Triiodothyronine

Background: Despite being the most performed laboratory endocrine investigation, the optimum use of thyroid tests (thyrotropin [TSH] and thyroid hormone [TH] measurement) is open to question and the interpretation of the results from these tests can be ambiguous. The American Thyroid Association (ATA) with its expertise support the endeavor of the U.S. Centers for Disease Control (CDC) and the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) to improve and maintain standardization and harmonization of thyroid testing. ATA mandated an international interdisciplinary working group panel to survey the status of thyroid testing by reviewing the recent literature to revise or update the criteria as needed in mutual agreement and to inform clinical care. Summary: This review represents the conclusions on the clinical use of current routine TSH and TH (thyroxine [T4] and triiodothyronine [T3]) assays, taking into account geographic differences in disease prevalence and clinical and laboratory practice among writing members. The interaction between physiological, pathophysiological, and pharmacological factors and thyroid assays can affect their measurements and confound result interpretation. These factors need to be considered in the clinical context of the patient for appropriate test ordering and result interpretation. Despite significant advances in laboratory methods over the past 50 years, routine thyroid assays remain susceptible to idiosyncratic analytical interference that may produce spurious results. Improved standardization needs to be demonstrated through ongoing international efforts before results from different assays can be considered equivalent. Emerging technology (e.g., mass spectrometry) shows promise for improved analytical performance, but more evidence of its clinical utility and improved throughput is required before it can be considered for routine use. Close clinical-laboratory collaboration is encouraged to overcome and avoid the pitfalls in thyroid testing as well as resolve clinically discrepant results. The evidence base supporting the conclusions of this review is summarized in four detailed online technical supplements. Conclusions: Over the past five decades, testing for TSH, T4, and T3 has evolved from manual radioisotopic immunoassays to nonisotopic multiplexed immunometric assays using highly automated equipment. Despite these technical advances, physicians and laboratorians performing these analyses must understand limitations of these methods to properly order tests and interpret results.

IntroductionStudies comparing levothyroxine (LT4) therapy with LT4 + liothyronine (LT3) or desiccated thyroid extract (DTE) did not detect consistent superiority of either treatment. Here, we investigated these therapies, focusing on the whole group of LT4-treated hypothyroid patients, while also exploring the most symptomatic patients.MethodologyProspective, randomized, double-blind, crossover study of 75 hypothyroid patients randomly allocated to 1 of 3 treatment arms, LT4, LT4 + LT3, and DTE, for 22 weeks. The primary outcomes were posttreatment scores on the 36-point thyroid symptom questionnaire (TSQ-36), 12-point quality of life general health questionnaire (GHQ-12), the Wechsler memory scale-version IV (VMS-IV), and the Beck Depression Inventory (BDI). Secondary endpoints included treatment preference, biochemical and metabolic parameters, etiology of hypothyroidism, and Thr92Ala-DIO2 gene polymorphism. Analyses were performed with a linear mixed model using subject as a random factor and group as a fixed effect.ResultsSerum TSH remained within reference range across all treatment arms. There were no differences for primary and secondary outcomes, except for a minor increase in heart rate caused by DTE. Treatment preference was not different and there were no interferences of the etiology of hypothyroidism or Thr92Ala-DIO2 gene polymorphism in the outcomes. Subgroup analyses of the 1/3 most symptomatic patients on LT4 revealed strong preference for treatment containing T3, which improved performance on TSQ-36, GHQ-12, BDI, and visual memory index (VMS-IV component).ConclusionsAs a group, outcomes were similar among hypothyroid patients taking DTE vs LT4 + T3 vs LT4. However, those patients that were most symptomatic on LT4 preferred and responded positively to therapy with LT4 + LT3 or DTE.

The elevated fluoride from drinking water impacts on T3, T4 and TSH hormones. The aim was study impacts of drinking water fluoride on T3, T4 and TSH hormones inYGA (Yazd Greater Area). In this case- control study 198 cases and 213 controls were selected. Fluoride was determined by the SPADNS Colorimetric Method. T3, T4 and TSH hormones tested in the Yazd central laboratory by RIA (Radio Immuno Assay) method. The average amount of TSH and T3 hormones based on the levels of fluoride in two concentration levels 0-0.29 and 0.3-0.5 (mg/L) was statistically significant (P = 0.001 for controls and P = 0.001 for cases). In multivariate regression logistic analysis, independent variable associated with Hypothyroidism were: gender (odds ratio: 2.5, CI 95%: 1.6-3.9), family history of thyroid disease (odds ratio: 2.7, CI 95%: 1.6-4.6), exercise (odds ratio: 5.34, CI 95%: 3.2-9), Diabetes (odds ratio: 3.7, CI 95%: 1.7-8), Hypertension (odds ratio: 3.2, CI 95%: 1.3-8.2), water consumption (odds ratio: 4, CI 95%: 1.2-14). It was found that fluoride has impacts on TSH, T3 hormones even in the standard concentration of less than 0.5 mg/L. Application of standard household water purification devices was recommended for hypothyroidism.

BackgroundGrowing evidence indicates that thyroid function plays a critical pathophysiological role in diabetic microvascular complications. Nevertheless, the specific association between thyroid hormones, particularly free triiodothyronine (fT3), and diabetic retinopathy (DR) remains controversial.MethodsAfter applying the inclusion and exclusion criteria, 3703 patients were included in the baseline analysis. Multivariate logistic regression models were employed to assess the cross-sectional association between baseline fT3 levels and both the prevalence of DR. Subsequently, 1476 patients who underwent follow-up fundus photography were eligible for the retrospective cohort study. This secondary analysis examined the relationship between baseline fT3 quartiles and the risk of DR onset or progression. Additionally, two-sample Mendelian randomization (MR) analysis was performed to analyze the causal effect of circulating fT3 on non-proliferative DR (NPDR) and proliferative DR (PDR).ResultsIn the cross-sectional analysis, higher fT3 levels were inversely associated with DR after multivariable adjustment, including NPDR (OR = 0.61, 95% CI: 0.50-0.74) and PDR (OR = 0.24, 95% CI: 0.13-0.44). In the longitudinal cohort, patients with moderate fT3 levels (Q2-Q3) had a lower risk of DR onset or progression versus the lowest quartile (Q1). This protective association remained significant in those with suboptimal glycemic control (HbA1c ≥7%) or longer diabetes duration (≥ 10 years), with risk reductions of 43% (Q2) and 37% (Q3) in the former, and 44% (Q2) and 49% (Q3) in the latter. Notably, among older patients (≥ 55 years), the benefit extended across Q2-Q4. Finally, the MR analysis suggested a potential protective effect of higher fT3 levels on NPDR (MR Egger, OR = 0.131, 95% CI: 0.023-0.755, P = 0.044).ConclusionIn conclusion, our study demonstrated an inverse association between fT3 levels and the risk of both NPDR and PDR. Moderate fT3 levels were associated with a lower risk of DR onset or progression, particularly among patients with suboptimal glycemic control (HbA1c ≥7%) or longer diabetes duration (≥ 10 years). In older patients (≥ 55years), even relatively higher fT3 levels may be protective. MR analysis suggested a potential protective effect of elevated fT3 levels on the risk of NPDR, which was significant only in the MR Egger model.