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Primary congenital hypothyroidism is easily diagnosed on the basis of elevated plasma levels of thyroid-stimulating hormone (TSH). In contrast, in the rare disorders of thyroid hormone resistance, TSH and, in mild cases, also thyroid hormone levels are within the normal range. Thyroid hormone resistance is caused by defects in hormone metabolism, transport, or receptor activation and can have the same serious consequences for child development as congenital hypothyroidism. A total of n = 23,522 data points from a large cohort of children and young adults were used to generate normal values and sex-specific percentiles for the ratio of free triiodothyronine (T3) to free thyroxine (T4), the fT3/fT4 ratio. The aim was to determine whether individuals with developmental delay and genetically confirmed thyroid hormone resistance, carrying defects in Monocarboxylate Transporter 8 (MCT8), Thyroid Hormone Receptor alpha (THRα), and Selenocysteine Insertion Sequence-Binding Protein 2 (SECISBP2), had abnormal fT3/fT4 ratios. Indeed, we were able to demonstrate a clear separation of patient values for the fT3/fT4 ratio from normal and pathological controls (e.g., children with severe cerebral palsy). We therefore recommend using the fT3/fT4 ratio as a readily available screening parameter in children with developmental delay for the identification of thyroid hormone resistance syndromes. The fT3/fT4 ratio can be easily plotted on centile charts using our free online tool, which accepts various SI and non-SI units for fT3, fT4, and TSH.

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Objectives: In recent years, the free triiodothyronine/free thyroxine (FT3/FT4) ratio, a new comprehensive index for evaluating thyroid function, which could reflect thyroid function more stably and truly than serum thyroid hormone level, has been demonstrated to correlate with the risks of diabetes and cardiovascular disease in euthyroid adults. However, the correlation between thyroid hormone sensitivity and long-term prognosis in euthyroid patients with acute coronary syndrome (ACS) and diabetes after percutaneous coronary intervention (PCI) remains unclear. Methods: A total of 1,786 euthyroid patients with ACS who successfully underwent PCI at Beijing Anzhen Hospital from August 2021 to April 2022 were included in our study, which was divided into three groups according to tertiles of thyroid hormone sensitivity index. Cox regression, Kaplan-Meier, and receiver operating characteristic analyses were applied to analyze the associations between the FT3/FT4 ratio with ACS and diabetes after PCI. Results: Our analysis indicated that a lower level of FT3/FT4 ratio in euthyroid patients with acute coronary syndrome (ACS) and diabetes after PCI showed significantly higher incidences of major adverse cardiac and cerebrovascular events (MACCE) when compared with a higher level of FT3/FT4 ratio. After adjusting for other covariates, patients with a lower level of FT3/FT4 ratio were negatively associated with the risk of MACCE than those with a higher level of FT3/FT4 ratio (adjusted OR =1.61, 95% CI 1.05-2.47, P = 0.028). In subgroup analyses, individuals were stratified by age, sex, BMI, ACS type, hypertension, and dyslipidemia, showing that there were no significant interactions between the FT3/FT4 ratio and all subgroups for MACCE. In addition, the FT3/FT4 ratio performed better on ROC analyses for cardiac death prediction [area under the curve (AUC), 0.738]. Conclusion: A reduced level of FT3/FT4 ratio was a potential marker of poor prognosis in euthyroid patients with ACS and diabetes after PCI.

