Pitfalls in the measurement and interpretation of thyroid function tests

Increased Central and Peripheral Thyroid Resistance Indices During the First Half of Gestation Were Associated With Lowered Risk of Gestational Diabetes-Analyses Based on Huizhou Birth Cohort in South China

OBJECTIVES

The study aimed to explore the relationship of thyroid function and resistance indices with subsequent risk of gestational diabetes (GDM).

DESIGN

This was a longitudinal study embedded in the Huizhou Birth Cohort.

METHODS

A total of 2,927 women of singleton pregnancy were recruited from January to October of 2019. Thyroid central resistance indices were evaluated by Thyroid Feedback Quartile-Based index (TFQI), Thyrotrophy T4 Resistance Index (TT4RI), and TSH Index (TSHI) based on plasma-free thyroxine (FT4) and thyroid-stimulating hormone (TSH) levels during the first half of pregnancy. Thyroid peripheral sensitivity was assessed by free triiodothyronine (FT3) to FT4 ratio (FT3/FT4), a proxy of deiodinase activity. GDM was diagnosed between 24 and 28 weeks of gestation by a standardized 75 g oral glucose tolerance test. Multivariable linear and logistic regression was applied to examine the associations of thyroid markers with GDM risk.

RESULTS

FT3 and FT3/FT4 were positively associated with both fasting and post-load glucose levels, while TSH, TSHI, TT4RI, and TFQI were negatively associated with 1 and 2 h post-load glucose levels. Compared with the lowest quartile, GDM risk in the highest quartile increased by 44% [odds ratio (OR) = 1.44; 95%CI, 1.08-1.92; p_trend = 0.027] for FT3 and 81% (OR = 1.81; 95%CI, 1.33-2.46; p_trend < 0.001) for FT3/FT4, while it lowered by 37% (OR = 0.63; 95%CI, 0.47-0.86; p_trend = 0.002] for TSHI, 28% for TT4RI (OR = 0.72; 95%CI, 0.54-0.97; p_trend = 0.06), and 37% for TFQI (OR = 0.63; 95%CI, 0.46-0.85; p_trend < 0.001).

CONCLUSIONS

This longitudinal study indicated that higher FT3 and FT3/FT4 and lower central thyroid resistance indices were associated with increased risk of GDM.

Impaired sensitivity to thyroid hormones and carotid plaque in patients with coronary heart disease: A RCSCD-TCM study in China

CONTEXT

Previous studies on the association between thyroid function and carotid plaque have shown contradictory results, which may be attributable to the sensitivity to thyroid hormone indices. This study aimed to analyze the association between thyroid hormone sensitivity and risk of carotid plaque in patients with coronary heart disease (CHD) and further explore this association according to sex, age, smoking, and drinking status.

METHODS

This large-scale, multi-center, retrospective, cross-sectional study included 6679 patients with CHD (age 35-75). Central sensitivity to thyroid hormone was evaluated by the thyroid feedback quantile-based index (TFQI), parametric thyroid feedback quantile-based index (PTFQI), thyroid-stimulating hormone index (TSHI), and thyrotroph thyroxine resistance index (TT4RI). Peripheral sensitivity to thyroid hormone was assessed by free triiodothyronine/free thyroxine (FT3/FT4) ratio. Taking no carotid plaque as a reference, this study used logistic regression to analyze the association between central and peripheral thyroid hormone sensitivity and carotid plaque in patients with CHD.

RESULTS

Of the 6679 patients with CHD, 4843 (72.50%) had carotid plaque. In the multi-adjusted models, the TFQI (odds ratio [OR]: 1.50; 95% confidence interval [CI]: 1.26-1.78; P < 0.001), PTFQI (OR: 1.76; 95% CI: 1.46-2.12; P < 0.001), TSHI (OR: 1.21; 95% CI: 1.10-1.33; P < 0.001), and TT4RI (OR: 1.00; 95% CI: 1.00-1.01; P = 0.003) were positively associated with the risk of carotid plaque. Compared with that in females and people > 60 years, the OR value for carotid plaque was higher in males and people ≤ 60 years. Similarly, smokers and drinkers had higher OR values for carotid plaque than non-smokers and non-drinkers. Conversely, FT3/FT4 ratio (OR: 0.75; 95% CI: 0.70-0.81; P < 0.001) was negatively associated with carotid plaque, and the OR value for carotid plaque was lower in males, patients ≤ 60 years, smokers, and drinkers.

CONCLUSION

This study showed that thyroid hormone sensitivity is significantly associated with carotid plaque in patients with CHD. This association is more significant in males, patients ≤ 60 years, smokers, and drinkers.

Simultaneous Coexistence of Thyrotropin-Prolactin-Secreting Adenoma and Papillary Thyroid Carcinoma

Background

The thyrotropin-secreting adenomas are very rare and even more rare when they simultaneously coexist with thyroid carcinoma. So far, only sixteen cases have been reported in the literature. Here, we present a unique case of successful management of a concurrent case of thyrotropin-prolactinoma with papillary thyroid carcinoma. Case Presentation. A 50-year-old Moroccan woman underwent a total thyroidectomy and complementary totalization by iratherapy for papillary thyroid carcinoma, who presented persistence of an inappropriate secretion of the thyroid-stimulating hormone (TSH > 4 mUI/L) despite of levothyroxine suppressive therapy (300 μg/d). After eliminating noncompliance, interfering medicines, and thyroid malabsorption, a pituitary adenoma (12 mm) was documented at magnetic resonance imaging. The patient has had transsphenoidal pituitary adenomectomy with histology confirming a thyrotropin-prolactin-secreting adenoma. After surgery and lanreotide treatment failures, we noted a complete response (TSH < 0.5) with cabergoline treatment (3 mg/week).

Conclusion

The unusual association of thyroid adenocarcinoma and TSHoma enriches the hypothesis of a potential link between thyrotropic hypersecretion and thyroid carcinogenesis. Our case also illustrates the difficulty of monitoring thyroid carcinoma in nonremission of a TSHoma.

Free triiodothyronine (T3) is negatively associated with fasting ghrelin serum levels in a population sample of euthyroid subjects

PURPOSE

Ghrelin is an orexigenic peptide hormone secreted in times of stress and hunger. It is deeply involved in the regulation of metabolism and energy homeostasis, promoting energy intake and inhibiting energy expenditure on a metabolic level. In this regard, it has in many ways antagonistic effect on the thyroid hormones, which increase metabolism and thus energy expenditure. While there is reasonable evidence of a negative association between ghrelin and hormones of the hypothalamic-pituitary-thyroid (HPT-) axis from studies in patients with thyroid dysfunction and small intervention studies, large-scale studies in healthy subjects are lacking. Therefore, we studied the relationship between total ghrelin serum levels and serum levels of the thyroid hormones in a large sample of euthyroid subjects.

METHODS

Total ghrelin, thyroid-stimulating hormone (TSH), free thyroxine (fT4) and free triiodothyronine (fT3) were determined after an overnight fast in 1666 subjects participating in a population-based cross-sectional study ('LIFE') including 10,000 adults. 1012 subjects were included in this analysis. Multiple linear regression analyses were performed.

RESULTS

FT3 was negatively associated with serum ghrelin; total sample: β = - 0.0001, p < 0.001; men: β = - 0.0002, p = 0.013; women: β = - 0.0001, p = 0.010, adjusted for age, BMI, alcohol consumption, serum levels of TSH and fT4 and smoking status. No associations were found between ghrelin serum levels and serum levels of fT4 or TSH.

CONCLUSION

This is to date the largest study investigating the relationship between total serum ghrelin and thyroid hormones. The results point to a complex interaction and should initiate further research.

