Measurement of Reverse Triiodothyronine Level and the Triiodothyronine to Reverse Triiodothyronine Ratio in Dried Blood Spot Samples at Birth May Facilitate Early Detection of Monocarboxylate Transporter 8 Deficiency

Background: Monocarboxylate transporter 8 (MCT8) deficiency is an X-chromosome-linked neurodevelopmental disorder resulting from impaired thyroid hormone transport across the cell membrane. The diagnosis of MCT8 deficiency is typically delayed owing to the late appearance of signs and symptoms as well as the inability of standard biomarkers of neonatal screening to provide early detection. In this study, we report, for the first time, the ability to detect MCT8 deficiency at birth using dried blood spot (DBS) samples. Methods: We retrospectively measured triiodothyronine (T3), thyroxine (T4), and reverse T3 (rT3) levels in DBS samples obtained at 4-5 days of life from 6 infants with genetically confirmed MCT8 deficiency and from 110 controls. The latter consisted of 58 healthy term neonates obtained at the same time, 16 were stored for more than 1 year before measurement to match samples from the MCT8-deficient infants. Ten DBS samples were collected at day 1 of life and 42 samples were from prematurely born neonates. Measurements were carried out in extract from eight millimeters diameter DBS using liquid chromatography-tandem mass spectrometry. Results: Contrary to characteristic iodothyronine abnormalities of MCT8 deficiency during later life, T3 and T4 values were not discriminatory from those of other study groups. In contrast, rT3 was significantly lower. The T3/rT3 ratio was higher in the DBS samples from the MCT8-deficient infants compared with all other groups with no overlap (p < 0.0001). Conclusions: rT3 and T3/rT3 ratio in DBS samples obtained from neonates can serve as biomarkers to detect MCT8 deficiency at birth.

Higher Caloric Exposure in Critically Ill Patients Transiently Accelerates Thyroid Hormone Activation

INTRODUCTION

The inflammatory response of critical illness is accompanied by nonthyroidal illness syndrome (NTIS). Feeding has been shown to attenuate this process, but this has not been explored prospectively over time in critically ill patients.

OBJECTIVE

To explore the impact of calorie exposure on NTIS over time in critically ill patients.

METHODS

Mechanically ventilated patients with systemic inflammatory response syndrome (SIRS) were randomized to receive either 100% or 40% of their estimated caloric needs (ECN). Thyroid hormones were measured daily for 7 days or until intensive care unit discharge or death. Mixed level regression modeling was used to explore the effect of randomization group on plasma triiodothyronine (T3), reverse triiodothyronine (rT3), thyroxine (T4), and thyroid stimulating hormone (TSH), as well as the T3/rT3 ratio.

RESULTS

Thirty-five participants (n=19 in 100% ECN; n=16 in 40% ECN) were recruited. Adjusting for group differences in baseline T3/rT3 ratio, the parameters defining the fitted curves (intercept, linear effect of study day, and quadratic effect of study day) differed by randomization group (P = 0.001, P = 0.01, and P = 0.02 respectively). Plots of the fitted curves revealed that participants in the 100% ECN group had a 54% higher T3/rT3 ratio on postintervention day 1 compared with the 40% ECN group, a difference which attenuated over time. This was driven by a 23% higher plasma T3 and 10% lower plasma rT3 levels on postintervention 1.

CONCLUSIONS

Higher caloric exposure in NTIS patients transiently attenuates the drop of the plasma T3/rT3 ratio, an effect that is minimized and finally lost over the following 3 days of continued higher caloric exposure.

Does Reverse Triiodothyronine Testing Have Clinical Utility? An Analysis of Practice Variation Based on Order Data from a National Reference Laboratory

BACKGROUND

Clinical laboratories are under pressure to increase value by improving test utilization. The clinical utility of reverse triiodothyronine (rT3) is controversial. A study was conducted to identify order patterns that might suggest inappropriate utilization of rT3.

METHODS

All orders for thyroid tests placed over a period of one year at a national reference laboratory were reviewed. Order patterns by client (hospital) and by provider were analyzed. A Pareto analysis was conducted to determine the percentage of orders placed as a function of the percentage of providers. A systematic review of the indexed literature and an informal review of the web were conducted to identify indications for rT3 testing.

RESULTS

There were 402,386 orders for 447,664 thyroid tests, including 91,767 orders for rT3. These orders were placed by 60,733 providers located at 1139 different organizations. Only 20% of providers who ordered thyroid tests placed an order for rT3. Of those who placed an order for rT3, 95% placed two orders or fewer for rT3. One hundred providers (0.1% of the 60,733 providers who placed orders for thyroid tests) accounted for 29.5% of the orders for rT3. Of the 100 providers, 60 with the highest order volumes for rT3 were classified as practitioners of functional medicine. A systematic review of Medline found little evidence to support the high volumes of orders for rT3. A survey of Web sites for functional medicine suggests that rT3 is useful for the diagnosis of rT3 dominance and can be used to direct triiodothyronine replacement therapy.

CONCLUSIONS

There is wide practice variation in rT3 testing. A high proportion of tests are ordered by a relatively small proportion of providers. There is little evidence to support high volumes of rT3 testing placed by some practitioners.

The Prognostic Value of Severe Malnutrition in the Development of Nonthyroidal Illness in Head and Neck Cancer Patients

BACKGROUND

Thyroid hormone metabolism is modulated by starvation and overfeeding but also by dietary composition. Unfortunately, little is known about the effect of malnutrition on disease-induced nonthyroidal illness (NTI). In this study, we investigated whether the degree of NTI after surgery differed between severely malnourished and well-fed patients with head and neck cancer.

METHODS

Plasma levels of the thyroid hormones 3',5-triiodothyronine (T(3)), reverse T(3) (rT(3)), free T(4) (FT(4)), and thyrotropin (TSH) were measured on the first day before the operation and on the first, fourth, and seventh day after the operation in 16 malnourished patients who were admitted for intentional curative surgery of T1-T4 carcinomas of the head and neck. Six well-fed head and neck cancer patients eligible for surgical treatment served as a control group.

RESULTS

In the malnourished group, rT(3) showed a significant increase, whereas T(3) and FT(4) decreased significantly due to the operation. TSH showed no significant change. During the postoperative course, it took 7 days until rT(3) and 4 days until T(3) and FT(4) were restored to their preoperative value. In contrast, well-fed patients did not develop NTI.

CONCLUSIONS

This study shows that peri- and postoperative rT(3), T(3), and FT(4) levels change significantly in malnourished patients compared with well-fed patients. Therefore, it can be concluded that nutrition status of patients undergoing major head and neck surgery should be optimized in order to prevent the development of NTI.

Serum Thyroid Function, Mortality and Disability in Advanced Old Age: The Newcastle 85+ Study

CONTEXT

Perturbations in thyroid function are common in older individuals but their significance in the very old is not fully understood.

OBJECTIVE

This study sought to determine whether thyroid hormone status and variation of thyroid hormones within the reference range correlated with mortality and disability in a cohort of 85-year-olds.

DESIGN

A cohort of 85-year-old individuals were assessed in their own homes (community or institutional care) for health status and thyroid function, and followed for mortality and disability for up to 9 years.

SETTING AND PARTICIPANTS

Six hundred and forty-three 85-year-olds registered with participating general practices in Newcastle and North Tyneside, United Kingdom.

MAIN OUTCOMES

All-cause mortality, cardiovascular mortality, and disability according to thyroid disease status and baseline thyroid hormone parameters (serum TSH, FT₄, FT₃, and rT₃). Models were adjusted for age, sex, education, body mass index, smoking, and disease count.

RESULTS

After adjustment for age and sex, all-cause mortality was associated with baseline serum rT₃ and FT₃ (both P < .001), but not FT₄ or TSH. After additional adjustment for potential confounders, only rT₃ remained significantly associated with mortality (P = .001). Baseline serum TSH and rT₃ predicted future disability trajectories in men and women, respectively.

CONCLUSIONS

Our study is reassuring that individuals age 85 y with both subclinical hypothyroidism and subclinical hyperthyroidism do not have a significantly worse survival over 9 years than their euthyroid peers. However, thyroid function tests did predict disability, with higher serum TSH levels predicting better outcomes. These data strengthen the argument for routine use of age-specific thyroid function reference ranges.

Permanent atrial fibrillation in heart failure patients as another condition with increased reverse triiodothyronine concentration

OBJECTIVE

To fully investigate the thyroid hormonal function in patients with the most common arrhythmia - atrial fibrillation.