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Objective: Although several studies have examined the relationship between thyroid function and muscle strength, their population primarily derived from Asian areas, and their results were controversial. Thus, this study aimed to explore the association between thyroid function and handgrip strength (HGS) in the U.S. population. Methods: A total of 1,067 participants from NHANES were categorized into three different age groups including young (<45 years), middle (45~64 years), and old (≥65 years) age groups. Thyroid function was measured by the competitive binding immune-enzymatic assays, while HGS was examined by a trained evaluator using a dynamometer. The weighted multiple linear regression models were used to examine the association between thyroid function and handgrip strength. The restricted cubic splines were employed to explore the non-linear relationship between these two variables. All statistical analyses were performed using the SPSS version 20.0 and R software. Results: After adjustment for potential covariates, FT3/FT4, but not TSH was positively associated with HGS in middle age group (ß=0.091, t=2.428, P=0.016). The subgroup analysis by sex revealed that the positive association between FT3/FT4 and HGS was observed in the middle age group for both male and female participants (ß=0.163, t=2.121, P=0.035; ß=0.157, t=2.180, P=0.031). The RCS analysis showed a statistically significant non-linear association between FT3/FT4 and HGS in overall population (P for non-linear=0.026). After adjustment for covariates, men with low HGS had a significant lower FT3/FT4 than those without low HGS in old age group (P=0.013). There was a significant increase in TSH level for female participants with low HGS in old age group compared to those with normal HGS (P=0.048). Conclusions: This study demonstrated FT3/FT4, but not TSH, was positively associated with HGS in middle age group, and the different association was observed in men in middle age group when participants were stratified by sex. Future longitudinal cohort study should be conducted to reveal the causal relationship between thyroid function and muscle strength.

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AIM: To assess the effects of thyroid hormones on appendicular skeletal muscle index (SMI) and hand grip strength (HGS) in people with diabetes. METHODS: This cross-sectional cohort included 1,135 participants with diabetes admitted to 3 hospitals in Japan. Multiple regression analysis was performed to determine the associations among thyroid hormone levels, SMI, and HGS. RESULTS: Of the 1,135 participants, 480 were female. Their median (interquartile range) age, body mass index, durations of diabetes, and glycated haemoglobin levels were 68 years, 24.3 kg/m2, 10 years, and 7.6 %, respectively. The median (interquartile range) SMI (kg/m2) and hand grip strength of the cohort were 7.1 kg/m2 and 28.2 kg, respectively. Positive correlations between FT3 and the FT3/FT4 ratio with SMI and HGS was observed after adjusting for covariates in males. A negative correlation was found between the FT3/FT4 ratio and sarcopenia as a result of low SMI and low HGS in the male participants but not in females (p for interaction = 0.02). CONCLUSIONS: FT3/FT4 ratios may impact skeletal muscles in people with diabetes-particularly in males. Assessments of FT3/FT4 ratios may represent key indicators of muscle mass and strength in males.

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CONTEXT: It is still not clear how the free triiodothyronine (FT3) to free thyroxine (FT4) ratio affects the prognosis of acute myocardial infarction (AMI), especially the risk of heart failure (HF) subsequent to AMI. OBJECTIVE: The purpose of this study was to see how peripheral sensitivity to thyroid hormones, as measured by the FT3/FT4 ratio, affected HF and mortality after AMI. METHODS: Our study was a retrospective cohort study. The primary endpoint was HF after AMI during and after hospitalization. The secondary endpoints were all-cause death and cardiovascular death after hospitalization. RESULTS: The main sample included 3648 inpatients with AMI with a median age of 61.0 years; 68.9% were male. In the fully adjusted model, compared with patients in the lowest Q1 of the FT3/FT4 ratio, the risk of in-hospital HF in the highest Q4 patients was reduced by 44% (OR 0.56, 95% CI 0.44-0.72, P trend < .001), the risk of out-of-hospital HF was reduced by 37% (HR 0.63, 95% CI 0.48-0.84, P trend < .001), and the risks of all-cause and cardiovascular death were also significantly reduced. The analysis of different subgroups is consistent with the overall results. Furthermore, the sensitivity analysis of the euthyroid sample of 2484 patients was consistent with the main sample. Mediation analysis showed that altered levels of amino-terminal pro-B-type natriuretic peptide were mediators between the FT3/FT4 ratio and all endpoints in our study. CONCLUSION: The thyroid hormone peripheral sensitivity of the FT3/FT4 ratio is an independent predictor of HF and mortality after AMI.