Clinical Consequences of Variable Results in the Measurement of Free Thyroid Hormones: Unusual Presentation of a Family with a Novel Variant in the THRB Gene Causing Resistance to Thyroid Hormone Syndrome

INTRODUCTION

Resistance to thyroid hormone β (RTHβ) is an inherited syndrome caused by dominant negative variants in the THRB gene (NM_000461.5). The clinical picture of RTHβ is variable, and patients harboring the same variant may display different degrees of disease severity.

CASE PRESENTATION

A 30-year-old man presented with thyrotoxicosis and central hyperthyroidism and was found to have a novel variant in the exon 10 of THRB gene (c.C1282G, p.L428V), located within the third hot spot region of the C-terminal of the receptor. Surprisingly, the same variant was found in two other relatives with an apparent normal thyroid function at initial screening. After exclusion of a TSH-secreting adenoma and serum interference in the proband, and the finding that exogenous levothyroxine failed to suppress the TSH in the brother affected by nodular goiter, relatives' thyroid function tests (TFTs) were reassessed with additional analytical method revealing biochemical features consistent with RTHβ in all carriers of the p.L428V variant. Functional studies showed a slightly impaired in vitro transcriptional activity of p.L428V. Interestingly' the expression of the human p.L428V thyroid hormone receptor beta in the zebrafish embryo background generated a phenotype consistent with RTHβ.

CONCLUSION

Variable results of TFTs on some immunoassays can be a cause of RTHβ diagnostic delay, but the genotype-phenotype correlation in this family and functional studies support p.L428V as a novel THRB variant expanding the spectrum of gene variants causing RTHβ. In vivo, rather than in vitro, functional assays may be required to demonstrate the dominant negative action of THRB variants.

Thyroid Disfunction in Critically Ill COVID-19 Patients. Relationship with In-Hospital Mortality

The incidence of thyroid disfunction has not been analyzed in critically ill COVID-19 patients. Our objective was to analyze the relationship of the thyroid profile and in-hospital mortality in critically ill COVID-19 patients. This was a prospective single-center study involving critically ill COVID-19 patients admitted to the ICU of a tertiary University Hospital. Thyroid hormones were measured through drawing blood samples from a central venous catheter at ICU admission and on the fifth day. A multiple logistic regression analysis was performed to analyze the variables associated with mortality. The ability of the different thyroid hormones to predict in-hospital mortality was evaluated by calculating the receiver operating characteristics (ROCs) and the area under the curve (AUC). A total of 78 patients were included in the study at ICU admission; 72 had their thyroid profile measured at day 5. In-hospital mortality reached 29.5%. Multiple logistic regression analysis showed that variables associated with mortality were age and prior beta-blocker therapy at ICU admission and age fT4 at day 5. The AUC for in-hospital mortality predictions of fT4 at day 5 was 0.69. Thyroid responses are commonly observed in critically ill COVID-19 patients. fT4 at day 5 after ICU admission was associated with mortality.

Rapid molecular diagnosis of ALB gene variants prevents unnecessary interventions in familial dysalbuminemic hyperthyroxinemia

OBJECTIVES

Familial dysalbuminemic hyperthyroxinemia (FDH) is an autosomal dominant condition caused by heterozygous gain-of-function mutations in the human ALB gene.

CASE PRESENTATION

We report, a three-year-old boy with FDH due to p.R242P (or p.R218P without signal peptide) mutation in the ALB gene with a phenotype characterized by extremely high serum total and free thyroxine concentrations. His parents had normal thyroid function tests (TFT), so the mutation detected in this patient is assumed "de novo". Although the most frequent variant was p.R242H in Caucasians and p.R242P in Japanese, our patient had p.R242P variant.

CONCLUSIONS

Early identification of FDH is fundamental to prevent unnecessary repeats of TFT with different methods. We encourage the ALB gene hot spot sequencing initially and indicate that this molecular diagnosis is a rapid and simple method to diagnose FDH in individuals with euthyroid hyperthyroxinemia.

Thyroid and COVID-19: a review on pathophysiological, clinical and organizational aspects

BACKGROUND

Thyroid dysfunction has been observed in patients with COVID-19, and endocrinologists are requested to understand this clinical issue. Pandemic-related restrictions and reorganization of healthcare services may affect thyroid disease management.

OBJECTIVE AND METHODS

To analyze and discuss the relationship between COVID-19 and thyroid diseases from several perspectives. PubMed/MEDLINE, Google Scholar, Scopus, ClinicalTrial.gov were searched for this purpose by using free text words and medical subject headings as follows: "sars cov 2", "covid 19", "subacute thyroiditis", "atypical thyroiditis", "chronic thyroiditis", "hashimoto's thyroiditis", "graves' disease", "thyroid nodule", "differentiated thyroid cancer", "medullary thyroid cancer", "methimazole", "levothyroxine", "multikinase inhibitor", "remdesivir", "tocilizumab". Data were collected, analyzed, and discussed to answer the following clinical questions: "What evidence suggests that COVID-19 may induce detrimental consequences on thyroid function?"; "Could previous or concomitant thyroid diseases deteriorate the prognosis of COVID-19 once the infection has occurred?"; "Could medical management of thyroid diseases influence the clinical course of COVID-19?"; "Does medical management of COVID-19 interfere with thyroid function?"; "Are there defined strategies to better manage endocrine diseases despite restrictive measures and in-hospital and ambulatory activities reorganizations?".

RESULTS

SARS-CoV-2 may induce thyroid dysfunction that is usually reversible, including subclinical and atypical thyroiditis. Patients with baseline thyroid diseases are not at higher risk of contracting or transmitting SARS-CoV-2, and baseline thyroid dysfunction does not foster a worse progression of COVID-19. However, it is unclear whether low levels of free triiodothyronine, observed in seriously ill patients with COVID-19, may worsen the disease's clinical progression and, consequently, if triiodothyronine supplementation could be a tool for reducing this burden. Glucocorticoids and heparin may affect thyroid hormone secretion and measurement, respectively, leading to possible misdiagnosis of thyroid dysfunction in severe cases of COVID-19. High-risk thyroid nodules require a fine-needle aspiration without relevant delay, whereas other non-urgent diagnostic procedures and therapeutic interventions should be postponed.

DISCUSSION

Currently, we know that SARS-CoV-2 could lead to short-term and reversible thyroid dysfunction, but thyroid diseases seem not to affect the progression of COVID-19. Adequate management of patients with thyroid diseases remains essential during the pandemic, but it could be compromised because of healthcare service restrictions. Endocrine care centers should continuously recognize and classify priority cases for in-person visits and therapeutic procedures. Telemedicine may be a useful tool for managing patients not requiring in-person visits.

A Clinical Debate: Subclinical Hypothyroidism

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Reference Intervals of Thyroid Function Tests Assessed by Immunoassay and Mass Spectrometry in Healthy Pregnant Women Living in Catalonia

BACKGROUND

Recent guidelines recommend establishing a local reference interval (RI) for thyroid function. We aimed to establish trimester-specific RIs for thyrotropin (TSH) and free thyroxine (FT4) in a cohort of healthy pregnant women in Catalonia (Spain).

METHODS

A prospective observational study was conducted with 332 healthy pregnant women, from the first trimester (1T) to delivery. TSH was measured using an Architect^® immunoassay (Abbott) and FT4 by two immunoassays, Architect^® (Abbott) and Cobas^® (Roche), in the three trimesters. FT4 was also measured by liquid chromatography mass spectrometry (LC/MS/MS) in the 1T.

