Thyroid Stimulating Hormone and Thyroid Hormones (Triiodothyronine and Thyroxine): An American Thyroid Association-Commissioned Review of Current Clinical and Laboratory Status

Evaluating cardiac electrophysiological markers for predicting arrhythmic risk in hypothyroid patients

OBJECTIVES

This study aimed to evaluate the impact of hypothyroidism and levothyroxine (LT4) treatment on arrhythmic risk by concurrently analyzing multiple electrocardiogram (ECG) parameters such as the Index of Cardio-Electrophysiological Balance (iCEB), frontal QRS-T angle, Tpeak-Tend (Tp-e) interval/QT interval ratio, and QT dispersion (QTd).

METHODS

This cross-sectional study included 132 adult patients with primary hypothyroidism who had been receiving LT4 treatment, and 132 demographically matched healthy controls. The hypothyroid group was also stratified by thyroid-stimulating hormone (TSH) levels (subclinical <4.5 and overt ≥ 4.5). Participants underwent a series of thyroid function and ECG measurements.

RESULTS

The hypothyroid and healthy control groups were matched for age and gender (p = 0.080; p = 0.176). Participants with hypothyroidism had higher Tp-e/QT ratios, iCEB, median frontal QRS-T angle, and corrected QT dispersion (cQTd) than healthy controls (p = 0.004; p = 0.025; p = 0.004; p = 0.004, respectively). In the overt group, the Tp-e/QT ratio, iCEB, and median frontal QRS-T angles were all higher (p = 0.012, p = 0.037, and p = 0.016, respectively). Logistic regression analysis indicated that a higher iCEB score (β = 0.60, p = 0.003) was significant for the detection of arrhythmia risk. ROC analysis showed that iCEB had the highest sensitivity (0.80), moderate specificity (0.60), and AUC 0.70.

CONCLUSION

Patients with hypothyroidism have a higher risk of arrhythmia. To assess this risk, it is important to analyze the Tp-e interval, iCEB, frontal QRS-T angle, and QTd. Differentiating between patients with subclinical and overt hypothyroidism can help minimize the risk of arrhythmia. iCEB is the most effective method for identifying arrhythmic risk. Using all these parameters can improve the accuracy of arrhythmic risk detection in patients with hypothyroidism.

Defining Gestational Thyroid Dysfunction Through Modified Nonpregnancy Reference Intervals: An Individual Participant Meta-analysis

BACKGROUND

Establishing local trimester-specific reference intervals for gestational TSH and free T4 (FT4) is often not feasible, necessitating alternative strategies. We aimed to systematically quantify the diagnostic performance of standardized modifications of center-specific nonpregnancy reference intervals as compared to trimester-specific reference intervals.

METHODS

We included prospective cohorts participating in the Consortium on Thyroid and Pregnancy. After relevant exclusions, reference intervals were calculated per cohort in thyroperoxidase antibody-negative women. Modifications to the nonpregnancy reference intervals included an absolute modification (per .1 mU/L TSH or 1 pmol/L free T4), relative modification (in steps of 5%) and fixed limits (upper TSH limit between 3.0 and 4.5 mU/L and lower FT4 limit 5-15 pmol/L). We compared (sub)clinical hypothyroidism prevalence, sensitivity, and positive predictive value (PPV) of these methodologies with population-based trimester-specific reference intervals.

RESULTS

The final study population comprised 52 496 participants in 18 cohorts. Optimal modifications of standard reference intervals to diagnose gestational overt hypothyroidism were -5% for the upper limit of TSH and +5% for the lower limit of FT4 (sensitivity, .70, CI, 0.47-0.86; PPV, 0.64, CI, 0.54-0.74). For subclinical hypothyroidism, these were -20% for the upper limit of TSH and -15% for the lower limit of FT4 (sensitivity, 0.91; CI, 0.67-0.98; PPV, 0.71, CI, 0.58-0.80). Absolute and fixed modifications yielded similar results. CIs were wide, limiting generalizability.

CONCLUSION

We could not identify modifications of nonpregnancy TSH and FT4 reference intervals that would enable centers to adequately approximate trimester-specific reference intervals. Future efforts should be turned toward studying the meaningfulness of trimester-specific reference intervals and risk-based decision limits.