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Introduction: Thyroid function has a large impact on humans' metabolism and is affected by iodine levels, but there is a scarcity of studies that elucidate the association between thyroid function and other elements. Methods: We performed a cross-sectional study on 1,067 adults to evaluate the associations of the common essential metals with thyroid function in adults living in an iodine-adequate area of China. Serum free thyroxine (FT4), free triiodothyronine (FT3), thyroid stimulating hormone (TSH), and blood metals (zinc, iron, copper, magnesium, manganese, and calcium) were measured. Further, the thyroid hormone sensitivity indexes, FT3:FT4 ratio, and thyrotropin T4 resistance index (TT4RI) were calculated. Linear regression, quantile g-computation, and Bayesian kernel machine regression methods were used to explore the association of metals with thyroid function. Results: We found that the TSH levels correlated with copper (negative) and zinc (positive). Iron and copper were positively associated with FT3 and FT4 levels, respectively. Iron (positive) and copper (negative) were correlated with the FT3:FT4 ratio. Furthermore, we found that manganese was inversely correlated with TT4RI, while zinc was positively correlated. Discussion: Our findings suggest that manganese, iron, copper, and zinc levels were strongly correlated with thyroid function, and patients with thyroid disorders are recommended to measure those metals levels.

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CONTEXT: Impaired sensitivity to thyroid hormones has been demonstrated to be positively associated with the prevalence of metabolic disorders. However, the relationship between sensitivity to thyroid hormones and metabolic dysfunction-associated fatty liver disease (MAFLD) and liver fibrosis remained unclear. OBJECTIVE: We aimed to determine the associations of thyroid hormone sensitivity indices with MAFLD and its progression to liver fibrosis in Chinese euthyroid adults. METHODS: This community-based study included 7906 euthyroid adults. We calculated the thyroid sensitivity indices, including free triiodothyronine to free thyroxine (FT3/FT4) ratio, Thyroid Feedback Quantile-based Index by FT4 (TFQIFT4), and Thyroid Feedback Quantile-based Index by FT3 (TFQIFT3), indicating peripheral and central thyroid hormone sensitivity respectively. Liver steatosis and fibrosis were diagnosed by vibration-controlled transient elastography (VCTE). Multivariable logistic/linear regression and restricted cubic spline (RCS) analysis were conducted. RESULTS: Compared with participants in the first quartile (Q1), the prevalence of MAFLD was increased by 62% in the fourth quartile (Q4) of FT3/FT4 ratio (OR 1.62; 95% CI [1.38, 1.91]) and by 40% in Q4 of TFQIFT3 (OR 1.40; 95% CI [1.18, 1.65]) (both P < .05). No associations between TFQIFT4 and the prevalence of MAFLD were found. In addition, compared with participants in Q1, the prevalence of liver fibrosis was increased by 45% in Q4 of TFQIFT3 (OR 1.45; 95% CI [1.03, 2.06]) (P < .05) in participants with MAFLD. CONCLUSION: Impaired central sensitivity to FT3 was associated with MAFLD and its progression to liver fibrosis. More prospective and mechanism studies are warranted to confirm these conclusions.

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Background: Crescent formation indicates severe glomerular pathology, and hypothyroidism usually predicts poor prognosis for severe diseases. However, the relationship between thyroid function and the progression of chronic kidney disease (CKD) is unclear. This study analysed the prognostic predictive value of the serum free triiodothyronine (FT3) to free thyroxine (FT4) ratio and its correlation with renal function in patients with CKD with crescent formation. Methods: This single-centre study included 162 CKD patients with glomerular crescents confirmed by renal pathology between March 2012 and December 2014. According to the first tertile (0.284) of FT3/FT4 ratio, the patients were divided into high and low FT3/FT4 ratio groups. Kaplan-Meier and Cox regression analyses were performed to evaluate the prognostic value of the FT3/FT4 ratio. Results: The age, haemoglobin, eGFR, urinary albumin-to-creatinine ratio, cardiac troponin T, N-terminal brain natriuretic peptide precursor, FT3, FT4, percentage of total crescents in non-globally sclerotic glomeruli, prevalences of hypertension, moderate to severe renal tubulopathy and crescentic nephritis, and proportion of patients receiving glucocorticoids and immunosuppressants were significantly different between high and low FT3/FT4 ratio groups (P < 0.05). Multivariate Cox regression analysis showed that when compared with patients with a high FT3/FT4 ratio (>0.284), those with intermediate and low FT3/FT4 ratios (≤0.284) had an increased risk of the long-term composite endpoint (P < 0.05 for various adjustment models). Conclusions: A low FT3/FT4 ratio is associated with increased mortality and worse outcome risk in CKD patients with crescent pathology.