RESULTS

TSH (µUI/mL) increased throughout pregnancy (1T: 0.03-3.78; 2T: 0.51-3.53; 3T: 0.50-4.32; p < 0.0001) and FT4 (pmol/L) progressively decreased (Architect^® 1T: 10.42-15.96; 2T: 8.37-12.74; 3T: 8.24-12.49; p < 0.0001; and Cobas^®: 1T: 11.46-19.05; 2T: 9.65-14.67; 3T: 8.88-14.54; p < 0.0067). The FT4 RI during 1T determined LC/MS/MS was 8.75-18.27. Despite the 1T FT4 results measured by LC/MS/MS and with the two immunoassays being significantly correlated, the results obtained by the three methods were found to be non-interchangeable.

CONCLUSIONS

We established trimester-specific RIs for TSH and for FT4 with immunoassays in our population. We also validated the 1T FT4 using LC/MS/MS to confirm the results of FT4 lower than the 2.5th percentile or higher than the 97.5th percentile.

The Health Impacts of Hazardous Chemical Exposures among Child Labourers in Low- and Middle-Income Countries

Of 218 million working children worldwide, many are suspected to be exposed to hazardous chemicals. This review aims to synthesize reported evidence over the last two decades on chemical exposure and adverse health consequences in children labourers in low- and middle-income Countries (LMIC). Included studies investigated health outcomes related to chemical exposures among child labourers aged 5-18 in LMIC. Twenty-three papers were selected for review, focusing on pesticides (n = 5), solvents (n = 3), metals (n = 13) and persistent organic pollutants (POPs) (n = 2). Adverse health effects identified among child labourers included abnormal biomarkers, for example elevated blood and urine chemical concentrations, neurobehavioural deficits and neurological symptoms, mental health issues, oxidative stress and DNA damage, poor growth, asthma, and hypothyroidism. Workplace exposure to chemicals has pernicious health effects on child labourers. Large research gaps exist, in particular for long-term health impacts through chronic conditions and diseases with long latencies. A sizeable disease burden in later life is likely to be directly attributable to chemicals exposures. We urge national and international agencies concerned with child labour and occupational health, to prioritize research and interventions aiming to reduce noxious chemical exposures in workplaces where children are likely to be present.

Pediatric reference intervals for endocrine markers and fertility hormones in healthy children and adolescents on the Siemens Healthineers Atellica immunoassay system

OBJECTIVES

Rapid development in childhood and adolescence combined with lack of immunoassay standardization necessitates the establishment of age-, sex-, and assay-specific reference intervals for immunochemical markers. This study established reference intervals for 11 immunoassays on the new Siemens Healthineers Atellica® IM Analyzer in the healthy CALIPER cohort.

METHODS

A total of 600 healthy participants (birth to 18 years) were recruited from the community, and serum samples were collected with informed consent. After sample analysis, age- and sex-specific differences were assessed, and outliers were removed. Reference intervals were established using the robust method (40-<120 participants) or nonparametric method (≥120 participants).

RESULTS

Of the 11 immunoassays studied, nine required age partitioning (i.e., dehydroepiandrosterone-sulfate, estradiol, ferritin, folate, follicle-stimulating hormone, luteinizing hormone, progesterone, testosterone, vitamin B12), and seven required sex partitioning. Free thyroxine and thyroid-stimulating hormone demonstrated no significant age- and/or sex-specific differences.

CONCLUSIONS

Overall, the age- and sex-specific trends observed closely mirrored those previously reported by CALIPER on other platforms as well as other internationally recognized studies. However, established lower and upper limits demonstrated some discrepancies between published values from healthy cohorts on alternate analytical systems, highlighting differences between manufacturers and the need for platform-specific reference intervals for informed pediatric clinical decision-making.

Variation in Normal Range Thyroid Function Affects Serum Cholesterol Levels, Blood Pressure, and Type 2 Diabetes Risk: A Mendelian Randomization Study

Background: Observational studies have demonstrated that variation in normal range thyroid function is associated with major cardiovascular risk factors, including dyslipidemia, hypertension, type 2 diabetes (T2D), and obesity. As observational studies are prone to residual confounding, reverse causality, and selection bias, we used a Mendelian randomization (MR) approach to investigate whether these associations are causal or not. Methods: Two-sample MR analysis using data from the largest available genome-wide association studies on normal range thyrotropin (TSH) and free thyroxine (fT4) levels, serum lipid levels, blood pressure measurements, T2D, and obesity traits (body mass index [BMI] and waist/hip ratio). Results: A one standard deviation (SD) increase in genetically predicted TSH levels was associated with a 0.037 SD increase in total cholesterol levels (p = 3.0 × 10-4). After excluding pleiotropic instruments, we also observed significant associations between TSH levels and low-density lipoprotein levels (β = 0.026 SD, p = 1.9 × 10-3), pulse pressure (β = -0.477 mmHg, p = 7.5 × 10-10), and T2D risk (odds ratio = 0.95, p = 2.5 × 10-3). While we found no evidence of causal associations between TSH or fT4 levels and obesity traits, we found that a one SD increase in genetically predicted BMI was associated with a 0.075 SD decrease in fT4 levels (p = 3.6 × 10-4). Conclusions: Variation in normal range thyroid function affects serum cholesterol levels, blood pressure, and T2D risk.

Profiling retrospective thyroid function data in complete thyroidectomy patients to investigate the HPT axis set point (PREDICT-IT)

BACKGROUND

The homeostatic euthyroid set point of the hypothalamus-pituitary-thyroid axis of any given individual is unique and oscillates narrowly within substantially broader normal population ranges of circulating free thyroxine (FT4) and thyroid-stimulating hormone (TSH), otherwise termed 'thyroid function test (TFT)'. We developed a mathematical algorithm codenamed Thyroid-SPOT that effectively reconstructs the personalized set point in open-loop situations and evaluated its performance in a retrospective patient sample.

METHODS

We computed the set points of 101 patients who underwent total thyroidectomy for non-functioning thyroid disease using Thyroid-SPOT on each patient's own serial post-thyroidectomy TFT. Every predicted set point was compared against its respective healthy pre-operative euthyroid TFT per individual and their separation (i.e. predicted-observed TFT) quantified.

RESULTS

Bland-Altman analysis to measure the agreement between each pair of an individual's predicted and actual set points revealed a mean difference in FT4 and TSH of + 3.03 pmol/L (95% CI 2.64, 3.43) and - 0.03 mIU/L (95% CI - 0.25, 0.19), respectively. These differences are small compared to the width of the reference intervals. Thyroid-SPOT can predict the euthyroid set point remarkably well, especially for TSH with a 10-16-fold spread in magnitude between population normal limits.

CONCLUSION

Every individual's equilibrium euthyroid set point is unique. Thyroid-SPOT serves as an accurate, precise and reliable targeting system for optimal personalized restoration of euthyroidism. This algorithm can guide clinicians in L-thyroxine dose titrations to resolve persistent dysthyroid symptoms among challenging cases harbouring "normal TFT" within the laboratory ranges but differing significantly from their actual euthyroid set points.

Suppression of thyrotropin secretion during roxadustat treatment for renal anemia in a patient undergoing hemodialysis

Background

Inhibition of hypoxia-inducible factor prolyl hydroxylase (HIF-PH) is a novel choice for the treatment of renal anemia, and an oral HIF-PH inhibitor roxadustat was approved for renal anemia. Roxadustat has high affinity to thyroid hormone receptor beta, which may affect thyroid hormone homeostasis.

Case presentation

We present here a patient undergoing hemodialysis with primary hypothyroidism receiving levothyroxine replacement, who showed decreased free thyroxine (FT4) and thyroid stimulating hormone (TSH) after starting roxadustat. Pituitary stimulation test revealed selective suppression of TSH secretion. Recovery of TSH and FT4 levels after stopping roxadustat suggested the suppression of TSH was reversible.