MATERIALS AND METHODS

120 patients (aged 55-85 yrs) with symptoms of congestive heart failure exacerbation and no other concomitant disorders (inclusion criteria: normal cardiac troponin T at admission and 12 hours after, normal renal, hepatic and respiratory function; exclusion criteria: inflammatory state, history of myocardial infarction). Depending on the presence of permanent atrial fibrillation (PAF), patients were divided into two groups: PAF (34 females, 26 males) and regular sinus heart rhythm (43 females, 17 males), the groups did not differ in terms of heart rate, blood pressure, presence of overt/subclinical thyroid dysfunction, and medical therapy used. In all subjects thyroid stimulating hormone, free thyroxine, free triiodothyronine, reverse triiodothyronine were measured; echocardiography was performed.

RESULTS

PAF group showed higher FT4 and rT3 (1.41 vs. 1.27 ng/dl, p=0.0007; 0.61 vs. 0.32 ng/ml, p<0.0001, respectively). With ROC curve analysis the biochemical thyroid related factor of the highest prognostic value for PAF occurrence (with the highest sensitivity and specificity: 77% and 72%, respectively) was rT3 with the cut-off of above 0.3 ng/ml. Also, a positive correlation between rT3 levels and left ventricular posterior wall diameter was observed (Spearman's correlation coefficient 0.33, p=0.0093).

CONCLUSIONS

PAF is another condition where an increase in rT3 is observed. rT3 concentration above 0.3 ng/ml may be a novel biochemical sign associated with the presence of PAF in patients with chronic heart failure.

Relation of thyroid hormone abnormalities with subclinical inflammatory activity in patients with type 1 and type 2 diabetes mellitus

Thyroid hormone (TH) abnormalities are common in patients with diabetes mellitus (DM). These thyroid hormone abnormalities have been associated with inflammatory activity in several conditions but this link remains unclear in DM. We assessed the influence of subclinical inflammation in TH metabolism in euthyroid diabetic patients. Cross-sectional study involving 258 subjects divided in 4 groups: 70 patients with T2DM and 55 patients with T1DM and two control groups of 70 and 63 non-diabetic individuals, respectively. Groups were paired by age, sex, and body mass index (BMI). We evaluated the association between clinical and hormonal variables [thyrotropin, reverse T3 (rT3), total and free thyroxine (T4), and triiodothyronine (T3)] with the inflammation markers C-reactive protein (hs-CRP), serum amyloid A (SAA), and interleukin-6 (IL-6). Serum T3 and free T3 were lower in patients with diabetes (all P < 0.001) compared to the control groups. Interleukin-6 showed positive correlations with rT3 in both groups (P < 0.05). IL-6 was independently associated to FT3/rT3 (B = -0.193; 95% CI -0.31; -0.076; P = 0.002) and FT4/rT3 (B = -0.107; 95% CI -0.207; -0.006; P = 0.039) in the T1DM group. In the T2DM group, SAA (B = 0.18; 95% CI 0.089; 0.271; P < 0.001) and hs-CRP (B = -0.069; 95% CI -0.132; -0.007; P = 0.03) predicted FT3 levels. SAA (B = -0.16; 95% CI -0.26; -0.061; P = 0.002) and IL6 (B = 0.123; 95% CI 0.005; 0.241; P = 0.041) were related to FT4/FT3. In DM, differences in TH levels compared to non-diabetic individuals were related to increased subclinical inflammatory activity and BMI. Altered deiodinase activity was probably involved. These findings were independent of sex, age, BMI, and HbA1c levels.

Correlation between Serum Levels of 3,3',5'-Triiodothyronine and Thyroid Hormones Measured by Liquid Chromatography-Tandem Mass Spectrometry and Immunoassay

Objective

For measuring serum 3,3′,5′-triiodothyronine (rT3) levels, radioimmunoassay (RIA) has traditionally been used owing to the lack of other reliable methods; however, it has recently become difficult to perform. Meanwhile, liquid chromatography-tandem mass spectrometry (LC-MS/MS) has recently been attracting attention as a novel alternative method in clinical chemistry. To the best of our knowledge, there are no studies to date comparing results of the quantification of human serum rT3 between LC-MS/MS and RIA. We therefore examined the feasibility of LC-MS/MS as a novel alternative method for measuring serum rT3, thyroxine (T4), and 3,5,3′-triiodothyronine (T3) levels.

Methods

Assay validation was performed by LC-MS/MS using quality control samples of rT3, T4, and T3 at 4 various concentrations which were prepared from reference compounds. Serum samples of 50 outpatients in our department were quantified both by LC-MS/MS and conventional immunoassay for rT3, T4, and T3. Correlation coefficients between the 2 measurement methods were statistically analyzed respectively.

Results

Matrix effects were not observed with our method. Intra-day and inter-day precisions were less than 10.8% and 9.6% for each analyte at each quality control level, respectively. Intra-day and inter-day accuracies were between 96.2% and 110%, and between 98.3% and 108.6%, respectively. The lower limit of quantification was 0.05 ng/mL. Strong correlations were observed between the 2 measurement methods (correlation coefficient, T4: 0.976, p < 0.001; T3: 0.912, p < 0.001; rT3: 0.928, p < 0.001).

Conclusions

Our LC-MS/MS system requires no manual cleanup operation, and the process after application of a sample is fully automated; furthermore, it was found to be highly sensitive, and superior in both precision and accuracy. The correlation between the 2 methods over a wide range of concentrations was strong. LC-MS/MS is therefore expected to become a useful tool for clinical diagnosis and research.

Environmental heat stress modulates thyroid status and its response to repeated endotoxin challenge in steers

The objective of this study was to evaluate in cattle, the effects of acute exposure to a heat stress (HS) environment on the status of the pituitary (thyrotropin, TSH)-thyroid (thyroxine, T4)-peripheral tissue T4 deiodination (type 1 5'-deiodinase [D1]; triiodothyronine [T3]; reverse-triiodothyronine [rT3]) axis, and the further response of this pituitary-thyroid-peripheral tissue axis (PTTA) to perturbation caused by the induction of the proinflammatory innate immune state provoked by the administration of gram-negative bacteria endotoxin (lipopolysaccharide [LPS]). Ten steers (318 ± 49 kg body weight) housed in controlled environment chambers were subjected to either a thermoneutral (TN: constant 19°C) or HS temperature conditions (cyclical daily temperatures: 32.2°C-40.0°C) for a total period of 9 d. To minimize the effects of altered plane of nutrition due to HS, steers in TN were pair-fed to animals in HS conditions. Steers received 2 LPS challenges 3 d apart (LPS1 and LPS2; 0.2 μg/kg body weight, intravenously, Escherichia coli 055:B5) with the first challenge administered on day 4 relative to the start of the environmental conditioning. Jugular blood samples were collected at 0, 1, 2, 4, 7, and 24 h relative to the start of each LPS challenge. Plasma TSH, T4, T3, and rT3 were measured by radioimmunoassay. Liver D1 activity was measured in biopsy samples collected before the LPS1 (0 h) and 24 h after LPS2. Before the start of LPS1, HS decreased (P < 0.01 vs TN) plasma TSH (40%), T4 (45.4%), and T3 (25.9%), but did not affect rT3 concentrations. In TN steers, the LPS1 challenge decreased (P < 0.01 vs 0 h) plasma concentrations of TSH between 1 and 7 h and T4 and T3 at 7 and 24 h. In HS steers, plasma TSH concentrations were decreased at 2 h only (P < 0.05), whereas plasma T3 was decreased at 7 and 24 h (P < 0.01). Whereas plasma T4 concentrations were already depressed in HS steers at 0 h, LPS1 did not further affect the levels. Plasma rT3 concentrations were increased in all steers at 4, 7, and 24 h after LPS1 (P < 0.01). The patterns of concentration change of T4, T3, and rT3 during LPS2 mirrored those observed in LPS1; the responses in plasma TSH were of smaller magnitude than those incurred after LPS1. The LPS challenges reduced (P < 0.01) hepatic activity of D1 in all animals but no differences were observed between steers subjected to TN or HS environment. The data are consistent with the concept that acute exposure of cattle to a HS environment results in the depression of the pituitary and thyroid components of the PTTA, whereas a normal capacity to generate T3 from T4 in the liver is preserved. The data also suggest that LPS challenge further suppresses all components of the PTTA including liver T3 generation, and these PTTA perturbations are more pronounced in steers that encounter a HS exposure.