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Background: Thyroid hormones play a vital role in maintaining the homeostasis of the cardiovascular system. The FT3/FT4 ratio can be used to evaluate the rate of T4-to-T3 conversion, reflecting the peripheral sensitivity of thyroid hormones. There is no study to investigate its relationship with death and cardiovascular disease (CVD) in the general population. Methods: This retrospective cohort study involved 8,018 participants with measured thyroid function and no prior thyroid disease who participated in the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2012. Mortality status was determined by routine follow-up using the National Death Index through December 31, 2015. Results: During a median of 87 months of follow-up, we observed 699 all-cause deaths, including 116 cardiovascular deaths. In multivariate adjusted models, higher free thyroxine (FT4) was linked to increased all-cause mortality (HR, 1.15 per SD; 95% CI, 1.09-1.22), cardiovascular mortality (HR, 1.18 per SD; 95% CI, 1.01-1.39), and CVD risk (HR, 1.17 per SD; 95% CI, 1.08-1.27). Higher free triiodothyronine (FT3) was linked to decreased all-cause mortality (HR 0.81 per SD; 95% CI, 0.70-0.93). Higher FT3/FT4 ratio was linked to decreased all-cause mortality (HR, 0.77 per SD; 95% CI, 0.69-0.85), cardiovascular mortality (HR, 0.79 per SD; 95% CI, 0.62-1.00), and CVD risk (HR, 0.82 per SD; 95% CI, 0.74-0.92). The FT3/FT4 ratio stratified findings were broadly consistent with the overall results. Conclusions: FT3, FT4, and the FT3/FT4 ratio were all independent predictors of all-cause death. FT4 and the FT3/FT4 ratio, but not FT3, were independent predictors of cardiovascular mortality and CVD risk. Along with FT3 and FT4, we should pay equal attention to the FT3/FT4 ratio in the general population.

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CONTEXT: It remains unclear whether the thyroid system could regulate the atherogenic remnant cholesterol (RC) levels in euthyroid status. OBJECTIVE: We aimed to investigate the relationship between sensitivity to thyroid hormones and RC levels in Chinese euthyroid population. METHODS: This study included 18 766 euthyroid adults. High RC levels were defined as the upper quartile of RC levels. The thyroid hormone sensitivity indices, including thyroid feedback quantile-based index (TFQI), thyroid-stimulating hormone index (TSHI), thyrotrophic thyroxine resistance index (TT4RI), and free triiodothyronine to free thyroxine (FT3/FT4) ratio were calculated. Linear and binary logistic regression analysis were applied to determine the associations between those composite indices with RC levels by genders. RESULTS: Both females and males with high RC levels exhibited co-existing higher TSH and FT4 levels. Linear regression analysis revealed that TFQI, TSHI, and TT4RI were positively, while FT3/FT4 ratio levels were negatively associated with serum RC levels. The odds ratios (ORs) (95% CI) for high RC levels were increased with rising TFQI quartiles (Q) [females: Q3 1.41 (1.22-1.63), Q4 1.61 (1.39-1.86); males: Q3 1.25 (1.09-1.45), Q4 1.38 (1.19-1.59), all P for trend < 0.001] after full adjustment, with Q1 as the reference. TSHI and TT4RI yielded similar results. By contrast, the ORs (95% CI) for high RC levels were decreased with increasing FT3/FT4 ratio quartiles in both genders (P for trend < 0.001). CONCLUSION: In euthyroid adults, reduced sensitivity to thyroid hormones was associated with high RC levels. Our results suggested an additive cardiometabolic risk of euthyroid population with thyroid hormones insensitivity.