Blood levels of zearalenone, thyroid-stimulating hormone, and thyroid hormones in patients with colorectal cancer

Mycotoxins are secondary metabolites produced by various species of mold fungi commonly found in plant materials. Zearalenone (ZEN) adversely affects the endocrine system. This study aimed to determine whether thyroid-stimulating hormone (TSH), procalcitonin (PCT), free triiodothyronine (fT3), and free thyroxine (fT4) levels are altered during natural zearalenone mycotoxicosis in patients diagnosed with sigmoid colon cancer (SCC) or colorectal cancer (CRC). A study was conducted on women and men diagnosed with SCC or CRC accompanied by the presence or absence (Patients Without ZEN - PWZ group) of ZEN in the blood. The PWZ group consisted of 17 patients with symptoms of SCC and CRC in whom ZEN and its metabolites were not detected in peripheral blood. The experimental (empirical) groups included a total of 16 SCC and CRC patients who tested positive for ZEN, but not its metabolites. TSH values in both sexes were within the upper limit of the reference range (0.27 - 4.2 μIU/mL) adopted by the hospital laboratory and corresponded to the upper second tertile and the lower third tertile. PCT values demonstrated that SCC and CRC were accompanied by a systemic or local bacterial infection. All mean values of fT3 were in the middle of the reference range, and the mean values of fT4 were within the upper reference limit. The fT3/fT4 prognostic marker was somewhat above the cut-off point of 0.22. These results indicate that in postmenopausal women and andropausal men who were diagnosed with SCC and CRC and were exposed to food-borne ZEN, higher values of the prognostic marker (fT3/fT4) were associated with an unfavorable prognosis. The study also revealed that the more distal the neoplastic lesions in the colon, the higher the percentage of both thyroid hormones, regardless of the patient's sex. The presence of ZEN in the diet alters thyroid activity in patients diagnosed with SCC and CRC.

Association between air pollutants, thyroid disorders, and thyroid hormone levels: a scoping review of epidemiological evidence

Background

Over the past two decades, the incidence of thyroid disorders has been steadily increasing. There is evidence to suggest that air pollution may be one of the etiological factors of thyroid diseases. This comprehensive review aimed to examine the evidence related to air pollutants and thyroid disorders and thyroid hormones levels from an epidemiological perspective.

Methods

The scoping review adopted a systematic approach to search for, identify, and include peer-reviewed articles published in English. We performed a comprehensive search of three databases-PubMed, Embase, and Web of Science to identify relevant literature on the relationship between air pollution [particulate matter, nitrogen oxide, carbon monoxide (CO), ozone (O3), sulfur dioxide (SO2)] exposure and thyroid disorders, including hypothyroidism, congenital hypothyroidism (CH), thyroid nodules, thyroid cancer, autoimmune thyroid diseases, as well as thyroid hormone levels, such as thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4). Articles published until August 1, 2023, were included.

Results

A total of 3,373 studies were retrieved, and among them, 25 studies covering eight different air pollutants were relevant. The most frequently studied air pollutants in this review included fine particulate matter (with fine particulate matter (PM2.5), n=21; inhalable particles (PM10), n=10; PM10-2.5, n=1) and nitrogen oxides (with NO2, n=13; NOx, n=3). The thyroid disorders and thyroid hormone levels most commonly associated with evidence of air pollution exposure were hypothyroidism (n=7) and TSH (n=12).

Conclusions

Despite variations in study designs and exposure assessments, the findings consistently highlight the substantial health risks that air pollution, particularly PM2.5, poses to thyroid health, especially among vulnerable populations. Given that our study was limited to epidemiological investigations and the increasing prevalence of toxic substances in the environment, there is an urgent need for further research to elucidate the mechanisms by which these pollutants disrupt thyroid function and contribute to the development of thyroid diseases.

The association between circulating saturated fatty acids and thyroid function: results from the NHANES 2011-2012

Background

Excessive saturated fatty acids (SFAs) are known to be detrimental to human health. Although the majority of research and dietary guidelines have focused on the intake of SFAs, there has been limited attention to the relationship between circulating SFA levels and hormonal regulation, such as that of thyroid hormones.

Methods

To explore potential associations, we conducted an investigation with 579 participants from the National Health and Nutrition Examination Survey (NHANES) 2011-2012. Subgroup analyses and multivariable linear regression models were used to estimate the relationships between eleven distinct SFA concentrations and various thyroid parameters.