A novel mutation in the Albumin gene (R218S) causing familial dysalbuminemic hyperthyroxinemia in a family of Bangladeshi extraction

BACKGROUND

Familial dysalbuminemic hyperthyroxinemia (FDH) is a common cause of euthyroid hyperthyroxinemia. Clinical recognition of FDH is crucial for preventing unnecessary therapy in clinically euthyroid patients with abnormal thyroid function tests. Our goal was to identify the cause of abnormal serum tests of thyroid function in a Canadian family of Bangladeshi extraction.

PATIENTS

The proposita was found to have elevated free thyroxine (fT4) and free triiodothyronine (fT3) with nonsuppressed thyrotropin (TSH) on screening blood work. After detailed studies excluding hyperthyroidism and resistance to thyroid hormone, blood was obtained from all members of her immediate family for further investigation.

METHODS

We conducted laboratory analyses and sequencing of candidate genes.

RESULTS

Two members of this family have FDH, caused by a not previously identified mutation in the albumin gene. This mutation, located in exon 7 of the gene (652A>C), produces a single amino acid substitution in the protein molecule (R218S). The mutant albumin is associated with a ninefold increase in serum total T4 and a twofold increase in serum total reverse T3 compared to patients with normal albumin. Modeling data for the R218S variant are compatible with the increased binding affinity of this variant albumin for T4.

CONCLUSIONS

The R218S substitution reported here causes FDH that, in terms of the magnitude of serum iodothyronine elevation, is intermediate to the two previously reported mutations at codon 218 FDH: R218H being more mild and R218P more severe.

Inherited defects in thyroid hormone cell-membrane transport and metabolism

The description of two novel human defects in the last ten years has uncovered new aspects of thyroid hormone physiology with regard to cell-membrane transport and intracellular metabolism. Mutations in the X-linked monocarboxylate transporter 8 (MCT8) gene result in an invalidating neurodevelopmental phenotype in males and pathognomonic thyroid functions tests with high T3, low rT3, low or low normal T4, and normal or slightly high TSH. Recessive mutations in the selenocysteine insertion sequence binding protein 2 (SBP2) gene present a variable clinical phenotype depending on the severity of the defect and its consequences on the selenoprotein hierarchy. Most characteristic is the thyroid phenotype of low serum T3, high T4, high rT3, and slightly elevated TSH levels. Herein we review all known cases of MCT8 and SBP2 deficiency and describe each disease in terms of the clinical, biochemical, genetic, and therapeutic aspects.

Heredity and lifestyle in the determination of between-subject variation in thyroid hormone levels in euthyroid men

OBJECTIVE

Variation in thyroid hormone (TH) concentrations between subjects is greater than in a single subject over a prolonged period of time, suggesting an individual set point for thyroid function. We have previously shown that TH levels within normal range are associated with clinical indices such as bone mass, BMI, and heart rate. The aim of this study on young men was therefore to gain insight into the determinants of variation in TH levels among healthy subjects.

METHODS

Healthy male siblings (n=941, 25-45 years) were recruited in a cross-sectional, population-based study; a history or treatment of thyroid disease and thyroid auto-immunity were exclusion criteria. A complete assessment of TH status was performed (TSH, free thyroxine (FT4), free triiodothyronine (FT3), thyroperoxidase, and thyroglobulin antibodies, reverse T3 (rT3), thyroid-binding globulin (TBG), and urinary iodine levels). Genotyping was performed by TaqMan and KASP (KBiosciences) genotyping assays.

RESULTS

(F)T4, rT3, and TBG had heritability estimates between 80 and 90%. Estimates were lower for (F)T3 (60%) and lowest for TSH (49%). Significant associations were observed between different single-nucleotide polymorphisms (SNPs) in the thyroid pathway and TSH, FT4, ratio FT3:FT4, and rT3. Nevertheless, these SNPs only explain a limited part of the heredity. As to age and lifestyle-related factors, (F)T3 was negatively related to age and education level, positively to smoking and BMI (all P<0.0001) but not substantially to urinary iodine concentrations. Smoking was also negatively related to TSH and positively to FT4.

CONCLUSION

Both genetic and lifestyle-related factors play a role in determining between-subject variation in TH levels in euthyroid young men, although genetic factors seem most important.

Serum thyroid hormone levels in healthy children from birth to adulthood and in short children born small for gestational age

CONTEXT

Age-appropriate reference ranges for thyroid hormones are required for detecting pediatric thyroid dysfunction. Data on thyroid hormones and peripheral thyroid metabolism in short children born small for gestational age (SGA) before and during GH treatment are lacking.

OBJECTIVES

Our objectives were to obtain pediatric thyroid hormone reference ranges; to investigate thyroid hormones in short SGA children before puberty, during puberty, and during postponement of puberty by GnRH analog; and to evaluate thyroid hormones during GH treatment.

PATIENTS AND DESIGN

In 512 healthy children (225 females; 0-18 yr), free T(4) (FT(4)), TSH, total T(4), T(3), rT(3), and T(4)-binding globulin were determined. Reference ranges were calculated using the linearity, median, and skewness method. In 125 short SGA children (62 females; mean age 11.3 yr), thyroid hormones were analyzed before and after 2 yr of GH treatment and additional GnRH analog.

RESULTS

Thyroid references showed wide ranges postnatally and age-specific patterns thereafter, similar in boys and girls. Untreated short SGA children had similar FT(4) and T(4) levels as the reference population but significantly higher T(3), rT(3), and T(4)-binding globulin levels. During puberty and during GH treatment, FT(4) and rT(3) significantly decreased, whereas T(3) significantly increased.

CONCLUSION

Age-specific thyroid reference ranges are presented. Puberty and GH treatment both induce changes in peripheral thyroid metabolism, resulting in more biologically active T(3) at the expense of less inactive rT(3), possibly mediated by IGF-I. GH treatment induces altered peripheral thyroid metabolism but does not result in thyroid dysfunction.

Comparison and assessment of thyroid morphology and function in inhabitants of Lower Silesia before and after administration of a single dose of iodine-containing contrast agent during cardiac intervention procedure

INTRODUCTION

Inhabitants living in areas with endemic dietary iodine intake deficiency develop nodular goitre. The aim of our study was to evaluate thyroid morphology and function among adults residing in Lower Silesia and to assess the effect on the thyroid gland of an iodine-based contrasting agent administered during a cardiac intervention procedure.

MATERIALS AND METHODS

The first part of the study (evaluation of thyroid gland) was carried out on 120 subjects (78 men and 42 women). From among this group, invasive cardiac procedures were performed on 60 subjects (38 men and 22 women) during the second part of the study. Endocrine tests were repeated one, three, and six months after the invasive procedure.

RESULTS

1) Within the studied group, pathological changes in thyroid morphology were found in 49.1%, and thyroid function disturbances in 9.3%, of all subjects. 2) A decrease in TSH concentration with a corresponding increase in fT3 concentration was seen at the second visit (four weeks after iodine administration) leading to the diagnosis of hyperthyroidism in 15% of subjects.

CONCLUSIONS

1) Considering the multitude of silent thyroid pathologies, particular care is required before administering an iodine-based medium. 2) It is reasonable and advisable to monitor TSH and fT3 levels before and at four weeks after administration of an iodine-containing contrast agent. 3) Thyroid morphology and function disturbances after iodine administration do not necessitate treatment, as they are of transient character and only require monitoring.

Influence of thyroidectomy on thyroxine metabolism and turnover rate in rats

Little is known about the kinetics and metabolism of thyroid hormones in the hypothyroid state. To investigate these factors, we developed a reliable method for measurement of serum thyroxine (T(4)), triiodothyronine (T(3)), reverse-T(3) (rT(3)) and stable isotope-labeled T(4) ([(13)C(9)]T(4)), using online solid-phase extraction liquid chromatography-mass spectrometry/mass spectrometry (online SPE LC-MS/MS). We measured supply and turnover rates of T(4) in thyroidectomized (Tx) rats using [(13)C(9)]T(4) as a tracer. In rats, serum T(4), T(3) and rT(3) were decreased but not completely ablated after surgical Tx. Endogenous T(4) and T(3) levels in Tx rats were maintained at a constant low level throughout the experimental period. [(13)C(9)]T(4) levels declined with a half-life of ∼1.2 days after it was administered to Tx rats intravenously. These findings strongly suggest that serum T(4) levels in Tx rats are maintained by T(4) supplied by extra-thyroidal tissues (e.g. secretion of extra-thyroidal storage, enhancement of enterohepatic recirculation, and production in extra-thyroidal tissues). Moreover, the turnover rate of T(4) in Tx rats was approximately twofold lower than in controls. This finding suggests that degradation of serum T(4) is repressed by Tx. In conclusion, serum T(4) is maintained at a constant low level by T(4) supply from extra-thyroidal tissues and repression of T(4) degradation in Tx rats. The powerful online SPE LC-MS/MS tool can be used to investigate thyroid hormones kinetics and metabolism, and thus has the potential to be used as a diagnostic tool and to investigate the pathogenesis of thyroid disease.