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Thyroglobulin gene abnormalities cause thyroid dyshormonogenesis. A 6-yr-old boy of consanguineous parents presented with a large goiter and mild hypothyroidism (thyroid-stimulating hormone [TSH] 7.2 µIU/mL, free T3 [FT3] 3.4 pg/mL, free T4 [FT4] 0.6 ng/dL). Despite levothyroxine (LT4) administration and normal TSH levels, the goiter progressed slowly and increased rapidly in size at the onset of puberty. Thyroid scintigraphy revealed a remarkably high 123I uptake of 75.2%, with a serum thyroglobulin level of 13 ng/ml, which was disproportionately low for the goiter size. DNA sequencing revealed a novel homozygous missense variant, c.434G>A [p.Gly145Glu], in the thyroglobulin gene. Goiter growth was suppressed by increasing the LT4 dose. Thyroidectomy was performed at 17-yr-of-age. Thyroglobulin analysis of the thyroid tissue detected mutant thyroglobulin present in the endoplasmic reticulum, demonstrating that thyroglobulin transport from the endoplasmic reticulum to the Golgi apparatus was impaired by the Gly145Glu variant. During the clinical course, an elevated FT3/FT4 ratio was observed along with thyroid enlargement. A high FT3/FT4 ratio and goiter seemed to be compensatory responses to impaired hormone synthesis. Thyroglobulin defects with goiter should be treated with LT4, even if TSH levels are normal.

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BACKGROUND: Studies have demonstrated the associations between pre-pregnancy obesity, thyroid dysfunction, dyslipidemia, and increased risk of gestational diabetes mellitus (GDM) in pregnant women. This study was designed to investigate whether and to what extent, the interactions between these factors contribute to the risk of GDM. METHODS: A case-control study of 232 GDM cases and 696 controls was conducted among pregnant women from Hangzhou, China. Multiple logistic regression analysis was applied to identify independent risk factors of GDM. Crossover analysis was performed to assess the interactive effects of pre-pregnancy body mass index (pBMI), thyroid hormones, and blood lipid profiles on the risk of GDM. The indexes including attributable proportion (AP) to the interaction and the relative excess risk due to interaction (RERI) were calculated. RESULTS: Chinese pregnant women with pBMI > 23 kg/m2 (adjusted: OR = 4.162, p < 0.001), high triglyceride levels (> 2.30 mmol/L) (adjusted: OR = 1.735, p < 0.001), and the free triiodothyronine/free thyroxine (FT3/FT4) ratio ≥ 0.502 (OR = 4.162, p < 0.001) have significantly increased risk of GDM. Crossover analysis indicated that there were significant interactions between pre-pregnancy overweight/obesity and FT3/FT4 ≥ 0.502 (AP = 0.550, p < 0.001; RERI = 7.586, p = 0.009), high TG levels and FT3/FT4 ≥ 0.502 (AP = 0.348, 95%CI = 0.081-0.614, P = 0.010; RERI = 2.021, 95%CI = 0.064-3.978, p = 0.043) on the risk of GDM. CONCLUSION: The interactions between pBMI and FT3/FT4 ratio, TG level and FT3/FT4 ratio may have significant impacts on the risk of GDM in pregnant women. Such findings may help improve our understanding of the pathogenesis of GDM as well as develop comprehensive strategies for the management of GDM.

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Aims: Abnormal thyroid hormone secretions can alter the manifestation and prognosis of cardiovascular disease. To assess the effect of the free triiodothyronine (FT3)/free thyroxine (FT4) ratio on the prognosis of patients with heart failure (HF), we performed a propensity-matched study on patients with well-balanced baseline characteristics. Methods: Overall, 8,887 patients with HF were divided into two groups according to the FT3/FT4 ratio. Propensity scores were calculated from each patient. A cohort comprising 2,164 pairs with high or low ratios and with 34 well-balanced baseline characteristics was then assembled. The endpoints were Cardiovascular (CV) mortality and all-cause mortality. The correlation between FT3/FT4 ratio and prognosis was assessed using matched Cox regression analyses. The mean follow-up was 3.3 years. Results: In the full pre-match cohort, 3,710 (41.7%) patients died, with 2,581 (29.0%) cases of CV mortality. In the matched-pair cohort, all-cause mortality occurred in 923 (1,238/10,000 person-years of follow-up) patients with a high ratio and 1,036 (1,484/10,000 person-years) patients with a low ratio, resulting in a matched HR of 0.841 (95% CI: 0.769-0.919; P < 0.001). For CV mortality, the result was 638 (856/10,000 person-years) and 714 (1,023/10,000 person-years) patients, respectively, resulting in a matched HR of 0.844 (95% CI: 0.759-0.940; P < 0.001). Subgroup analysis revealed that a low FT3/FT4 ratio had a greater predictive value for all-cause and CV mortality in elderly or male patients and in patients with coronary artery disease (CAD), hypertension, diabetes mellitus, HFmrEF, or HFpEF. Conclusions: A low FT3/FT4 ratio is valuable for predicting CV mortality and all-cause mortality in patients with HF.

