1.31; 95% CI, 0.79-2.18). There was a pattern of increased risk of fatal stroke with higher TSH concentrations.

CONCLUSIONS

Although no overall effect of subclinical hypothyroidism on stroke could be demonstrated, an increased risk in subjects younger than 65 years and those with higher TSH concentrations was observed.

Paediatric reference interval and biological variation trends of thyrotropin (TSH) and free thyroxine (T4) in an Asian population

AIMS

To describe the reference intervals and biological variation data for thyrotropin (TSH) and free thyroxine (FT4) in a mixed Asian population using an indirect sampling approach and to compare them with published reports.

METHODS

TSH and FT4 of children measured once or twice over a 7-year period (2008-2014) at primary-care and tertiary-care settings were extracted from the laboratory information system. After excluding outliers, age-related reference intervals were derived using the Lambda-Mu-Sigma (LMS) approach, while age-partitioned biological variation data were obtained according to recommendations by Fraser and Harris.

RESULTS

Both TSH and FT4 were very high at birth and declined with age. Similarly within-individual and between-individual biological variations were higher for both TSH and FT4 at birth and also declined with age. Our data were broadly similar to previous studies. Significant heterogeneity in study population and methods prohibited direct numerical comparison between this and previously published studies.

CONCLUSIONS

This study fills two important gaps in our knowledge of paediatric thyroid function by reporting the centile trends (and reference values) in a mixed Asian population, as well as providing age-partitioned biological variation data. The variation in published reference intervals highlights the difficulty in harmonising paediatric thyroid reference intervals or recommending universal clinical cut-offs.

Subclinical hypothyroidism in children and adolescents: is it clinically relevant?

Although subclinical hypothyroidism (SH) is a common clinical problem, its diagnosis tends to be incidental. According to the definition, it should be asymptomatic, only detectable by screening. The presence or coincidence of any symptoms leads to L-thyroxine treatment. The clinical presentation, especially in younger patients with subclinical hypothyroidism, is still under dispute. Accordingly, the aim of this paper was to review the literature from the past seven years. The literature search identified 1,594 potentially relevant articles, of which 24 met the inclusion criteria. Few studies focus on the symptomatology of subclinical hypothyroidism, and most of them analyzed a small number of subjects. A significant correlation was found by some authors between subclinical hypothyroidism and a higher risk of hypertension, dyslipidemia, and migraine. No evidence of the impact of subclinical hypothyroidism on weight, growth velocity, and puberty was revealed. As the quality of most studies is poor and no definite conclusions can be drawn, randomized, large-scale studies in children and adolescents are warranted to determine the best care for patients with SH.