Conclusions

Physicians should pay special attention to thyroid hormone abnormalities in treatment with roxadustat.

Inflammation-Related Markers and Thyroid Function Measures in Pediatric Patients: Is the Grade of Obesity Relevant?

We aimed to investigate the effect of weight status on inflammation-related markers and thyroid function tests in overweight and obese pediatric patients. Children and adolescents diagnosed between January 2017 and January 2019 with overweight or obesity were included in the study. Neutrophil-to-lymphocyte ratio (NLR), platelet-to lymphocyte ratio (PLR) and systemic immune-inflammation index (SII) were calculated for the groups defined according to Body Mass Index (BMI)-for-age z-score: overweight (≥1 BMI-for-age z-score), obese (≥2 BMI-for-age z-score) and severely obese (≥3 BMI-for-age z-score). Severely obese patients had significantly higher value of white blood cells (WBC) counts (median = 7.92) compared with overweight patients (7.37, p = 0.014). Absolute lymphocyte count was significantly associated with obesity degree in children (Spearman’s Rho coefficient ρ = 0.228. p = 0.035), whereas absolute polymorphonuclear neutrophils (PMNCs) count was significantly higher in severely obese adolescents than overweight adolescents (overweight: 4.04 vs. severely obese: 5.3 (p = 0.029)). In 8.19% of patients an elevated thyroid-stimulating hormone (TSH) level was found, and 3.36% of patients had a low level of free thyroxine with an elevated level of TSH. Total absolute WBC count may be a reliable inflammation-related marker in obese pediatric patients without metabolic syndrome, but needs to be validated in the context of all possible covariates. Subclinical and overt hypothyroidism may develop from an early age in overweight or obese patients.

Determination of 3-iodothyronamine (3-T1AM) in mouse liver using liquid chromatography-tandem mass spectrometry

3-iodothyronamine (3-T₁AM) has been suggested as a novel chemical messenger and potent trace amine-associated receptor 1 ligand in the CNS that occurs naturally as endogenous metabolite of the thyroid hormones. Discrepancies and variations in 3-T₁AM plasma and tissue concentrations have nonetheless caused controversy regarding the existence and biological role of 3-T₁AM. These discussions are at least partially based on potential analytical artefacts caused by differential decay kinetics of 3-T₁AM and the widely used deuterated quantification standard D₄-T₁AM. Here, we report a novel LC-MS/MS method for the quantification of 3-T₁AM in biological specimens using stable isotope dilution with ¹³C₆-T₁AM, a new internal standard that showed pharmacodynamic properties comparable to endogenous 3-T₁AM. The method detection limit (MDL) and method quantification limit (MQL) of 3-T₁AM were 0.04 and 0.09 ng/g, respectively. The spike-recoveries of 3-T₁AM were between 85.4% and 94.3%, with a coefficient of variation of 3.7-5.8%. The intra-day and inter-day variations of 3-T₁AM were 8.45-11.2% and 3.58-5.73%, respectively. Endogenous 3-T₁AM liver values in C57BL/6J mice were 2.20 ± 0.49 pmol/g with a detection frequency of 50%. Higher liver 3-T₁AM values were found when C57BL/6J mice were treated with N-acetyl-3-iodothyronamine or O-acetyl-3-iodothyronamine. Overall, our new stable isotope dilution LC-MS/MS method improves both the sensitivity and selectivity compared with existing methods. The concomitant possibility to quantify additional thyroid hormones such as thyroxine, 3,5,3'-triiodo-_L-thyronine, 3,3',5'-triiodo-_L-thyronine, 3,3'-diiodo-_L-thyronine, and 3,5-diiodo-_L-thyronine further adds to the value of our novel method in exploring the natural occurrence and fate of 3-T₁AM in biological tissues and fluids.

The role of laboratory medicine in the diagnosis of the hyperthyroidism

Hyperthyroidism is a clinical condition characterized by inappropriately high synthesis and secretion of thyroid hormones by the thyroid gland. It has multiple aetiologies, manifestations and potential therapies. Graves' disease is the most common form of hyperthyroidism, due to the production of autoantibodies against thyrotropin receptor, capable of over-stimulating thyroid function. A reliable diagnosis of hyperthyroidism can be established on clinical grounds, followed by the evaluation of serum thyroid function tests (thyrotropin first and then free thyroxine, adding the measurement of free triiodothyronine in selected specific situations). The recent guidelines of both the American and European Thyroid Associations have strongly recommended the measurement of thyrotropin receptor autoantibodies for the accurate diagnosis and management of Graves' disease. If autoantibody test is negative, a radioiodine uptake should be performed. Considering the most recent laboratory improvements, binding assays can be considered the best first solution for the measurement of thyrotropin receptor autoantibodies in diagnosis and management of overt cases of Graves' disease. In fact, they have a satisfactory clinical sensitivity and specificity (97.4% and 99.2%, respectively) being performed in clinical laboratories on automated platforms together with the other thyroid function tests. In this setting, the bioassays should be reserved for fine and complex diagnoses and for particular clinical conditions where it is essential to document the transition from stimulating to blocking activity or vice versa (e.g. pregnancy and post-partum, related thyroid eye disease, Hashimoto's thyroiditis with extrathyroidal manifestations, unusual cases after LT4 therapy for hypothyroidism or after antithyroid drug treatment for Graves' disease). Undoubtedly, technological advances will help improve laboratory diagnostics of hyperthyroidism. Nevertheless, despite future progress, the dialogue between clinicians and laboratory will continue to be crucial for an adequate knowledge and interpretation of the laboratory tests and, therefore, for an accurate diagnosis and correct management of the patient.

Rapid determination of thyroid hormones in blood plasma from Glaucous gulls and Baikal seals by HybridSPE®-LC-MS/MS

A rapid hybrid solid phase extraction (HybridSPE®) protocol tailored to liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) analysis, was developed for the determination of four thyroid hormones, L-Thyroxine (T₄), 3,3',5-triiodo-L-thyronine (T₃), 3,3',5'-triiodo-L-thyronine (rT₃) and 3,3'-diiodo-L-thyronine (T₂) in blood plasma from Glaucous gulls (Larus hyperboreus) and Baikal seals (Phoca sibirica). The use of target analyte specific ¹³C internal standards allowed quantification to be performed through the standard solvent calibration curves and alleviated the need to perform quantification with matrix match curves. The relative recoveries were 100.0-110.1 % for T₄, 99.1-102.2 % for T₃, 100.5-108.0 % for rT₃, and 100.5-104.6 % for T₂. The matrix effects ranged from -1.52 to -6.10 %, demonstrating minor signal suppression during analysis. The method intra-day precision (method repeatability, RSD %, N = 5, k = 1 day) and inter-day precision (method reproducibility, RSD %, N = 10, k = 2 days) at the 1 ng/mL concentration of fortification were 8.54-15.4 % and 15.4-24.8 %, respectively, indicating acceptable chromatographic peak stabilities for all target THs even at trace level concentrations. The method limit of detection (LOD) for T₄, T₃, rT₃ and T₂ was 0.17, 0.16, 0.30 and 0.17 ng/mL, respectively. The HybridSPE® protocol was simple and rapid (<1 min) upon application, while the HybridSPE® cartridge did not require (as in classical SPE cartridges) any additional equilibration nor conditioning step prior sample loading. A total of 46 blood plasma samples, 30 samples collected from Glaucous gulls and 16 samples collected from Baikal seals, were analyzed for thyroid hormones to demonstrate the applicability of the developed method in these wildlife species. The concentrations of T₄ and T₃ in blood plasma from the Glaucous gulls were 5.95-44.2 and 0.37-5.61 ng/mL, respectively, whereas those from Baikal seals were 3.57-46.5 and 0.45-2.07 ng/mL, respectively. In both species, rT₃ demonstrated low detection rate, while T₂ was not detected. Furthermore, cross-array comparison between the HybridSPE®-LC-MS/MS protocol and an established routine radioimmunoassay (RIA) kit-based method was performed for T₄ and T₃ concentrations from selected Baikal seal plasma samples.