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PURPOSE: Free triiodothyronine (FT3) and FT3/free thyroxine (FT4) ratio have been associated with mortality in various diseases. However, no study to date has identified a link between FT3, FT3/FT4 ratio and all-cause mortality in patients with diabetic foot ulcers (DFUs). This study aimed to investigate this relationship. METHODS: This retrospective cohort study included 726 patients diagnosed with DFUs in a public hospital from January 2015 to October 2019. Patients were classified by the optimal cut-off values of the FT3 and FT3/FT4 ratio, respectively. The association of FT3 and FT3/FT4 ratio with all-cause mortality was evaluated in a multivariable cox regression model. Directed acyclic graphs were used to assess the minimally sufficient sets of confounding variables. RESULTS: Log rank tests indicated that patients with low FT3 and FT3/FT4 ratio had lower overall survival rates (all p < 0.001). The adjusted HRs for all-cause mortality were 0.48 (95% CI: 0.32-0.73, P = 0.001) when comparing high versus low FT3 and 0.47 (95% CI: 0.32-0.70, P < 0.001) when comparing high versus low FT3/FT4 ratio. Subgroup analyses showed that these associations existed only in elderly patients (≥65 years) and women, after adjustment. In men, only high FT3/FT4 ratio was associated with low all-cause mortality, after adjustment. CONCLUSION: Routine assessment of FT3 and FT3/FT4 ratio may be a simple and effective way to identify high-risk patients with DFUs, especially in elderly patients and women.

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CONTEXT: Establishing the etiology of thyrotoxicosis is of utmost importance to plan the appropriate line of therapy. However, certain scenarios such as absence of pathognomonic clinical features of Graves' disease in some patients, or non-availability of radionuclide scanning and newer generation TRAb assays especially in resource-poor settings, necessitates utilization of other, simple and effective measures to differentiate between the two common causes of thyrotoxicosis, Graves' disease (GD) and Destructive thyroiditis (DT). AIMS: The aim of this work was to study the role of FT3/FT4 ratio, T3/T4 ratio and color flow Doppler ultrasound in treatment-naïve patients with thyrotoxicosis, in comparison to Tc-99m pertechnetate thyroid scanning in the differentiation of thyrotoxicosis due to GD and DT. MATERIALS AND METHODS: Clinical data was collected from all study subjects. Thyroid function tests including FT3, FT4, T3, T4 and TSH, TSH Receptor Antibody (TRAb), Technetium Tc 99m pertechnetate scan and the mean peak systolic velocity in inferior thyroid artery (mean PSV-ITA) by color Doppler ultrasonography of thyroid gland was done in all patients. RESULTS: A total of 83 treatment-naïve patients with thyrotoxicosis (61 with GD and 22 with DT) were studied. Mean PSV-ITA, T3/T4 ratio and FT3/FT4 ratio showed a sensitivity of 85.2%, 73.8%, and 77.04%, and a specificity of 90.9%, 72.7%, and 59.09%, respectively. The three parameters in combination yielded a positive predictive value of 100% in the diagnosis of Graves' disease. CONCLUSION: Results of this study show that inferior thyroid artery blood flow, T3/T4 ratio and FT3/FT4 ratio are useful parameters in the differentiation between GD and DT.