Results

For 579 adults, subgroup analysis of thyroid stimulating hormone (TSH) revealed significant differences in nine specific SFAs and the total SFA levels (all p < 0.05). Furthermore, multivariable linear regression analysis identified positive correlations between certain SFAs and various parameters, including TSH, total triiodothyronine (TT3), free triiodothyronine (FT3), thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb), thyroglobulin (Tg), the ratio of FT3 to free thyroxine (FT4) (FT3/FT4), and the thyrotroph T4 resistance index (TT4RI). Conversely, negative correlations were observed between certain SFAs and total thyroxine (TT4), FT4, the ratio of FT3/TT3, and the thyroid feedback quantile-based index (TFQI) (all p < 0.05).

Conclusion

These findings collectively suggest associations between SFAs and thyroid parameters, highlighting the need for future studies to elucidate the underlying mechanisms of these interactions.

Bisphenol A exposure and thyroid dysfunction during pregnancy: A systematic review

Bisphenol A (BPA) is a phenolic chemical that has been found to be associated with human health outcomes. It is one of the risk factors for thyroid function. Pregnancy is a vulnerable window for thyroid problems, because of the fluctuations in hormone levels. This review aimed to evaluate the association between BPA exposure and thyroid function during pregnancy. We conducted a comprehensive search of relevant databases, including PubMed, Scopus, Embase, Web of Science, and the Cochrane Library, for original studies published in English that reported data on BPA levels and thyroid-related hormone levels in pregnant women. We used the Newcastle-Ottawa Scale (NOS) to assess the methodological quality of the studies and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) method to evaluate the quality of evidence. In total, 11 studies involving 6526 individuals were included in this systematic review. These studies explored fluctuations in thyroid-related hormones, including TSH, TT3, TT4, FT3, and FT4 levels, as well as the TT4/TT3 and FT4/FT3 ratios. The systematic review is to evaluate the evidences between bisphenol A exposure and thyroid-related hormones in pregnant women. We found that BPA exposure in pregnancy might disturb the homeostasis of maternal thyroid-related hormones and suggest an increased risk of hyperthyroidism. Further studies based on the findings are required to explore the underlying mechanisms and determine the potential effects of BPA exposure on thyroid function during pregnancy.

Thyroid Hormone Homeostasis in Levothyroxine-treated Patients: Findings From ELSA-Brasil

CONTEXT

The effectiveness of levothyroxine (LT4) in restoring thyroid hormone (TH) homeostasis, particularly serum thyroxine (T4) and triiodothyronine (T3) levels, remains debatable.

OBJECTIVE

This work aimed to assess TH homeostasis in LT4-treated individuals using data from the Longitudinal Study of Adult Health in Brazil (ELSA-Brasil) study.

METHODS

The ELSA-Brasil study follows 15 105 adult Brazilians (aged 35-74 years) over 8.2 years (2008-2019) with 3 observation points assessing health parameters including serum thyrotropin (TSH), free T4 (FT4), and free T3 (FT3) levels. We analyzed 186 participants that initiated treatment with LT4 during the study, and 243 individuals continuously treated with LT4 therapy.

RESULTS

Initiation of therapy with LT4 resulted in an 11% to 19% decrease in TSH, an approximately 19% increase in FT4, and a 7% reduction in FT3 serum levels (FT3 dropped >10% in ∼40% of the LT4-treated patients). This was associated with an increase in triglyceride levels and utilization of hypolipidemic and antidiabetic medications. Participants continuously treated with LT4 exhibited a stable elevation in serum FT4 and a reduction in serum FT3 and TSH levels. While 115 participants (47.3%) had at least 1 serum FT4 levels above the control reference range (>1.52 ng/dL), 38 participants (15.6%) had at least 1 serum FT3 below the reference range (<0.23 ng/dL).

CONCLUSION

The present results challenge the dogma that treatment with LT4 for hypothyroidism restores TH homeostasis in all patients. A substantial number of LT4-treated patients exhibit repeated FT4 and FT3 levels outside the normal reference range, despite normal TSH levels. Further studies are needed to define the clinical implications of these findings.