T3/rT3-ratio is associated with insulin resistance independent of TSH

Thyroid dysfunction has been shown to be associated with insulin resistance (IR). This may involve peripheral thyroid hormone metabolism, which is assumed to be reflected by the ratio triiodothyronine/reverse triiodothyronine (T3/rT3-ratio). To explore a potential association between the T3/rT3-ratio and IR we investigated pairs which differed in IR, but were matched by sex, age, body mass index (BMI), and thyroid stimulating hormone (TSH). For this purpose, matched pair analyses were embedded into a cross sectional study group. 22 pairs were matched from either the first or the third tertile of HOMA%S of a cohort of 353 euthyroid subjects with normal glucose metabolism who did not take any medication. The T3/rT3-ratio was compared in the matched pairs. The T3/rT3-ratio was significantly increased in the insulin resistant subjects compared to their insulin sensitive partners (8.78 ± 0.47 vs. 7.33 ± 0.33, p=0.019). Furthermore the T3/rT3-ratio was lower in men compared to women (p for the within-subject effect=0.046) both in the insulin sensitive and the insulin resistant subjects. Here we show that the T3/rT3-ratio, which is supposed to reflect the tissue thyroid hormone metabolism, is significantly increased in insulin resistant subjects. This further supports a link between thyroid function and IR.

Transient changes in thyroid functions tests after zoledronic acid infusion

Zoledronic acid (ZA) induces an acute phase response in association with elevation of serum cytokines, which possibly alter the 3 types of iodothyronine deiodinase activity. We therefore studied the possible alteration in thyroid function tests by ZA. We investigated the acute changes in serum thyroid hormones, TSH, cortisol, white blood cells, CRP, interleukin-6 (IL-6) and tumor necrosis factor (TNF-α), before (0) and 1, 2 and 3 days after iv infusion of 5 mg ZA in 24 asymptomatic postmenopausal women with osteoporosis (ZA group) in comparison with a placebo group. In the majority of patients the ZA infusion was associated with acute phase response and fever within 24h after infusion which became attenuated on day three. Concurrently with increase in serum cortisol, CRP, IL-6 and TNF-α, on day 1 and 2, total serum T3 (TT3), free T3 (fT3), total T4 (TT4) and fT4 decreased with a nadir on day 2 in association with an increase in the fT4/fT3 ratio and reverse T3 (rT3) levels. All thyroid function changes returned to the baseline levels on day 3, with cytokines still at higher levels, although lower than those on day 2. Serum TSH remained essentially unchanged throughout the study. The changes in thyroid hormones were at least in part explained by the increased TNF-α, but not by IL-6. ZA induces short term changes in thyroid hormones, characteristic of nonthyroidal illness syndrome (NTIS), in association with an increase in TNF-α and IL-6.

Food restriction in young Japanese quails: effects on growth, metabolism, plasma thyroid hormones and mRNA species in the thyroid hormone signalling pathway

Young birds, in their post-natal growth period, may reduce their growth and metabolism when facing a food shortage. To examine how such responses can be mediated by endocrine-related factors, we exposed Japanese quail chicks to food restriction for either 2 days (age 6-8 days) or 5 days (age 6-11 days). We then measured growth and resting metabolic rate (RMR), and circulating 3,3',5-triiodo-l-thyronine (T3) and 3,5,3',5'-tetraiodothyronine (T4) levels as well as expression patterns of genes involved in growth (insulin-like growth factor-I: IGF-I) and thyroid hormone signalling (thyroid-stimulating hormone-beta: TSHbeta, type II iodothyronine deiodinase: D2, thyroid hormone receptors isoforms: TRalpha and TRbeta). The food-restricted chicks receiving a weight-maintenance diet showed reductions in structural growth and RMR. Plasma levels of both T3 and T4 were reduced in the food-restricted birds, and within the 5 days food-restricted group there was a positive correlation between RMR and T3. IGF-I mRNA showed significantly higher abundance in the liver of ad libitum fed birds at day 8 compared with food-restricted birds. In the brain, TSHbeta mRNA level tended to be lower in food-restricted quails on day 8 compared with controls. Furthermore, TRalpha expression was lower in the brain of food-restricted birds at day 8 compared with birds fed ad libitum. Interestingly, brain D2 mRNA was negatively correlated with plasma T3 levels, tending to increase with the length of food restriction. Overall, our results show that food restriction produced significant effects on circulating thyroid hormones and differentially affected mRNA species in the thyroid hormone signalling pathway. Thus, we conclude that the effects of food restriction observed on growth and metabolism were partly mediated by changes in the endocrine-related factors investigated.

Expression of thyroid hormone transporters during critical illness

OBJECTIVE

Prolonged critically ill patients have low circulating thyroid hormone (TH) levels without a rise in TSH, a condition labeled 'the low tri-iodothyronine (T(3)) syndrome'. Currently, it is not clear whether this represents an adaptive response. We examined the role of TH transporters monocarboxylate transporter 8 (MCT8, also known as SLC16A2) and MCT10 in the pathogenesis of the low T(3) syndrome in prolonged critical illness.

METHODS

A clinical observational study in critically ill patients and an intervention study in an in vivo animal model of critical illness. Gene expression levels of MCT8 and MCT10 were measured by real-time PCR.

RESULTS

In prolonged critically ill patients, we measured increased MCT8 but not MCT10 gene expression levels in liver and skeletal muscle as compared with patients undergoing acute surgical stress. In a rabbit model of prolonged critical illness, gene expression levels of MCT8 in liver and of MCT10 in skeletal muscle were increased as compared with healthy controls. Treatment of prolonged critically ill rabbits with TH (thyroxine+T(3)) resulted in a downregulation of gene expression levels of MCT8 in liver and of MCT10 in muscle. Transporter expression levels correlated inversely with circulating TH parameters.

CONCLUSIONS

These data suggest that alterations in the expression of TH transporters do not play a major role in the pathogenesis of the 'low T(3) syndrome' but rather reflect a compensatory effort in response to hypothyroidism.

Serum T4, T3, r-T3, TSH and Tg Levels in Cord Blood and Maternal Circulation at the Time of Delivery

The concentrations of T4, T3, r-T3, TSH and Tg were determined in parallel in maternal serum at the time of delivery and in cord blood. The serum T3 concentration in cord blood was significantly lower than that in the serum of the mother. However contrary to T3, r-T3 in cord serum was significantly higher than in maternal serum. Also, the level of TSH in cord blood was considerably higher than in maternal serum. The concentrations of total T4 in maternal and cord serum did not differ markedly, even though the values (mean and individual) were somewhat lower in the cord serum. The concentrations of Tg in cord and maternal serum varied widely, although the mean value for Tg in cord serum was somewhat higher than in maternal serum. No correlation was found between Tg concentration and TSH level in cord or maternal serum.

Time course of changes in free thyroid indices, rT3, TSH, cortisol and ACTH following exposure to sulfur mustard

In order to evaluate the time course of changes in serum concentration of thyroid hormones, cortisol and ACTH in patients exposed to chemical weapons containing sulfur mustard, we measured serum concentrations of hormones on the first, third and fifth week following injury in 13 soldiers and compared them to the results obtained from 34 control men. Free T4 and T3 indices were decreased and rT3, cortisol and ACTH were increased in the first week following exposure. There was a subnormal TSH response to TRH in 2 of 3 men tested. Except for an increase in FT4I and a decrease in TSH by the third week, and a steady decline in serum cortisol, serum hormone concentrations were unchanged until the fifth week after injury. The decline in serum cortisol occurred despite a constant increase in serum ACTH. By the fifth week only 1 of 13 men had serum cortisol levels > 10 micrograms/dl. We conclude that exposure to chemical weapons containing sulfur mustard results in alterations in serum concentrations of thyroid and adrenal hormones and ACTH, resembling changes seen in burn trauma. Some evidence of direct effects of mustard on endocrine glands exist.