Les médicaments qui interfèrent avec les bilans biologiques : revue de la littérature

BACKGROUND

Biological assessment is an integral part of the diagnostic process that guides therapeutic management decisions. However, these analyses remain subject to interference from endogenous or exogenous factors, which may alter the results.

OBJECTIVE

To provide an up-to-date and comprehensive overview of the most commonly documented types of interference attributable to medications, to ensure reliable interpretation of test results and better management of patients.

DATA SOURCES

This comprehensive systematic review of the literature was carried out in 2018. The bibliographic search was carried out in various online databases, specifically PubMed, ScienceDirect and Google Scholar.

STUDY SELECTION

Only publications in French or English concerning medicinal products for human use were retained. The investigators' examination of drug-related interference with laboratory tests was limited to blood assays (serum or plasma).

DATA EXTRACTION

An Excel spreadsheet was used to analyze the results. A total of 82 articles were selected. The interferences studied affected 47 biological parameters corresponding to various types of assessment: hormonal, hepatic, and renal.

DATA SYNTHESIS

The mechanisms reported in the literature identified were analytical (56.9%), physiological (17.82%), and pharmacological (20.11%). The remainder of the mechanisms (5.17%) were not defined.

CONCLUSIONS

Clinicians should be vigilant in validating and interpreting laboratory test results for patients receiving these types of drugs. Dialogue between clinicians and biological scientists is the best way to avoid unnecessary additional testing, which is often cumbersome and costly.

Increased Thyroid-Hormone Requirements Consistent With Type 3 Deiodinase Induction Related to Ibrutinib in a Thyroidectomized Woman

Objective

Tyrosine-kinase inhibitors (TKIs) are chemotherapeutic agents associated with increased thyroid-hormone requirements and altered deiodinase activity. We present the first case to link these findings to the TKI ibrutinib.

Methods

Serial thyroid-stimulating hormone (TSH), free-thyroxine (FT4), free-triiodothyronine (FT3), and reverse-triiodothyronine (rT3) levels were assessed.

Results

An 80-year-old, 62-kg woman with hypothyroidism secondary to total thyroidectomy for stage I papillary thyroid cancer, on maintenance levothyroxine (LT4) 137 μg daily, presented for follow-up. Compared to one year prior, the patient’s weight had increased by 2 kg and TSH from 2.58 to 27.60 μIU/mL (normal: 0.45-4.50 μIU/mL) while on pantoprazole. Ibrutinib, her other medication, had been started seven months prior for chronic lymphocytic leukemia. Despite sequential confirmation of proper LT4 adherence and self-administration, adjustment of LT4 to 150 μg, and discontinuation of pantoprazole, the patient’s hypothyroid symptoms worsened, and the TSH was 73.90 μIU/mL six months later. LT4 was increased to 175 μg six days a week and 262.5 μg once weekly. Two months later, the TSH was 3.92 μIU/mL (steady-state condition), FT4 2.32 ng/dL (normal: 0.82-1.77 ng/dL), FT3 1.6 pg/mL (normal: 2.0-4.4 pg/mL), and rT3 69.6 ng/dL (normal: 9.2-24.1 ng/dL). Ibrutinib was discontinued the next month due to gastrointestinal side effects and elevated blood pressure. Four months later, LT4 had been reduced to 150 μg, and the FT4 reached 1.92 ng/dL, FT3 2.0 pg/mL, and rT3 26.6 ng/dL.

Conclusion

This report links ibrutinib to increased thyroid-hormone requirements in a thyroidectomized woman whose decreased T3:T4, T3:rT3, and T4:rT3 ratios suggested type 3 deiodinase induction and type 2 deiodinase inhibition.

Managing symptoms in hypothyroid patients on adequate levothyroxine: a narrative review

The current standard of care for hypothyroidism is levothyroxine (LT4) monotherapy to reduce levels of thyrotropin (thyroid-stimulating hormone, TSH) within its reference range and amelioration of any symptoms. A substantial minority continues to report hypothyroid-like symptoms despite optimized TSH, however. These symptoms are not specific to thyroid dysfunction and are frequent among the euthyroid population, creating a therapeutic dilemma for the treating clinician as well as the patient. We present a concise, narrative review of the clinical research and evidence-based guidance on the management of this challenging population. The clinician may endeavor to ensure that the serum TSH is within the target range. However, the symptomatic patient may turn to alternative non-evidence-based therapies in the hope of obtaining relief. Accordingly, it is important for the clinician to check for conditions unrelated to the thyroid that could account for the ongoing symptoms such as other autoimmune conditions, anemia or mental health disorders. Systematic and thorough investigation of the potential causes of persistent symptoms while receiving LT4 therapy will resolve the problem for most patients. There may be some patients that may benefit from additional treatment with liothyronine (LT3), although it is unclear as yet as to which patient group may benefit the most from combined LT4 + LT3 therapy. In the future, personalized treatment with LT4 + LT3 may be of benefit for some patients with persistent symptoms of hypothyroidism such as those with polymorphisms in the deiodinase enzyme 2 (DIO2). For now, this remains a subject for research.

Thyrotoxicosis in patients with COVID-19: the THYRCOV study

OBJECTIVE

This study assessed thyroid function in patients affected by the coronavirus disease-19 (COVID-19), based on the hypothesis that the cytokine storm associated with COVID-19 may influence thyroid function and/or the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may directly act on thyroid cells, such as previously demonstrated for SARS-CoV-1 infection.

DESIGN AND METHODS

This single-center study was retrospective and consisted in evaluating thyroid function tests and serum interleukin-6 (IL-6) values in 287 consecutive patients (193 males, median age: 66 years, range: 27-92) hospitalized for COVID-19 in non-intensive care units.

RESULTS

Fifty-eight patients (20.2%) were found with thyrotoxicosis (overt in 31 cases), 15 (5.2%) with hypothyroidism (overt in only 2 cases), and 214 (74.6%) with normal thyroid function. Serum thyrotropin (TSH) values were inversely correlated with age of patients (rho -0.27; P < 0.001) and IL-6 (rho -0.41; P < 0.001). In the multivariate analysis, thyrotoxicosis resulted to be significantly associated with higher IL-6 (odds ratio: 3.25, 95% confidence interval: 1.97-5.36; P < 0.001), whereas the association with age of patients was lost (P = 0.09).

CONCLUSIONS

This study provides first evidence that COVID-19 may be associated with high risk of thyrotoxicosis in relationship with systemic immune activation induced by the SARS-CoV-2 infection.

Hyperthyroxinemia with a non-suppressed TSH: how to confidently reach a diagnosis in this clinical conundrum

Disorders of thyroid function are among the commonest referrals to endocrinology. While interpretation of thyroid function testing is usually straightforward, accurate interpretation becomes significantly more challenging when the parameters do not behave as would be expected in normal negative feedback. In such cases, uncertainty regarding further investigation and management arises. An important abnormal pattern encountered in clinical practice is that of high normal or raised free thyroxine (fT4) with inappropriately non-suppressed or elevated thyroid-stimulating hormone (TSH). In this short review using two clinical vignettes, we examine the diagnostic approach in such cases. A diagnostic algorithm is proposed to ensure that a definitive diagnosis is reached in these challenging cases.