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Background: Thyroid function is closely involved in cardiovascular diseases. The free triiodothyronine (fT3) to free thyroxine (fT4) ratio has been reported as a risk factor for coronary artery disease, but its prognostic value in euthyroid patients with myocardial infarction with nonobstructive coronary arteries (MINOCA) remains unclear. Methods: A total of 1162 euthyroid patients with MINOCA were enrolled and divided according to decreased tertiles of fT3/fT4 ratio. The study endpoint was major adverse cardiovascular events (MACE), including all-cause death, nonfatal MI, nonfatal stroke, revascularization, and hospitalization for unstable angina or heart failure. Kaplan-Meier, Cox regression, and receiver-operating characteristic analyses were performed. Results: Patients with lower fT3/fT4 tertile levels had a significantly higher incidence of MACE (10.0%, 13.9%, 18.2%; p=0.005) over the median follow-up of 41.7 months. The risk of MACE increased with the decreasing fT3/fT4 tertiles even after multivariate adjustment (tertile1 as reference, tertile2: HR 1.58, 95% CI: 1.05-2.39, p=0.030; tertile3: HR 2.06, 95% CI: 1.17-3.11, p=0.006). Lower level of fT3/fT4 ratio remained a robust predictor of MACE in overall (HR 1.64, 95% CI: 1.18-2.29, p=0.003) and in subgroups. When adding fT3/fT4 ratio [area under the curve (AUC) 0.61] into the thrombolysis in myocardial infarction (TIMI) risk score (AUC 0.69), the combined model (AUC 0.74) yielded a significant improvement in discrimination for MACE (ΔAUC 0.05, p=0.023). Conclusions: Low level of fT3/fT4 ratio was strongly associated with a poor prognosis in euthyroid patients with MINOCA. Routine assessment of fT3/fT4 ratio may facilitate risk stratification in this specific population.

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Background: In euthyroid patients undergoing percutaneous coronary intervention (PCI), it is still unclear whether free triiodothyronine to free thyroxine (FT3/FT4) ratio can predict the recurrence of cardiovascular events (CVEs). We aim to investigate its association with recurrent long-term adverse events in this population. Methods: 3549 euthyroid patients with prior CVEs history undergoing PCI were consecutively enrolled in our study and subsequently divided into three FT3/FT4 ratio tertiles (T1<2.41, n=1170; 2.41≤T2<2.75, n=1198; T3>2.75, n=1181). The primary endpoint was major adverse cardiovascular and cerebrovascular event (MACCE), a composite of all-cause death, myocardial infarction, stroke and revascularization. The secondary endpoints were all-cause death and cardiac death. Results: The median follow-up time was 5 years. The incidence of all-cause death, cardiac death and MACCE were significantly higher among patients in the lowest FT3/FT4 tertile (P<0.05). After adjustment of confounding factors, decreased FT3/FT4 ratio was independently associated with an increased risk of all-cause death (HR 1.82, 95% CI 1.13-2.93, P=0.014), cardiac death (HR 1.90, 95% CI 1.04-3.46, P=0.036) and MACCE (HR 1.33, 95% CI 1.10-1.60, P=0.003) which was driven mainly by all-cause death. Conclusions: In euthyroid patients with prior cardiovascular events undergoing PCI, FT3/FT4 ratio might be a potential predictor of all-cause and cardiac mortality. Routine assessment of FT3/FT4 ratio might be a simple and effective tool for risk stratification in this specific patient population.

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INTRODUCTION: Insulin resistance (IR) is a key and early pathogenetic mechanism of cardiometabolic diseases with huge potential if detected early and mitigated, for lowering the burden of the disease. Available data are conflicting to what extent adult thyroid dysfunction is associated with IR. Therefore, we aimed to investigate the association and to identify which thyroid parameters are predictors of IR. MATERIAL AND METHODS: After undergoing basic anthropometric and biochemical studies including thyroid hormones, oral glucose tolerance test (OGTT), and insulin, 1425 middle-aged individuals were divided into three groups according to thyroid parameters: overt hypothyroidism (OH), subclinical hypothyroidism (SH), and euthyroidism (EU). RESULTS: The homeostasis model assessment of IR (HOMA-IR), fasting insulin, and two-hour glucose levels of OGTT showed a steady, yet insignificant, increase from EU through SH to OH. The strongest noted correlations were those of insulin levels with free triiodothyronine/free thyroxine (FT3/FT4) ratio (r = 0.206, p < 0.001) and FT3 (r = 0.205, p < 0.001). Also in the case of HOMA-IR, the only statistically significant correlations were observed for FT3 (r = 0.181, p < 0.001) and the FT3/FT4 ratio (r = 0.165, p < 0.001). Among other thyroid hormones, linear logistic regression proved the FT3/FT4 ratio as the only significant predictor of HOMA-IR (linear coefficient = 5.26, p = 0.027) and insulin levels (linear coefficient = 18.01, p = 0.023), respectively. Thyroid-stimulating hormone was not associated with IR in either correlation or regression analysis. CONCLUSIONS: The FT3/FT4 ratio should be more emphasised in the diagnosis and treatment of thyroid disorders. Patients could benefit from a pharmacological reduction of the FT3/FT4 ratio, potentially leading to a decrease in insulin resistance, and thus a corresponding decrease in the risk of the cardiometabolic diseases.