Effects of selenium and iodine deficiency on type I, type II and type III iodothyronine deiodinases and circulating thyroid hormones in the rat

The effects of nutritional selenium (Se) deficiency over a period of three generations and of a combined selenium and iodine deficiency on hepatic and cerebrocortical iodothyronine deiodinases and on circulating thyroid hormone levels were examined in the rat. Se deficiency strongly decreased hepatic type I iodothyronine 5'- and 5-deiodinase to 6-13% of that in controls. Iodine depletion had only a marginal decreasing effect on the type I activity. Cerebrocortical type II 5'-deiodinase was decreased in Se-deficient, iodine-replete rats. Its 5-6-fold elevation in iodine-deficient rats was not reversed by additional selenium deficiency. Cortex type III 5-deiodinase was modestly decreased in all groups with insufficient trace element supply. Long-term Se deficiency has only limited effects on serum T4 and T3 levels. Two months of iodine deficiency decreased serum T4 to less than 10% of that in controls, but did not significantly affect serum T3 levels. The strong decrease of hepatic outer- and inner-ring deiodination of T4 in Se deficiency obviously reflects the reduced tissue concentration of the type I deiodinase which was recently identified as a selenoenzyme. The maintenance of increased cerebrocortical type II deiodinase in iodine-depleted animals irrespective of adequate or deficient selenium supply suggests that the type II isoenzyme does not contain selenium in its catalytic site. Further studies are necessary to clarify whether the weak, but repeatedly confirmed decrease of cortex type III deiodinase is the direct effect of Se deficiency or the indirect consequence of the multilevel change in thyroid hormone metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Radioimmunoassays of T3, r-T3 and r-T'2 in human serum

Simple radioimmunoassays for 3,3',5-triiodothyronine (T3), 3,3',5'-reverse-triiodothyronine (r-T3) and 3,3'-diiodothyronine (r-T'2) in human serum are described. The princple of the methods is the same and based on a system using 8-anilino-1-naphthalene sulfonic acid as an inhibitor of nonspecific protein binding, a simultaneous addition of the antibody and the labelled hormone, an overnight incubation at room temperature and a separation of bound and free hormone with dextran-coated charcoal. The methods require 15 microliter, 50 microliter and 100 microliter (or 333 microliter for ethanol extraction) serum respectively. Serum concentrations (mean +/- SD) of T3, r-T3 and r-T'2 from normal subjects are 144 +/- 19 ng T3/100 ml (n = 52), 32 +/- 7 ng r-T3/100 ml (n = 36), 3.8 +/- 0.7 ng r-T'2/100 ml (ethanol extraction, n = 18) and 8.2 +/- 1.6 ng r-T'2/100 ml (unextracted, n = 16).

Hypoglycemia and low S-T3--an experimental study

Ethanol-induced hypoglycemia after 44 hours of complete fasting was allowed to last for four hours. S-T3 decreased significantly (p less than 0.05), by 16.5%, S-rT3 remained unchanged and S-cortisol increased significantly (p less than 0.01). No correlation was found between S-T3 and S-cortisol. An association was found between S-T3 and blood glucose (p less than 0.05). An acute low S-T3 was achieved by depressing the peripheral availability and utilization of glucose. No association to a simultaneous increase in S-cortisol was found. An increase in S-rT3 failed to appear, probably also due to glucopenia.

The effect of suppressive therapy of nontoxic diffuse goiter on serum levels of thyroxine, 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine

We studied the effect of suppressive therapy with graded doses of thyroxine (T4) on serum levels of T4, 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine [rT3] in patients with diffuse, nontoxic goiter. For comparison and in order to elucidate the degree of suppression of the pituitary thyroid axis by T3 the effect of suppressive therapy with T3 was studied in the same type of patients. We found that T4 in serum rose significantly to a constant level during T4 treatment (0.10, 0.15 and 0.20 mg/day). Dose-related rises in T4 were only seen after 3 months of treatment. T3 and rT3 only changed minimally. The T4/T3 ratio rose to a constant level during the initial 3 months of treatment. T3/rT3 ratio remained unchanged. No dose-related differences in T4/T3 and T3/rT3 ratio were observed. Treatment with T3 in doses of 0.06 mg per day caused a significant but slow fall in T4 and rT3 to hypothroid levels while T3 only rose slightly. The T4/T3 ratio dropped significantly during T3 therapy.

Minor signs and symptoms of toxicity in a young woman in spite of massive thyroxine ingestion

The serum concentrations of thyroxine, 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine were followed during nine days in a case of acute thyroxine intoxication. On admission the concentrations were 11-12 times, 5-6 times and 16 times the normal mean, respectively. There was a striking discrepancy between the high concentrations of active hormones and the minor clinical symptoms.

The effect of acute and chronic exercise on thyroid hormones in obesity

Thyroid hormones were measured before, during and after acute exercise (60 min) or physical training (3 months) in obese women. Thyroid stimulating hormone concentration increased during acute work and decreased immediately after. No changes were seen during the two following days. An increase was seen after ten days as well as after three months of physical training. Thyroxine concentrations showed no changes. 3,5,3'-Triiodothyronine decreased slightly immediately after acute exercise, and after three months of physical training, 3,3',5'-triiodothyronine (reverse triiodothyronine) increased slowly during and after acute exercise. A negative correlation was found between changes in fasting insulin and thyroxine and a positive correlation between changes in blood pressure and triiodothyronine after training. Lack of agreement in previous reports is probably due to methodological differences such as methods more or less susceptible to fatty acid interference, and thyroid hormones changing differently during acute work and before and after physical training. The duration of the study may also be of importance, even 3 months possibly being too short for attaining equilibrium in thyroid homeostasis.

The effects of long-term antithyroid drug treatment on serum reverse T3 in patients with Graves' disease

The effects of long-term treatment with antithyroid drugs, carbimazole (CMI) or propylthiouracil (PTU), on serum reverse triiodothyronine (rT3) levels were studied in 23 patients with Graves' disease. Nineteen patients were given CMI and four PTU for a minimum of six months. After one month of treatment the serum levels of thyroxine (T4), triiodothyronine (T3) and rT3 had normalized in both groups. When L-thyroxine was added to the regimens after two months of therapy, both serum T4 and rT3 levels increased, whereas serum T3 level continued to fall. The serum levels of rT3 seemed to be dependent on and followed the T4 levels so closely that determinations of rT3 in the medical management of patients with Graves' disease will be of little clinical use.

T4, T3 and reverse-T3 determinations in connection with the TRH test in the evaluation of possible hyperthyroidism

One disadvantage of the TRH test is that an absent or blunted TSH response is seen not only in hyperthyroid patients but also in some normal subjects. The aim of the present study was to elucidate whether the discriminatory power between eu- and hyperthyroidism could be increased by determining the T3 and T4 levels before and after the TRH administration. The study population consists of 30 patients referred for evaluation of suspected hyperthyroidism. The results show that all but one of the patients (n=20) who had T3 levels within the normal reference limits increased these levels after TRH administration, whether their TSH response was normal or blunted. One patient's T3 levels decreased after TRH. All the patients (n=10) who had T3 levels within the hyperthyroid range showed a decrease after TRH. The decrease was significantly correlated (r=0.90) to the magnitude of the increase. No consistent T4 and no change in reverse-T3 response was obtained. The addition of T3, T4 or reverse-T3 determinations in connection with the TRH test does not seem to increase the discriminatory power of the test.

Non-selective and selective beta-1-adrenoceptor blocking agents in the treatment of hyperthyroidism

Treatment for one month with propranolol or atenolol, a selective beta-1-adrenoceptor blocking agent, was evaluated in 20 hyperthyroid patients. The patients improved to the same extent on either drug, as shown by a clinical diagnostic index. Basal metabolic rate decreased by 11% during both treatments, while it was unchanged in seven untreated hyperthyroid controls. Thyroxine concentration did not change during any treatment. During propranolol treatment T3 decreased from 4.6 to 3.9 nmol/l, while no changes were observed during atenolol treatment or in the control group. No significant changes were seen in free T4, free T3 or rT3 concentrations on any treatment, although free T3 was observed to decrease slightly during propranolol treatment. Thus, the improvement of the clinical symptoms of hyperthyroidism cannot be explained by diminished thyroid hormone concentrations in serum, since the reduction was small during propranolol and absent during atenolol treatment.

The influence of endogenous cortisol on the peripheral conversion of thyroxine in patients with acute myocardial infarction

A study was performed to elucidate whether endogenous cortisol, as previously suggested, could be responsible for the decreased T3 levels seen in euthyroid patients with acute myocardial infarction. Levels of these hormones as well as levels of T4 and reverse-T3 were monitored in 31 consecutive patients admitted to the Coronary Care Unit with symptoms of precordial pain or with acute arrhythmias. Sixteen of the patients had proven myocardial infarction, the remaining 15 were used as a control group. The results demonstrated that a reduction of T3 levels was seen in the infarction group without evidence of a statistically significant difference between the daily mean cortisol levels. No significant difference could be observed in T4 or reverse-T3 levels in the two groups or in T3 levels in the control group. It is concluded that the decrease in T3 levels is not a consequence of the increased levels of endogenous cortisol.

