Basal Thyroid Hormone Levels Research Articles

Adequacy of equine thyroid function testing in mares

The gold standard for thyroid function in horses is a thyroid releasing hormone (TRH) response test. We hypothesized that published reference values for thyroxine (T4), triiodothyronine (T3) would apply to mares in an iodine deficient zone. Our objective was to evaluate basal thyroid hormone levels and TRH responses in twenty-seven healthy Quarter Horse type mares fed grass hay, oats, with free access to cobalt iodine salt blocks and mean ± SD age of 9.2 ± 4.4 years, and weight of 527 ± 65.1 kg. Four mares were 10 to 35 days pregnant. Physical examinations were within normal limits including palpation and ultrasound of the thyroid gland. TRH response tests were performed mornings from July to September. A basal jugular blood sample (0 h) was obtained, TRH (1 mg IV, Sigma) was administered, and additional samples obtained at 2 h for T3 and 4 h for T4. Definitions: Fold change (FC) post-TRH level / basal level; Euthyroid basal T4 (12.87-38.6 nmol/L) and T3 (0.41-1.1 nmol/L) within reference ranges of Animal Health Diagnostic Lab, Ithaca, NY and TRH T4 and T3 responses with a FC >2. The Post TRH FC reference ranges for T4 and T3 reported by Breuhaus (2018) were also evaluated (T4 FC 1.3-3.8; T3 FC 1.1-10). Serum was separated and stored at -20C. A single assay was performed to measure T3 and T4 using the Siemen's Immulite method (PDS, Saskatoon, SK). Data were evaluated using Shapiro Wilk, Kruskal Wallis and Spearman Rank Correlation at P < .05. Low basal levels were measured in three mares for T3 (11%), and two for T4 (7.4%). Ten mares had T3 levels with a FC<2 (37%), and two had FC<1.1 (7.4%). Regarding T4 twenty-two mares (81%) had a FC<2 and ten had a FC <1.3 (37%). The FC was below the reference range for both T3 and T4 in two mares. There were significant correlations between basal T3 and T4 (R=0.47 P=.012) and between T3 FC and T4 FC (R=0.64, P=.0001), and no effect of pregnancy. We concluded that basal T3 and T4 values were too variable to assess thyroid function, as mares with low basal values usually had a FC>2. Using FC >2 as an adequate TRH response is problematic as a FC<2 was identified in 37% of T3 and 81% of T4 mares. There were 7.4% and 37% of mares below the low end of the FC reference for T3 and T4 respectively. These low values may indicate that the mares were hypothyroid, which is often due to underlying iodine insufficiency. Iodine status and its relationship to the thyroid response to TRH should be further evaluated due to iodine's central role in equine health.

Analysis of basal serum TSH, FT3, and FT4 levels based on age, sampling time in women with infertility

BackgroundTo analyze the characteristics of basal thyroid hormone levels in infertile women consulting for assisted reproductive technology (ART) treatment.MethodsThis was a retrospective study. Serum TSH, FT3 and FT4 levels of women seeking ART consultation were tested routinely. Analyses were performed based on age and sampling time. One-way ANOVA or Kruskal-Wallis rank sum test was used to compare the continuous data among the groups, and the chi-square test or Fisher’s exact test was used to compare categorical data where appropriate.ResultsA total of 6426 women were initially included in the study. After exclusion criteria were applied, the remaining 4126 women were categorized into different groups. The prevalence of subclinical hypothyroidism significantly decreased with age and sampling time, from 21.09 to 11.91% and from 28.57 to 10.67%, respectively (P < 0.001, respectively). Mean serum TSH, FT3, and FT4 levels decreased significantly with age (P = 0.017, < 0.001, < 0.001, respectively). In the context of sampling time, TSH levels from early in the morning were significantly higher (P < 0.001), while FT4 and FT3 levels were similar in different groups (P = 0.258, 0.300, respectively).ConclusionsThe prevalence of subclinical hypothyroidism significantly decreased with increasing age and sampling time, as did the serum TSH levels. Even though, the establishment of reference interval of TSH level based on age or sampling time was not recommended. Full consideration of age and sampling time should be carefully taken before initiation of treatment.