Oncosexology - selected issues taking into account the problem of sexological care of patients with cancer

As can be seen from research, 44% of oncological problems disclose problems in relationships with a partner. About 80% of oncological patients report deterioration of the quality of their sexual life. Although the situation improves, a significant majority of ill persons do not obtain assistance in the scope of sexuality during oncological treatment. Intimacy is an important sphere of life and can support the process of recovery. Intimacy plays special role in the difficult period of the fight against disease. Independently of the applied method of oncological treatment, side effects of therapy can influence one's sexual life. This means that an increasing number of persons who are healed from cancerous disease are exposed to the long-term undesirable influence of treatment. The process of oncological treatment has an essential impact on the intimate life of those who suffer from oncological diseases. To a great extent, this process and the disease itself contribute to a decrease of the quality of life due to the appearance of symptoms caused by earlier menopause, they negatively influence the feeling desire and sexual performance. Unfortunately, despite the development of oncosexology, sexual problems of oncologically ill persons are not noticed, and sometimes they are played down or overlooked due to everyday problems.

A comparative cross-sectional study on the quality of life in Grave's disease patients: urban vs. rural perspectives

Grave's disease affects numerous patients globally, but its impact on health-related quality of life (HR-QoL) in relation to geographical disparities remains under-explored. This cross-sectional study aimed to assess the influence of urban versus rural residence on HR-QoL among patients diagnosed with Graves' Disease in Rajasthan, India. One hundred seven Graves' disease patients from rural and urban endocrine centers were analyzed. The rural group included 52 patients (24 males, 28 females), averaging 38.9 ± 10.9 years of age, while the urban group had 55 (13 males, 42 females) with an average age of 39.1 ± 14.2 years. We found differences between rural and urban patients in terms of gender ratio, BMI, smoking habits, and obesity. Multivariable linear regression was used in both groups to determine the association between the baseline characteristics of Graves' patients from both areas and HR-QOL. Health-related quality of life, assessed via the SF-36 questionnaire, indicated higher general health and role emotional scores among urban patients. Our study found that the duration of Graves' disease in rural centers negatively impacted physical health scores. In urban patients, age and BMI influenced physical health, while gender and disease duration affected mental health scores in rural patients. Age impacted mental health in urban patients. Rural patients had a poorer quality of life compared to urban patients. Differences in gender distribution, BMI, smoking habits, and obesity rates revealed disparities in Graves' disease between rural and urban patients in India, highlighting the need for better healthcare infrastructure and awareness in rural areas.

Impact of peripheral thyroid hormone balance on liver fat: insights from the NutriAct trial

OBJECTIVE

Hypothyroidism has been proposed as a potential contributor to steatotic liver disease (SLD), but existing data shows conflicting results in euthyroid subjects. Therefore, we investigated the association between thyroid function and intrahepatic lipids (IHLs) during a 36-month randomized controlled trial evaluating a diet known to reduce liver fat.

DESIGN

502 eligible subjects (aged 50-80 years, ≥1 risk factor for unhealthy aging) were randomly assigned to either follow a diet rich in unsaturated fatty acids, plant protein, and fiber (intervention group, IG), or dietary recommendations of the German Nutrition Society (control group, CG).

METHODS

Serum levels of thyroid hormones (THs) as well as IHLs, defined via magnetic resonance spectroscopy, were measured within an euthyroid subgroup without significant alcohol consumption at baseline (n = 332) and after 12 months (n = 243). A ratio of T3/T4 was used to assess whole-body deiodinase activity. Estimates of glucose and lipid metabolism were analyzed.

RESULTS

Only fT3 and T3/T4 ratios showed a significant positive correlation with IHL at baseline. We observed a significant decline in fT3, T3, fT3/fT4 ratio, and T3/T4 ratio in CG and IG after 12 months without significant differences between groups. TSH, fT4, and T4 remained stable. A larger improvement of IHL during dietary intervention was seen in those subjects with a lower decline in T3 concentrations.

CONCLUSIONS

Altered TH balance indicates a possible compensatory upregulation of whole-body TH activity in subjects with increased liver fat. This might be also relevant during the improvement of hepatic steatosis.

Delta check limits for thyroid function tests adjusted for clinical settings

BACKGROUND

This study aimed to determine practical delta check limits (DCLs) for thyroid function tests (TFTs) to detect sample misidentifications across various clinical settings.