The influence of propranolol on the extrathyroidal metabolism of 3,3',5'-triiodothyronine (reverse T3)

The effect of propranolol 80 mg daily on the metabolism of 3,3',5'-triiodothyronine (reverse T3, rT3), 3,3',5'-triiodothyronine (T3) and thyroxine (T4) was studied by means of a non compartmental kinetic method in seven females with severe pretreatment hypothyroidism. The patients were maintained euthyroid on a constant L-T4 replacement therapy. Serum rT3 levels increased significantly during propranolol (p less than 0.02). This increase was explained by a decrease in metabolic clearance rate (MCR) (p less than 0.02), since the conversion rate from T4 and the distribution volume of rT3 were unchanged. By contrast the decreased serum levels of T3 were due to a significant decreased conversion from T4 (p less than 0.02) in spite of a decreased MCR. The results are compatible with the assumption of two different monodeiodinating enzymes, a 5-deiodinase responsible for the diodination of T4 to rT3 and a 5'-deiodinase responsible for the deiodination of T4 to T3.

Very early changes in circulating T3 and rT3 during development of metabolic derangement in diabetic patients

Alterations in circulating iodothyronines were studied in 15 juvenile type diabetic patients during the development of metabolic derangement after withdrawal of insulin. By means of measurements of circulating C peptide, one group of patients with and one without residual beta-cell function had been selected. In both groups there was a gradual decrease in serum T3 during the 12-hour period studied after withdrawal of insulin, while an increase in serum rT3 was observed after 4-6 hours. The alterations in serum T3 and the metabolic derangement were significantly more pronounced in patients without than with residual beta-cell function.

Increased reverse triiodothyronine is associated with shorter survival in independently-living elderly: the Alsanut study

OBJECTIVE

Increased reverse tritiodothyronine (T(3)) used to be described as a part of euthyroid sick syndrome (ESS). It was demonstrated to be associated with increased mortality in acutely ill patients. It can also be found with low or normal T(3) in non-severely ill subjects but its significance remains unclear.

PATIENTS AND DESIGN

The Alsanut study included a representative sample of 440 independently-living subjects aged 65 or over constituted between January 1988 and September 1989. Past and current medical history and nutritional data were collected at inclusion. Baseline thyroid hormone (TSH, FT(4), FT(3) and rT(3)) serum levels were measured. Life status was determined on 1 December 2005.

RESULTS

Of the 374 elderly subjects included in the final analysis, 52 had abnormal TSH (43 with hyperthyroidism, nine with hypothyroidism) and 80.7% had died by 1 December 2005. There was no statistical difference in survival between subjects according to thyroid function (P=0.54). Of the 322 elderly subjects with normal TSH, mortality rate was 81.1%. ESS was found in 3.4%, whereas 8.1% of the participants displayed elevated rT(3) with normal FT(3). Time to death was strongly related to rT(3) (P<0.0001) and FT(3) (P<0.0001) in a univariate analysis. After adjusting for other confounding variables, rT(3) was the only thyroid hormone associated with shorter survival (P=0.014).

CONCLUSIONS

RT(3) was the only thyroid hormone associated with shorter survival in a representative population of independently-living elderly. In these subjects, isolated elevated rT(3) might be an equivalent of ESS, reflecting declining health.

Effects of substitution and high-dose thyroid hormone therapy on deiodination, sulfoconjugation, and tissue thyroid hormone levels in prolonged critically ill rabbits

To delineate the metabolic fate of thyroid hormone in prolonged critically ill rabbits, we investigated the impact of two dose regimes of thyroid hormone on plasma 3,3'-diiodothyronine (T(2)) and T(4)S, deiodinase type 1 (D1) and D3 activity, and tissue iodothyronine levels in liver and kidney, as compared with saline and TRH. D2-expressing tissues were ignored. The regimens comprised either substitution dose or a 3- to 5- fold higher dose of T(4) and T(3), either alone or combined, targeted to achieve plasma thyroid hormone levels obtained by TRH. Compared with healthy animals, saline-treated ill rabbits revealed lower plasma T(3) (P=0.006), hepatic T(3) (P=0.02), and hepatic D1 activity (P=0.01). Substitution-dosed thyroid hormone therapy did not affect these changes except a further decline in plasma (P=0.0006) and tissue T(4) (P=0.04). High-dosed thyroid hormone therapy elevated plasma and tissue iodothyronine levels and hepatic D1 activity, as did TRH. Changes in iodothyronine tissue levels mimicked changes in plasma. Tissue T(3) and tissue T(3)/reverse T(3) ratio correlated with deiodinase activities. Neither substitution- nor high-dose treatment altered plasma T(2). Plasma T(4)S was increased only by T(4) in high dose. We conclude that in prolonged critically ill rabbits, low plasma T(3) levels were associated with low liver and kidney T(3) levels. Restoration of plasma and liver and kidney tissue iodothyronine levels was not achieved by thyroid hormone in substitution dose but instead required severalfold this dose. This indicates thyroid hormone hypermetabolism, which in this model of critical illness is not entirely explained by deiodination or by sulfoconjugation.

Exploring the use of recombinant human TSH in the diagnosis of central hypothyroidism

CONTEXT

The diagnosis of central hypothyroidism (CH) is often difficult to establish as serum TSH levels may be low, normal, or slightly increased.

OBJECTIVE

To explore the use of recombinant human TSH (rhTSH) in the diagnosis of CH.

DESIGN

Randomized single-blind clinical trial.

SETTING

Outpatient clinic of a tertiary care referral center.

INTERVENTION

A single intramuscular injection of 0.1 and 0.9 mg rhTSH in random order with 1-week interval.

PARTICIPANTS

Eighteen adult patients with pituitary insufficiency and six healthy age-, sex-, and body mass index-matched controls. Six patients had untreated CH (newCH), six had treated CH (CH), and six patients were TSH sufficient (nonCH). Five weeks before TSH stimulation, levothyroxine was replaced with tri-iodothyronine (T(3)) for 4 weeks. One week before stimulation, treatment was withdrawn.

MAIN OUTCOME MEASURES

Thyroid hormones and thyroglobulin (Tg) before and 2, 3(1/2), 7, 24, 48, and 72 h after each injection.

RESULTS

In the newCH group, basal free thyroxine (FT(4)) levels were lower than in controls (P<0.05). After 0.9 mg rhTSH, the increases in FT(4) and reverse T(3) (rT(3)) were less marked in the newCH group than in controls (FT(4)+/-s.e.m. 9.2+/-0.5 to 19.7+/-1.2 vs 11.3+/-0.5 to 27.8.2+/-2.4 pmol/l, P<0.05). The CH group exhibited reduced basal and stimulated FT(4) compared with the TSH-sufficient groups. Tg increased similarly among all study groups after rhTSH injection.

CONCLUSION

In this pilot study, patients with untreated CH had lower response to 0.9 mg rhTSH in FT(4) and rT(3) than controls. An rhTSH test may be useful in the diagnosis of CH, but further studies are required.

Non thyroidal illness: to treat or not to treat?

In critically ill patients, pronounced alterations in the hypothalamic-pituitary-thyroid axis occur without any evidence for thyroid disease. T3 decreases and rT3 increases within a few hours of the onset of disease. Severity and duration of disease are related to the magnitude of these changes. This manuscript discusses whether these changes in thyroid hormone levels during critical illness should be treated, and was in part published elsewhere.

The Asp727Glu polymorphism in the TSH receptor is associated with insulin resistance in healthy elderly men

BACKGROUND

Variations in thyroid function within the normal range are associated with differences in metabolism and body composition. For instance, TSH is positively associated with body mass index (BMI). This could be due to alterations in thyroid hormone activity, or to direct effects of TSH, as the TSH receptor (TSHR) is also expressed in adipose tissue. The TSHR-Asp727Glu polymorphism is associated with lower serum TSH levels in vivo. In this study, we analysed whether serum thyroid parameters and the TSHR-Asp727Glu polymorphism were associated with glucose metabolism and insulin resistance. In addition, we analysed the Thr92Ala polymorphism in the type 2 deiodinase (D2), which was recently associated with insulin resistance.

METHODS

Genotypes were determined in a population of 349 elderly men (age 77.7 +/- 3.5 years), for whom serum thyroid parameters and data on insulin resistance, such as fasting blood glucose, serum insulin and homeostasis model assessment (HOMA) values, were available.