Effects of modified Atkins diet on thyroid function in adult patients with pharmacoresistant epilepsy

IntroductionThe use of ketogenic diet as a supplement to antiseizure medication (ASM) in refractory epilepsy has increased the past decades. This high-fat, low-carbohydrate diet mimics the metabolic state of fasting and is generally well-tolerated. However, the long-term adverse effects of the diet are unclear.The purpose of this study was to investigate whether the modified Atkins diet (MAD), a variant of the ketogenic diet, may have an impact on thyroid hormone levels. MethodsWe assessed thyroid function by measuring thyroid stimulation hormone (TSH), fT4, T3, fT3, and rT3 before diet start (baseline) and after 12 weeks on the diet in 53 adult patients with drug-resistant epilepsy. Further, we examined the correlation between the changes in thyroid function during dietary treatment and type of (i) change in seizure frequency, (ii) drugs in use, and (iii) degree of ketosis. ResultsAfter 12 weeks on the diet, we found a significant reduction in T3 and fT3 values (13.4% and 10.6%, respectively) and a significant increase in fT4 values (12.1%) compared with baseline. In addition, there was an insignificant increase in TSH and rT3. These changes were similar in women and men, and there was no correlation to drugs in use (enzyme-inducing vs. nonenzyme-inducing drugs), changes in seizure frequency, or level of ketosis. ConclusionThis study indicates that dietary treatment for epilepsy may bring about a modest fall in thyroid hormone levels. This could be relevant for those patients with low thyroid hormones and those treated with ASMs known to lower thyroid hormone levels. A cumulative effect of ASMs, low basal thyroid hormone levels, and ketogenic diet may therefore be of clinical importance in the case of thyroid hormones when treating patients with MAD.

Thyroid Profiles in a Patient with Resistance to Thyroid Hormone and Episodes of Thyrotoxicosis, Including Repeated Painless Thyroiditis

Thyrotoxic disease can be difficult to recognize in patients with resistance to thyroid hormone (RTH) because the clinical symptoms of thyrotoxicosis cannot be observed, and thyrotropin (TSH) may not be suppressed because of hormone resistance. Painless thyroiditis is a relatively common cause of thyrotoxicosis, but its occurrence in RTH has not been reported. We assessed the thyroid profile in a patient with RTH and episodes of thyrotoxicosis who experienced repeated painless thyroiditis. A 44-year-old Japanese woman with RTH, which was confirmed by the presence of a P453A mutation in the thyroid hormone receptor β (TRβ) gene, showed a slight elevation of the basal levels of thyroid hormones, which indicated that her pituitary RTH was mild. She experienced a slight exacerbation of hyperthyroxinemia concomitant with TSH suppression. A diagnosis of painless thyroiditis was made because of the absence of TSH receptor antibodies, low Tc-99m pertechnetate uptake by the thyroid gland, and transient suppression followed by a slight elevation of TSH following the elevation of thyroid hormones. The patient's complaints of general malaise and occasional palpitations did not change throughout the course of painless thyroiditis. Three years later, painless thyroiditis occurred again without any deterioration of the clinical manifestations. Mild pituitary RTH can be overcome by slight exacerbation of hyperthyroxinemia during mild thyrotoxicosis. When pituitary resistance is severe and TSH is not suppressed, thyrotoxicosis may be overlooked.

A Rise in Haemoglobin Levels May Enhance Serum Triiodothyronine (T3) Concentrations in Prepubertal Patients with ß-Thalassaemia Major