Pituitary society guidance: pituitary disease management and patient care recommendations during the COVID-19 pandemic-an international perspective

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the viral strain that has caused the coronavirus disease 2019 (COVID-19) pandemic, has presented healthcare systems around the world with an unprecedented challenge. In locations with significant rates of viral transmission, social distancing measures and enforced 'lockdowns' are the new 'norm' as governments try to prevent healthcare services from being overwhelmed. However, with these measures have come important challenges for the delivery of existing services for other diseases and conditions. The clinical care of patients with pituitary disorders typically involves a multidisciplinary team, working in concert to deliver timely, often complex, disease investigation and management, including pituitary surgery. COVID-19 has brought about major disruption to such services, limiting access to care and opportunities for testing (both laboratory and radiological), and dramatically reducing the ability to safely undertake transsphenoidal surgery. In the absence of clinical trials to guide management of patients with pituitary disease during the COVID-19 pandemic, herein the Professional Education Committee of the Pituitary Society proposes guidance for continued safe management and care of this population.

Low Yield of Thyroid-Function Tests in Adult Hospitalized Patients - A Retrospective Analysis

BACKGROUND

In the US, serum thyroid-stimulating hormone (TSH) and thyroxine measurements are the fourth- and tenth-commonest laboratory tests ordered, respectively. Diagnosis of thyroid disorder requires clinical suspicion supported by laboratory values. However, in the setting of acute illness, both the clinical and laboratory pictures can be confounded.

OBJECTIVE

To study clinical outcomes and derangement patterns of inpatient thyroid-function tests.

DESIGN

This retrospective study was conducted at an academic center on admissions aged ≥18 years and TSH tests performed over a 1-year period. Admissions with active pregnancy and/or prior thyroid-related diagnosis were excluded.

MAIN OUTCOMES

Clinical outcomes were divided based on new diagnosis of thyroid-related disorder, newly prescribed thyroxine replacement, or antithyroid drugs/ endocrinology referrals, or both. In order to analyze the derangement patterns of abnormal TSH, only the results of the first test ordered were considered (as some admissions had multiple TSH tests ordered).

RESULTS

A total of 7,204 admissions aged ≥18 years had TSH tests done. Of these, 1,912 were excluded. Of the 5,292 admissions with no prior thyroid disorder or active pregnancy, 183 (3.46%) were assigned a new diagnosis of thyroid-related disorder, 54 (1.02%) received treatment/referral, and 46 (0.87%) received both a new diagnosis and treatment/referral. Based on the TSH results (reference range 0.42-4.0 mIU/L) of the 5,292 admissions, 4,312 (81.5%) and 980 (18.5%) admissions were flagged normal and abnormal, respectively. Of the 980 admissions with one or more abnormal TSH results, 21 (2.14%) had first ordered TSH <0.05 mIU/L, 855 (87.25%) admissions had first TSH result between 0.05-10 mIU/L, and lastly 104 (10.61%) were >10 mIU/L.

CONCLUSION

There is low value in testing inpatients for thyroid disorders, and testing comes at significant expense to the health-care system.

Familial Dysalbuminemic Hyperthyroxinemia: An Underdiagnosed Entity

Resistance to thyroid hormone (RTH) is a syndrome characterized by impaired sensitivity of tissues to thyroid hormone (TH). The alteration of TH-binding proteins, such as in Familial Dysalbuminemic Hyperthyroxinemia (FDH), can mimic the abnormal serum thyroid tests typical of RTH. We aimed to characterize a population referred to our center with suspected RTH and estimate the proportion of patients with FDH. For 303 different families, we collected clinical and hormonal data and sequenced the thyroid hormone receptor β gene (THRB) and exon 7 of the albumin gene (ALB). We found 56 THRB variants (i.e., 38% of the 303 index cases, called RTHβ group). Among the samples screened for FDH variants, 18% had the variant R218H in ALB (FDH group); in addition, 71% of the cases had neither variant (non-FDH/RTHβ group). Patients with FDH had significantly lower free T3 (fT3) and free T4 (fT4) levels and more often an isolated elevation of fT4 than RTHβ patients. Clinically, patients with FDH had fewer symptoms than patients with RTHβ. Our study suggests that FDH should be systematically considered when examining patients suspected of having RTH. In most cases, they present no clinical symptoms, and their biochemical alterations show an elevation of fT4 levels, while fT3 levels are 1.11 times below the upper limit of the assay.

Management of thyrotoxicosis during pregnancy

Thyrotoxicosis during pregnancy should be adequately managed and controlled to prevent maternal and fetal complications. The evaluation of thyroid function in pregnant women is challenged by the physiological adaptations associated with pregnancy, and the treatment with antithyroid drugs (ATD) raises concerns for the pregnant woman and the fetus. Thyrotoxicosis in pregnant women is mainly of autoimmune origin, and the measurement of thyroid stimulating hormone-receptor antibodies (TRAb) plays a key role. TRAb helps to distinguish the hyperthyroidism of Graves' disease from gestational hyperthyroidism in early pregnancy, and to evaluate the risk of fetal and neonatal hyperthyroidism in late pregnancy. Furthermore, the measurement of TRAb in early pregnancy is recommended to evaluate the need for ATD during the teratogenic period of pregnancy. Observational studies have raised concern about the risk of birth defects associated with the use of ATD in early pregnancy and challenged the clinical management and choice of treatment.

Importance of Thyroid Hormone level and Genetic Variations in Deiodinases for Patients after Acute Myocardial Infarction: A Longitudinal Observational Study

This study aimed to examine the influence of thyroid hormone (TH) levels and genetic polymorphisms of deiodinases on long-term outcomes after acute myocardial infarction (AMI). In total, 290 patients who have experienced AMI were evaluated for demographic, clinical characteristics, risk factors, TH and NT-pro-BNP. Polymorphisms of TH related genes were included deiodinase 1 (DIO1) (rs11206244-C/T, rs12095080-A/G, rs2235544-A/C), deiodinase 2 (DIO2) (rs225015-G/A, rs225014-T/C) and deiodinase 3 (DIO3) (rs945006-T/G). Both all-cause and cardiac mortality was considered key outcomes. Cox regression model showed that NT-pro-BNP (HR = 2.11; 95% CI = 1.18– 3.78; p = 0.012), the first quartile of fT3, and DIO1 gene rs12095080 were independent predictors of cardiac-related mortality (HR = 1.74; 95% CI = 1.04–2.91; p = 0.034). The DIO1 gene rs12095080 AG genotype (OR = 3.97; 95% CI = 1.45–10.89; p = 0.005) increased the risk for cardiac mortality. Lower fT3 levels and the DIO1 gene rs12095080 are both associated with cardiac-related mortality after AMI.