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BACKGROUND AND AIMS: Whether routine assessment of FT3/FT4 ratio in euthyroid patients with three-vessel disease (3VD) could help identify high-risk individuals remains unclear. This study evaluated the relationship between FT3/FT4 ratio and long-term clinical outcomes in this specific population. METHODS AND RESULTS: This study included 2106 euthyroid patients with 3VD (stenoses of ≥50% in right coronary artery, left circumflex and left anterior descending). Patients were categorized into three groups according to tertiles of FT3/FT4 ratio (Q1>2.58,n = 704; 2.2 ≤ Q2<2.58, n = 706; Q3<2.22, n = 696). The median follow-up time was 5.3 years, during which 206 deaths and 332 MACCEs (consisting of all-cause death, myocardial infarction, and stroke) occurred. Compared with the other two groups, patients with low level of FT3/FT4 ratio tended to be female, older, diabetic, and had significantly higher incidences of all-cause death, cardiac death and MACCE (all P < 0.05). Cox regression analysis showed that patients with low level of FT3/FT4 ratio had higher risks of long-term cardiac death (adjusted HR = 1.87, 95% CI 1.06-3.28, P = 0.030) and MACCE (adjusted HR = 1.43, 95% CI 1.07-1.93, P = 0.017) than those with high level of FT3/FT4 ratio. Subgroup analysis showed there was a significant interaction between FT3/FT4 ratio and age (≥65 years vs.<65 years) for MACCE (P = 0.029). CONCLUSION: Low level of FT3/FT4 ratio is independently associated with an increased risk of long-term cardiac death and MACCE in euthyroid patients with 3VD. Routine assessment of FT3/FT4 ratio might be helpful to identify high-risk individuals in this specific population.

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INTRODUCTION: Graves' Disease (GD) is an autoimmune hyperthyroidism occurring mostly in young women. The main pathogenic role of the disease is attributed to TSH receptor antibodies (TRAb), which stimulate the thyroid gland to increase production of the most active thyroid hormone- triiodothyronine (T3). High level of TRAb and a large goiter size are commonly known as poor prognostic factors for the disease and are used to predict relapse. THE AIM: The purpose of our study was to check the correlation between fT3:fT4 ratio with TRAb concentration, total volume of thyroid and age of GD onset. MATERIALS AND METHODS: 114 patients with onset or relapse of GD were analyzed. Those after thyroidectomy or radioiodine therapy were not taken into analysis. The data was retrospectively retrieved from the hospital's records consisting of patients' sex, age, level of TRAb, fT3, fT4 and thyroid volume on ultrasonography. The association between fT3:fT4 and TRAb concentration, thyroid volume and age was evaluated using Pearson correlation coefficient. RESULTS: The group was predominated by women (19.3% men, 80.7% women). The average age was 47.0. The analysis revealed positive correlation between: 1) fT3:fT4 ratio and total volume of thyroid (correlation ratio: 0.37; p <0.05) 2) fT3:fT4 ratio and level of TRAb (correlation ratio: 0.26; p or <0.05) 3) negative correlation between fT3:fT4 ratio and patient's age (correlation ratio: -0.14; p = 0.144). CONCLUSIONS: Positive correlations between fT3:fT4 ratio and TRAb level and total volume of thyroid (poor predictors of GD) may confirm that high level of fT3 can also be a prognostic factor for GD severity.

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