RESULTS

In nondiabetic, euthyroid subjects, TSH was positively associated with leptin levels, whereas FT4 and rT3 were significantly negatively correlated with insulin and HOMA. Carriers of the TSHR-Glu727 allele had a significantly higher glucose (P = 0.01), insulin (P = 0.001), glycated haemoglobin (HbA1c) (P = 0.002), HOMA (P = 0.001) and leptin (P = 0.008). The D2-Ala(92) allele showed a trend towards higher levels of insulin (P = 0.07) and a higher HOMA (P = 0.09).

CONCLUSION

In this population of nondiabetic elderly men, serum thyroid parameters and the TSHR-Asp727Glu polymorphism were associated with relative insulin resistance. Our study suggests that genetic variation in TSHR plays a role in insulin resistance and thereby influences glucose metabolism.

Differential T4 degradation pathways in young patients with preterminal and terminal renal failure

INTRODUCTION

The aim of this study is to analyze thyroid hormone parameters in large homogenous patient cohorts with preterminal (stage 4) and terminal (stage 5) renal failure in an area of low iodine intake.

PATIENTS AND METHODS

Thyroid parameters were measured in healthy controls (n=48), patients with preterminal renal failure (n=48) and patients with terminal renal failure undergoing hemodialysis (n=288). All patients were assessed by measurement of TSH, T4, T3, fT4, rT3, Tg and TPO-antibodies.

RESULTS

There was a significant decrease of T4 and fT4 from healthy controls to patients with preterminal renal failure and to patients with terminal renal failure. T3 showed a decrease from healthy controls to patients with preterminal renal failure and to patients with terminal renal failure (1.54+/-0.06 microg/l VS. 1.05+/-0.05 microg/l VS. 1.09+/-0.23 microg/l, p<0.001 VS. controls). rT3 was significantly decreased in patients with terminal renal failure (0.24+/-0.01 microg/l VS. 0.25+/-0.02 microg/l VS. 0.16+/-0.01 microg/l, p<0.001). The rT3/T3 ratio was significantly elevated in patients with preterminal renal failure (p<0.01). TSH concentrations were in the normal range in all groups.

CONCLUSION

Our data suggest different T4 degradation pathways in patients with preterminal and terminal renal failure.

Effects of evening vs morning thyroxine ingestion on serum thyroid hormone profiles in hypothyroid patients

OBJECTIVE

Standard drug information resources recommend that l-thyroxine be taken half an hour before breakfast on an empty stomach, to prevent interference of its intestinal uptake by food or medication. We observed cases in which TSH levels improved markedly after changing the administration time of l-thyroxine to the late evening. We therefore conducted a pilot-study to investigate whether l-thyroxine administration at bedtime improves TSH and thyroid hormones, and whether the circadian rhythm of TSH remains intact. DESIGN Patients were studied on two occasions: on a stable regimen of morning thyroxine administration and two months after switching to night-time thyroxine using the same dose. On each occasion patients were admitted for 24 h and serial blood samples were obtained.

PATIENTS

We investigated 12 women treated with l-thyroxine because of primary hypothyroidism, who used no medication known to interfere with l-thyroxine uptake.

MEASUREMENTS

Patients were admitted to hospital and blood samples were obtained at hourly intervals for 24 h via an indwelling catheter. Following this first hospital admission, all women were asked to switch the administration time from morning to bedtime or vice versa. After 2 months they were readmitted for a 24-h period of hourly blood sampling. Blood samples were analysed for serum TSH (immunometric assay), FT4 and T3 (competitive immunoassay), T4 and rT3 (radioimmunoassay), serum TBG (immunometric assay) and total protein and albumin (colourimetric methods).

RESULTS

A significant difference in TSH and thyroid hormones was found after switching to bedtime administration of l-thyroxine. Twenty-four-hour average serum values amounted to (mean +/- SD, morning vs bedtime ingestion): TSH, 5.1 +/- 0.9 vs 1.2 +/- 0.3 mU/l (P < 0.01); FT4, 16.7 +/- 1.0 vs 19.3 +/- 0.7 pmol/l (P < 0.01); T3, 1.5 +/- 0.05 vs 1.6 +/- 0.1 nmol/l (P < 0.01). There was no significant change in T4, rT3, albumin and TBG serum levels, nor in the T3/rT3 ratio. The relative amplitude and time of the nocturnal TSH surge remained intact.

CONCLUSIONS

l-thyroxine taken at bedtime by patients with primary hypothyroidism is associated with higher thyroid hormone concentrations and lower TSH concentrations compared to the same l-thyroxine dose taken in the morning. At the same time, the circadian TSH rhythm stays intact. Our findings are best explained by a better gastrointestinal uptake of l-thyroxine during the night.

Genetic variation in thyroid hormone pathway genes; polymorphisms in the TSH receptor and the iodothyronine deiodinases

Serum thyroid parameters show substantial inter-individual variability, in which genetic variation is a major factor. Findings in patients with subclinical hyper- and hypothyroidism illustrate that even minor alterations in serum thyroid function tests can have important consequences for a variety of thyroid hormone-related clinical endpoints, such as atherosclerosis, bone mineral density, obesity, and heart rate. In the last few years, several studies described polymorphisms in thyroid hormone pathway genes that alter serum thyroid function tests. In this review, we discuss the genetic variation in the TSH receptor and iodothyronine deiodinases. We discuss the possible consequences of these studies for the individual patient and also the new insights in thyroid hormone action that can be obtained from these data.

Down Syndrome and Thyroid Gland

Down Syndrome (DS) or trisomy 21 (T21) is the most frequent and the best known malformation syndrome associated with mental deficiency that appears in human,. Average incidence of this syndrome is about 1:700 newborns. Numerous researchers noted thyroid disorders in people with Down Syndrome but, clinical symptoms of thyroid dysfunction are difficult to separate from DS phenotype. The aim of this study was to examine the thyroid function in the patients with DS. Our results confirmed higher frequency of thyroid dysfunction in DS patients. Higher values of TSH were found in 60,34% of the examined DS patients, which is significantly higher value comparing with the control group (p<0,01). Compensated hypothyroidism was established in 27,92% of the examined DS patients, and most of those (63,23%) were younger than 6 years. The conclusions emphasize the necessity of implementation of thyroid function screening program in persons with DS, and the need for adequate treatment of its dysfunction. Thus, the symptoms of the disease would be alleviated and better physical and mental fitness ensured.

Effect of long-term calorie restriction with adequate protein and micronutrients on thyroid hormones

CONTEXT

Caloric restriction (CR) retards aging in mammals. It has been hypothesized that a reduction in T(3) hormone may increase life span by conserving energy and reducing free-radical production.

OBJECTIVE

The objective of the study was to assess the relationship between long-term CR with adequate protein and micronutrient intake on thyroid function in healthy lean weight-stable adult men and women.

DESIGN, SETTING, AND PARTICIPANTS

In this study, serum thyroid hormones were evaluated in 28 men and women (mean age, 52 +/- 12 yr) consuming a CR diet for 3-15 yr (6 +/- 3 yr), 28 age- and sex-matched sedentary (WD), and 28 body fat-matched exercising (EX) subjects who were eating Western diets.

MAIN OUTCOME MEASURES

Serum total and free T(4), total and free T(3), reverse T(3), and TSH concentrations were the main outcome measures.

RESULTS

Energy intake was lower in the CR group (1779 +/- 355 kcal/d) than the WD (2433 +/- 502 kcal/d) and EX (2811 +/- 711 kcal/d) groups (P < 0.001). Serum T(3) concentration was lower in the CR group than the WD and EX groups (73.6 +/- 22 vs. 91.0 +/- 13 vs. 94.3 +/- 17 ng/dl, respectively) (P < or = 0.001), whereas serum total and free T(4), reverse T(3), and TSH concentrations were similar among groups.

CONCLUSIONS

Long-term CR with adequate protein and micronutrient intake in lean and weight-stable healthy humans is associated with a sustained reduction in serum T(3) concentration, similar to that found in CR rodents and monkeys. This effect is likely due to CR itself, rather than to a decrease in body fat mass, and could be involved in slowing the rate of aging.

Thyroid hormones, dementia, and atrophy of the medial temporal lobe

CONTEXT

Thyroid function has been related to Alzheimer disease (AD), but it remains unclear whether thyroid dysfunction results from or contributes to developing AD.

OBJECTIVE

The objective of the study was to determine the association between thyroid function and both medial temporal lobe atrophy on brain magnetic resonance imaging (MRI) as putative early sign of AD and risk of dementia.