CD5L Constitutes a Novel Biomarker for Integrated Hepatic Thyroid Hormone Action

Background: Pathological conditions of the thyroid hormone (TH) system are routinely diagnosed by using serum concentrations of thyrotropin (TSH), which is sufficient in most cases. However, in certain conditions, such as resistance to TH due to mutations in THRB (RTHb) or TSH-releasing pituitary adenoma (TSHoma), TSH may be insufficient for a correct diagnosis, even in combination with serum TH concentrations. Likewise, under TH replacement therapy, these parameters can be misleading and do not always allow optimal treatment. Hence, additional biomarkers to assess challenging clinical conditions would be highly beneficial. Methods: Data from untargeted multi-omics analyses of plasma samples from experimental thyrotoxicosis in human and mouse were exploited to identify proteins that might represent possible biomarkers of TH function. Subsequent mouse studies were used to identify the tissue of origin and the involvement of the two different TH receptors (TR). For in-depth characterization of the underlying cellular mechanisms, primary mouse cells were used. Results: The analysis of the plasma proteome data sets revealed 16 plasma proteins that were concordantly differentially abundant under thyroxine treatment compared with euthyroid controls across the two species. These originated predominantly from liver, spleen, and bone. Independent studies in a clinical cohort and different mouse models identified CD5L as the most robust putative biomarker under different serum TH states and treatment periods. In vitro studies revealed that CD5L originates from proinflammatory M1 macrophages, which are similar to liver-residing Kupffer cells, and is regulated by an indirect mechanism requiring the secretion of a yet unknown factor from hepatocytes. In agreement with the role of TRα1 in immune cells and the TRβ-dependent hepatocyte-derived signaling, the in vivo regulation of Cd5l expression depended on both TR isoforms. Conclusion: Our results identify several novel targets of TH action in serum, with CD5L as the most robust marker. Although further studies will be needed to validate the specificity of these targets, CD5L seems to be a promising candidate to assess TH action in hepatocyte-macrophage crosstalk.

Testing for thyroid hormone disruptors, a review of non-mammalian in vivo models

Thyroid hormones (THs) play critical roles in profound changes in many vertebrates, notably in mammalian neurodevelopment, although the precise molecular mechanisms of these fundamental biological processes are still being unravelled. Environmental and health concerns prompted the development of chemical safety testing and, in the context of endocrine disruption, identification of thyroid hormone axis disrupting chemicals (THADCs) remains particularly challenging. As various molecules are known to interfere with different levels of TH signalling, screening tests for THADCs may not rely solely on in vitro ligand/receptor binding to TH receptors. Therefore, alternatives to mammalian in vivo assays featuring TH-related endpoints that are more sensitive than circulatory THs and more rapid than thyroid histopathology are needed to fulfil the ambition of higher throughput screening of the myriad of environmental chemicals. After a detailed introduction of the context, we have listed current assays and parameters to assess thyroid disruption following a literature search of recent publications referring to non-mammalian models. Potential THADCs were mostly investigated in zebrafish and the frog Xenopus laevis, an amphibian model extensively used to study TH signalling.

A practical approach towards the evaluation of aberrant thyroid function tests

Objective: To provide insight in patterns and causes of aberrant thyroid function tests (TFT) and to propose a practical approach for clinicians.Methods: Starting from an illustrative case report, an extensive literature search was performed, resulting in a narrative literature review.Results: TFT that cannot be explained by the negative feedback principle of the hypothalamo-pituitary-thyroid axis are a challenge for every clinician. Various alternative explanations for these TFT should be considered before drawing the conclusion of thyroid disorder, since incorrect diagnosis and treatment can have severe consequences for the patient.For example, the combination of elevated or normal TSH with elevated free T4 or T3 levels may result from the use of certain drugs or lab interference, while low or normal TSH with low T3 or T4 can often be explained by non-thyroidal illness or central hypothyroidism due to pituitary failure. Correct identification of these clinical situations requires understanding thyroid hormone metabolism and action, knowledge of some laboratory techniques, and a multistep evaluation process.Conclusion: To avoid incorrect diagnosis and thus treatment, clinicians should be aware of the existence of aberrant TFT and know how to decipher them.

Neonatal Thyroid Function and Disorders

Thyroid hormone is essential for normal fetal brain development in utero and for the first 2 years of life. The developing fetus is initially reliant upon maternal thyroid hormones that cross the placenta, until the fetal thyroid begins to supply thyroid hormone for the fetus. Maternal thyroid status affects fetal thyroid function and maternal thyroid dysfunction can have a significant impact on the fetus and neonate. There are also several neonatal factors that can influence thyroid function. Here, we describe thyroid function in the fetus and neonate and discuss the most common thyroid disorders seen in neonates.

A rare cause of subclinical hypothyroidism: macro-thyroid-stimulating hormone

Background Subclinical hypothyroidism is a situation in which the thyroid-stimulating hormone (TSH) value exceeds the upper limit of normal, but the free triiodothyronine (T3) and thyroxine (T4) values are within the normal range. The etiology is similar to overt hypothyroidism. Case presentation An 18-year-old female patient was referred to our endocrinology clinic due to elevated TSH levels detected during a routine examination. She was clinically euthyroid and had a normal thyroid ultrasound pattern. The TSH concentration was measured twice independently, giving values of 5.65 μIU/mL and 5.47 μIU/mL. The polyethylene glycol (PEG) method for TSH measurement was used to determine the concentration of macro-TSH (m-TSH), a macromolecule formed between TSH and immunoglobulin (Ig). Using the same blood samples for which the TSH levels were found to be high, the PEG method found TSH levels to be within a normal range, with values of 1.50 μIU/mL (5.65-1.50 μIU/mL measured; a decrease of 75%) and 1.26 μIU/mL (5.47-1.26 μIU/mL measured; a decrease of 77%), respectively. The TSH values determined by the PEG precipitation test were markedly low, with PEG-precipitable TSH ratios greater than 75%. Conclusions The cause of 55% of subclinical hypothyroidism is chronic autoimmune thyroiditis. However, it is necessary to exclude other TSH-elevated conditions for diagnosis. One of these conditions is m-TSH, which should be kept in mind even though it is rarely seen. m-TSH should be considered especially in patients who have a TSH value above 10 μIU/mL without hypothyroidism symptoms or who require a higher levothyroxine replacement dose than expected to make them euthyroid.

To Treat or Not to Treat Subclinical Hypothyroidism, What Is the Evidence?

OBJECTIVE

levothyroxine prescriptions have increased remarkably during the last decade, and it is most likely to be prescribed in subclinical hypothyroidism. The aim of this review was to present data on when levothyroxine treatment should be initiated, and the effects of treatment in subclinical hypothyroidism on symptoms such as weight, quality of life, vitality, cognition, and cardiovascular disease. We also discuss evidence for different thyroid-hormone medications. In addition, the option to withhold medication when there is uncertain diagnosis or lack of clinical improvement is discussed.

METHODS

a literature search in PubMed on the term "treatment of subclinical hypothyroidism" in combination with "quality of life", "weight", "cognition", and "cerebrovascular disease".

RESULTS

current research supports that levothyroxine should be initiated in patients with a thyroid stimulating hormone (TSH) >10 mIU/L. Treatment for hypothyroidism is becoming more frequent. Symptoms related to vitality, weight, and quality of life in subclinical disease often persist with levothyroxine treatment, and other causes should be explored. Patients with cardiovascular-risk factors may benefit from treatment, especially younger patients. Caution is necessary when treating elderly subjects with levothyroxine.

CONCLUSION

lifelong treatment with levothyroxine should normally only be considered in manifest hypothyroidism. However, in subclinical hypothyroidism with a TSH >10 mIU/L, therapy is indicated. In milder subclinical forms, a wait-and-see strategy is advocated to see if normalization occurs. Subgroups with cardiovascular risk and subclinical hypothyroidism may benefit from levothyroxine therapy.