METHODS

Between 2020 and 2022, 610,437 paired TFT results were collected from six university hospitals. The absolute DCL (absDCL) was determined using the 95th percentile for each clinical setting from a random 60 % of the total data. These absDCLs were then tested within and across different settings using the remaining 40 % of the data, alongside mix-up datasets for result and sample comparisons. The sensitivities of absDCL were calculated within and across groups in the mix-up datasets.

RESULTS

Health screening absDCLs were notably lower than in other settings (2.58 vs. 5.93-7.08 for thyroid-stimulating hormone; 4.12 vs. 8.24-10.04 for free thyroxine; 0.49 vs. 0.82-0.91 for total triiodothyronine). The proportion of results exceeding absDCL of health screening differed from those of other clinical settings. Furthermore, sensitivity between health screening and other clinical settings was significantly different in both the result mix-up and sample mix-up datasets.

CONCLUSIONS

This study determined practical DCLs for TFTs and highlighted differences in absDCLs between health screening and other settings. These findings emphasize the importance of tailored DCLs in improving the accurate reporting of TFTs.

Agreement between routinely used immunoassays for thyroid function testing in non-pregnant and pregnant adults

OBJECTIVE

Thyroid function tests are common biochemical analyses, and agreement between the routinely used immunoassays is important for diagnosis and monitoring of thyroid disease. Efforts are continuously made to align the biochemical assays, and we aimed to evaluate the agreement between immunoassays used in a clinical laboratory setting among non-pregnant and pregnant adults.

DESIGN

Cross-sectional study.

PARTICIPANTS

Serum samples were obtained from 192 blood donors (non-pregnant adults) and from 86 pregnant women in the North Denmark Region with no known thyroid disease.

MEASUREMENTS

Each sample was used for measurement of thyroid-stimulating hormone (TSH) with the routinely used automatic immunoassays in the regional Departments of Clinical Biochemistry (Alinity, Abbott Laboratories, Cobas, Roche Diagnostics, and Atellica, Siemens Healthineers) and reported as the median with 95% confidence interval (95% CI).

RESULTS

In nonpregnant adults, the level of TSH was higher with Cobas and Atellica than with Alinity as reflected by median (Alinity: 1.39 mIU/L (95% CI: 1.30-1.51 mIU/L); Cobas: 1.57 mIU/L (95% CI: 1.48-1.75 mIU/L); Atellica: 1.74 mIU/L (95% CI: 1.61-1.83 mIU/L)). Similarly, a trend was seen towards higher median TSH with Cobas than with Alinity among pregnant women (Alinity: 1.90 mIU/L (95% CI: 1.37-2.82 mIU/L); Cobas: 2.33 mIU/L (95% CI: 1.69-3.62 mIU/L)).

CONCLUSION

Results of thyroid function tests obtained with different immunoassays were not interchangeable when evaluated among pregnant and non-pregnant adults. The distinct differences are relevant for clinical decision making and emphasize the necessity of clinical laboratory information when different assays are used for diagnosis and monitoring of patients with thyroid disease.

Deciphering the roles of triiodothyronine (T3) and thyroid-stimulating hormone (TSH) on cardiac electrical remodeling in clinical and experimental hypothyroidism

Hypothyroidism is the most frequent endocrine pathology. Although clinical or overt hypothyroidism has been traditionally associated to low T3 / T4 and high thyrotropin (TSH) circulating levels, other forms exist such as subclinical hypothyroidism, characterized by normal blood T3 / T4 and high TSH. In its different forms is estimated to affect approximately 10% of the population, especially women, in a 5:1 ratio with respect to men. Among its consequences are alterations in cardiac electrical activity, especially in the repolarization phase, which is accompanied by an increased susceptibility to cardiac arrhythmias. Although these alterations have traditionally been attributed to thyroid hormone deficiency, recent studies, both clinical trials and experimental models, demonstrate a fundamental role of TSH in cardiac electrical remodeling. Thus, both metabolic thyroid hormones and TSH regulate cardiac ion channel expression in many and varied ways. This means that the different combinations of hormones that predominate in different types of hypothyroidism (overt, subclinic, primary, central) can generate different forms of cardiac electrical remodeling. These new findings are raising the relevant question of whether serum TSH reference ranges should be redefined.