DESIGN AND PARTICIPANTS

This was a population-based cohort study among 1077 elderly subjects aged 60-90 yr and dementia free at baseline (1995-1996).

MAIN OUTCOME MEASURES

Nonfasting serum levels of TSH, free T(4) (fT(4)), T(3), and rT(3) were available in 1025 subjects followed up for incident dementia until 2005. In a subset of 489 nondemented elderly, we assessed volumes of the hippocampus and amygdala on brain MRI. Subjects using thyroid medication were excluded.

RESULTS

During 5657 person-years of follow-up (mean 5.5 yr), 63 subjects were diagnosed with dementia (46 with AD). TSH and thyroid hormones were not associated with risk of dementia or AD. TSH and T(3) were also not related to brain atrophy, whereas nondemented subjects with higher fT(4) levels had more hippocampal and amygdalar atrophy on MRI. Similar associations were found for rT(3). Excluding subjects with thyroid disorders or incipient AD did not change the results.

CONCLUSION

In our study, TSH was related neither to risk of AD nor with early MRI markers thereof, arguing against an important role of thyroid function in the development of AD. Whether the association of higher fT(4) and rT(3) levels with brain atrophy on MRI has functional significance remains to be elucidated.

Subclinical Hypothyroidism in HIV-Infected Patients Is Not an Autoimmune Disease

AIMS AND METHODS

A study of 350 HIV+ patients in our region showed that 16% suffered from hypothyroidism. Twenty-two HIV+ hypothyroid patients (10 with subclinical hypothyroidism, 12 with low FT4 levels (LT4) (confirmed by a dialysis equilibrium assay) and 22 HIV+ euthyroid controls receiving highly active anti-retroviral therapy were included in an additional study.

RESULTS

No goiter or anti-thyroid antibodies were detected. Use of stavudine was more frequent in the LT4 subgroup (p < 0.01) and subclinical hypothyroidism group (p = 0.04). Use of didanosine (OR, 12.5, p < 0.01) and ritonavir (OR, 33.0, p < 0.01) was more frequent in the LT4 subgroup, with a greater didanosine cumulative dose (616.7 mg [180.0, 1,260.0] vs. 263.7 [63.0, 948.0], p = 0.01). Reverse T3, binding protein levels, the TSH response to thyrotropin-releasing hormone, urinary iodine, plasma selenium and thiocyanate levels did not differ. IFNgamma levels were lower in the subclinical hypothyroidism group (pg/ml) (9.1 [0.0, 22.7] vs. 19.5 [0.0, 40.9], p = 0.03).

CONCLUSION

None of the investigated mechanisms are able to explain the occurrence of hypothyroidism in HIV patients receiving highly active anti-retroviral therapy except the anti-retroviral treatment. In light of the absence of autoimmunity, the normal adenohypophysis and thyroid responses to thyrotropin-releasing hormone, central hypothyroidism is suspected and could explain LT4 and high TSH levels. Underlying mechanisms need further exploration.

Grenzen und Bedeutung der Labordiagnostik bei Mangelernährung im Alter

Despite the widespread interest in malnutrition in the elderly, the utility of laboratory tests is limited. This is because their diagnostic significance can be impaired by undercurrent diseases, pre-analytical effects and unsatisfactory standardization. This survey summarizes the most important parameters of malnutrition. Thus, "nitrogen balance" is considered the golden standard of nutrition status, while the diagnostic significance of serum proteins depends on their biological half-time. Albumin is seen as the most reliable malnutrition marker, but cholinesterase and cholesterol-decrease must also be mentioned. The so-called "low-T3-phenomenon" which is caused by the production of "reverse T3", seems to be the unique parameter for the "catabolic" state of metabolism. Of special interest are also prognostic markers of mortality, such as orosomucoid. Cytokines, other signal peptides, trace elements and vitamins are from the diagnostic point of view of rather limited significance. In sum, the diagnosis and monitoring of malnutrition in the elderly represents an important challenge for laboratory medicine.

The relationship between iron status and thyroid hormone concentration in iron-deficient adolescent Iranian girls

Extensive data from animal and human studies indicate that iron deficiency impairs thyroid metabolism. The aim of this study was to determine thyroid hormone status in iron-deficient adolescent girls. By stepwise random sampling from among all public high schools for girls in Lar and its vicinity in southern Iran, 103 out of 431 iron deficient subjects were selected. Urine and serum samples were collected and assayed for urinary iodine and serum ferritin, iron, total iron binding capacity (TIBC), thyroid stimulating hormone (TSH), thyroxine (T4), triiodothyronine (T3), free thyroid hormones (fT4 and fT3), triiodothyronine resin uptake (T3RU), reverse triiodothyronine (rT3), selenium and albumin concentrations. Hematological indices for iron status confirmed that all subjects were iron-deficient. There was a significant correlation between T4 and ferritin (r = 0.52, P < 0.001) and between TSH and ferritin (r = -0.3, P < 0.05). Subjects with low serum ferritin had a higher ratio of T3/T4 (r = -0.42, P < 0.01). Using stepwise regression analysis, only ferritin contributed significantly to the rT3 concentration (r = -0.35, P < 0.01). The results indicate that the degree of iron deficiency may affect thyroid hormone status in iron-deficient adolescent girls.

Hormone levels in children during the first week of ICU-admission: is there an effect of adequate feeding?

BACKGROUND & AIMS

To evaluate the course of hormonal parameters in relation to clinical parameters, illness severity and nutritional intake in children admitted to the pediatric ICU during the first week of admission.

METHODS

Prospective, observational study. Levels of triiodothyronine (T3), reverse T3 (rT3), ratio T3/rT3 and insulin-like growth factor I (IGF-1) were evaluated in 84 critically ill children (50 term neonates and 34 children aged 32 d-15 yr) admitted to our multidisciplinary tertiary pediatric intensive care unit within 24 h after admission, on days 4 and 6 after admission. Changes in hormones levels over time were related to illness severity, C-reactive protein-levels and the adequacy of feeding.

RESULTS

For both age groups IGF-1 levels remained low until day 4, but at day 6 IGF-1 levels were significantly higher than admission level. In 88% and 89% of the older children, T3 levels remained below normal at days 4 and 6, respectively. In both age groups, rT3 levels declined significantly over time, whereas the ratio T3/rT3 increased. The increases in IGF-1, T3 and ratio T3/rT3 and decrease in rT3 were significantly associated with decreases in CRP-levels. No significant relations were found between changes in IGF-1 and thyroid hormone levels during admission and the adequacy of energy and protein intake.

CONCLUSIONS

During the first week of ICU-admission, abnormalities in levels of IGF-1, T3 and rT3 were frequently observed in critically ill children, especially in the children aged >1 month. The adequacy of feeding did not seem to affect the normalization of IGF-1 and thyroid hormone levels.

Transient Hypothyroxinemia in Severe Hypertensive Disorders of Pregnancy

OBJECTIVE

Assess whether and to what extent thyroid function is affected in pregnant women with early and severe hypertensive disorders and in their newborns.

METHODS

Patients were 80 women with preeclampsia, hemolysis, elevated liver enzymes, and low platelet count syndrome or gestational hypertension combined with fetal growth restriction in the 24th to 34th week of singleton pregnancies. Maternal thyroid hormone levels and thyroid peroxidase antibodies were determined at admission and 3 months postpartum. Neonatal levels were determined from cord blood at delivery. Maternal hypothyroxinemia was defined as free T(4) (fT(4)) value below 9 pM.

RESULTS

At admission 26 (33%) women in the study group had fT(4) levels below 9 pM, with spontaneous normalization during pregnancy. There were no statistically significant differences between thyroid hormone values in women in the study group and 10 normotensive pregnant women in their third trimester. Three months postpartum, 97.5% of patients had normal thyroid hormone levels. Thyroid peroxidase antibodies were elevated in 10% of women postpartum. Their infants, born at a median gestational age of 30 6/7 weeks, had lower cord blood fT(4) and thyroid-stimulating hormone values compared with preterm infants of the comparison group, appropriate for gestational age. Cord blood fT(4) had no correlation with gestational age or maternal fT(4), but there was a significant correlation of cord blood fT(4) with umbilical artery pH.

CONCLUSION

Women with severe hypertensive disorders of pregnancy may have transiently lower fT(4) levels, without evidence of a thyroid disorder. Their neonates have lower fT(4) levels at birth unrelated to maternal fT(4), but related to prenatal acidosis.

LEVEL OF EVIDENCE

II-2.