The Differential Diagnosis of Discrepant Thyroid Function Tests: Insistent Pitfalls and Updated Flow-Chart Based on a Long-Standing Experience

Background: Discrepant thyroid function tests (TFTs) are typical of inappropriate secretion of TSH (IST), a rare entity encompassing TSH-secreting adenomas (TSHoma) and Resistance to Thyroid Hormone (RTHβ) due to THRB mutations. The differential diagnosis remains a clinical challenge in most of the cases. The objective of this study was to share our experience with patients presenting with discrepant TFTs outlining the main pitfalls in the differential diagnosis. Methods: medical records of 100 subjects with discrepant TFTs referred to Thyroid Endocrine Centers at the University of Milan were analyzed, retrospectively. Patients were studied by dynamic testing (TRH test, T3-suppression test, or a short course of long-acting somatostatin analog, when appropriate), THRB sequencing, and pituitary imaging. Results: 88 patients were correctly diagnosed as RTHβ with (n = 59; 16 men, 43 women) or without THRB variants (n = 6; 2 men, 4 female) or TSHoma (n = 23; 9 men, 14 women). We identified 14 representative subjects with an atypical presentation or who were misdiagnosed. Seven patients, with spurious hyperthyroxinemia due to assays interference were erroneously classified as RTHβ (n = 4) or TSHoma (n = 3). Three patients with genuine TSHomas were classified as laboratory artifact (n = 2) or RTHβ (n = 1). Two TSHomas presented atypically due to coexistent primary thyroid diseases. In one RTHβ a drug-induced thyroid dysfunction was primarily assumed. These patients experienced a mean diagnostic delay of 26 ± 14 months. Analysis of the investigations which can differentiate between TSHoma and RTHβ showed highest accuracy for the T3-suppression test (100% specificity with a cut-off of TSH <0.11 μUI/ml). Pituitary MRI was negative in 6/26 TSHomas, while 11/45 RTHβ patients had small pituitary lesions, leading to unnecessary surgery in one case. Conclusions: Diagnostic delay and inappropriate treatments still occur in too many cases with discrepant TFTs suggestive of central hyperthyroidism. The insistent pitfalls lead to a significant waste of resources. We propose a revised flow-chart for the differential diagnosis.

Progress in the Pathogenesis, Diagnosis, and Treatment of TSH-Secreting Pituitary Neuroendocrine Tumor

TSH-secreting pituitary neuroendocrine tumor (PitNET) is one of the causes of central hyperthyroidism. The incidence of TSH PitNET is far lower than that of other PitNETs. The clinical manifestations of TSH PitNETs mainly include thyrotoxicosis or thyroid goiter, secretion disorders of other anterior pituitary hormones, and mass effect on the pituitary gland and its surrounding tissues. The application of high-sensitivity TSH detection methods contributes to the early diagnosis and timely treatment of TSH PitNETs. Improvements in magnetic resonance imaging (MRI) have advanced the noninvasive visualization of smaller PitNETs. Treatments for TSH PitNETs include surgery, drugs, and radiotherapy. This review focuses on the progress in pathogenesis, diagnosis, and treatment of TSH PitNETs to provide more information for the clinician.

Pesticides With Potential Thyroid Hormone-Disrupting Effects: A Review of Recent Data

Plant Protection Products, more commonly referred to as pesticides and biocides, are used to control a wide range of yield-reducing pests including insects, fungi, nematodes, and weeds. Concern has been raised that some pesticides may act as endocrine disrupting chemicals (EDCs) with the potential to interfere with the hormone systems of non-target invertebrates and vertebrates, including humans. EDCs act at low doses and particularly vulnerable periods of exposure include pre- and perinatal development. Of critical concern is the number of pesticides with the potential to interfere with the developing nervous system and brain, notably with thyroid hormone signaling. Across vertebrates, thyroid hormone orchestrates metamorphosis, brain development, and metabolism. Pesticide action on thyroid homeostasis can involve interference with TH production and its control, displacement from distributor proteins and liver metabolism. Here we focused on thyroid endpoints for each of the different classes of pesticides reviewing epidemiological and experimental studies carried out both in in vivo and in vitro. We conclude first, that many pesticides were placed on the market with insufficient testing, other than acute or chronic toxicity, and second, that thyroid-specific endpoints for neurodevelopmental effects and mixture assessment are largely absent from regulatory directives.

Levothyroxine Replacement in Obese Adults: The Role of Metabolic Variables and Aging on Thyroid Testing Abnormalities

CONTEXT

General rates of over- and underreplacement in levothyroxine (LT4) users with primary hypothyroidism are variably high. No information on LT4 adequacy exists in obesity.

OBJECTIVE

We explored rates and factors relating to LT4 adequacy in obese patients with primary hypothyroidism.

SETTING

Tertiary care center.

DESIGN

Among 4954 consecutive obese patients admitted between 2011 and 2014, 691 hypothyroid patients receiving LT4 therapy and 691 body mass index (BMI)-, age-, and sex-matched euthyroid controls underwent analysis of thyroid function, glucolipid profile, body composition, and indirect calorimetry. LT4 users were classified into low TSH (<0.27 mU/L), euthyroid (0.27 to 4.2 mU/L), and high TSH (>4.2 mU/L).

RESULTS

LT4 users constituted 13.9% of the incident population. TSH was low in 7.5%, high in 17.2%, and normal in 75.2% of LT4 users. Overtreatment decreased with aging and more LT4 users ≥65 years of age had normal TSH than those <65 years of age (P < 0.05). Compared with the euthyroid obese group, LT4 users showed higher adiposity, similar insulin resistance, but a healthier lipid profile. In multivariable analyses, LT4 dose was predicted by fat-free mass, hypothyroidism cause, and sex (P < 0.0001 to < 0.05). Risk of LT4 overreplacement increased with younger age (OR 0.96; 95% CI 0.94 to 0.99), higher LT4 dose (OR 2.98; 95% CI 1.44 to 6.14), and lower BMI (OR 0.93; 95% CI 0.88 to 0.99). Male sex increased the likelihood of LT4 underreplacement (OR 2.37; 95% CI 1.10 to 5.11).

CONCLUSIONS

Obesity is associated with milder rates of inadequate LT4 treatment compared with nonobese populations. LT4 adequacy increases with aging. Age, body composition, and sex are main determinants of LT4 requirements in obesity.

A 2019 update on TSH-secreting pituitary adenomas

Thyrotropin-secreting pituitary adenomas (TSH-omas) present with signs and symptoms of hyperthyroidism and they are characterized by elevated serum levels of free thyroid hormones with measurable TSH levels. TSH-omas are very infrequent, accounting for less than 1% of all pituitary adenomas, thus representing a very rare cause of hyperthyroidism. For this reason, data collected on these rare disorders are relatively few, but some new researches shed new light on the etiopathogenesis, the diagnosis and the treatment of such a remarkable disease. Since the same biochemical picture is present in the syndromes of thyroid hormone resistance (RTH), in particular in the form of pituitary RTH, failure in distinguishing these clinical entities may lead to improper patient management. Conversely, early diagnosis and correct treatment of TSH-omas may prevent the occurrence of neurological and endocrinological complications, thus leading to a better rate of cure. In the present short review article, the most relevant recent advances in the pathophysiology of TSH-omas are described.

Diagnosis and treatment of hypothyroidism in old people : A new old challenge

PURPOSE

To review the diagnosis and the treatment of both subclinical and overt hypothyroidism in old people, which could represent a challenge for the clinicians.

METHODS

Narrative literature review. An extensive literature search was performed using the databases of Scopus, Medline through PubMed, and Google Scholar from January 1975 to May 2019. The search terms were "hypothyroidism," "older adults," "elderly," and "myxedema."

RESULTS

Hypothyroidism is more common among older subjects in comparison to the younger counterparts. The hypothalamic-pituitary-thyroid axis and its hormones undergo significant changes due to the physiological aging process. For a correct diagnosis of hypothyroidism in old people clinicians must take such age-related changes into account.

CONCLUSIONS

The administration of replacement therapy in older adults should consider frailty, polypharmacy and a high risk to develop overtreatment symptoms. On the other hand, older patients with untreated or undertreated hypothyroidism may develop a state of myxedema coma.