The aim of the present study was to investigate the effects of increased haemoglobin (Hb) levels on the thyroid function in patients with beta-thalassaemia major. Basal levels of thyroid hormones (T4, T3) and free thyroid hormones (fT4, fT3), basal TSH concentrations and the TSH responses to a TRH bolus (0.2 mg iv) were studied in ten euthyroid thalassaemic patients, aged 8 to 19 years, and in one 12 years-old thalassaemic girl with primary hypothyroidism. Five euthyroid thalassaemic patients (aged 8 to 12 years), as well as the hypothyroid thalassaemic girl, were prepubertal, whereas five euthyroid thalassaemic patients (aged 15 to 19 years) had delayed puberty. In each patient, the endocrine evaluation was carried out under conditions of low Hb levels (31 days after the last blood transfusion, mean Hb = 9.8 +/- 1.5 g/dl), and 11 days after the transfusion of 2 units packed red blood cells (PRBC). The latter increased significantly Hb concentrations in all the thalassaemic patients (mean Hb = 12.8 +/- 2.5 g/dl, P less than 0.001). Twelve normal prepubertal subjects, aged 6 to 11 years, served as the control group. Before the PRBC transfusion, basal T4, T3, fT4, fT3 and TSH concentrations were similar in euthyroid prepubertal thalassaemic patients (EPT) and in euthyroid patients with delayed puberty (EDPT), and were comparable to those in control subjects. The TSH responses to TRH (TSH peak, area and delta area) observed in EPT patients were similar to those in the EDPT group, but significantly higher in comparison with the normal children.(ABSTRACT TRUNCATED AT 250 WORDS)

Función tiroidea en pacientes pediátricos con enfermedad renal crónica

Thyroid Function in Pediatric Patients with Chronic Renal Failure Objective: To characterize the thyroid function in mild (L), moderate (M), hemodialysis (HD), peritoneal dialysis (PD), chronic renal failure (CRF) and post kidney transplant (TX). Method: 46 children between 9.3 ± 3.7 years-old with CRF (10 mild (L), 10 moderate (M), 10 peritoneodialysis (PD), 6 hemodialysis (HD), 10 transplants (TX)) were evaluated. Basal total T4 and free T3, TRH test (TSH at 0-30-60 min), creatinine, BUN, creatinine clearance and anthropometric parameters were measured. The statistics analysis included Anova Test to compare group results and correlation coefficients for studied variables. Results: Basal thyroid hormone levels were normal in all groups and no differences between groups (except higher TSH in L (p < 0.01)) were found. TRH test response was prolonged on L, M, PD and HD and deficient in TX, except 3 TX patients who had normal TRH response, all using Tacrolimus, Micofenolate and Prednisone on alternate day treatment versus the remaining TX who where on Cyclosporine or Azathioprine, Micofenolate and continuous corticoid regimen. Prolonged TRH response correlates with creatinine (p < 0.001) and creatinine clearance (p < 0,01). Conclusions: Basal thyroid hormones were normal in all groups. TRH test response was predominantly prolonged in L, M, PD and HD, suggesting adaptative phenomena at tertiary level, and correlates with renal function. TX patients had deficient TRH response, suggesting hypofisial dysfunction. (Key words: TRH test, thyroid, chronic renal failure, children). Rev Chil Pediatr 2008; 79 (3): 259-266

Thyroid function testing in elephant seals in health and disease

Northern Elephant Seal Skin Disease (NESSD) is a severe, ulcerative, skin condition of unknown cause affecting primarily yearling northern elephant seals ( Mirounga angustirostris); it has been associated with decreased levels of circulating thyroxine (T 4) and triiodothyronine (T 3). Abnormalities of the thyroid gland that result in decreased hormone levels (hypothyroidism) can result in hair loss, scaling and secondary skin infections. However, concurrent illness (including skin ailments) can suppress basal levels of thyroid hormones and mimic hypothyroidism; when this occurs in animals with normal thyroid glands it is called “sick euthyroid syndrome”. The two conditions (true hypothyroidism vs. “sick euthyroid”) can be distinguished in dogs by testing the response of the thyroid gland to exogenous thyrotropin (Thyroid Stimulating Hormone, TSH). To determine whether hypothyroidism is involved in the etiology of NESSD, we tested thyroid function of stranded yearling elephant seals in the following categories: healthy seals (rehabilitated and ready for release; N = 9), seals suffering from NESSD ( N = 16) and seals with other illnesses (e.g., lungworm pneumonia; N = 10). Levels of T 4 increased significantly for all three categories of elephant seals following TSH stimulation, suggesting that seals with NESSD are “sick euthyroid” and that the disease is not associated with abnormal thyroid gland function.

Association between thyroid autoimmunity and fibromyalgic disease severity

Our objectives were to investigate thyroid abnormalities and autoimmunity in 120 patients affected by fibromyalgia (FM) and to study their relationships with clinical data and symptoms. Thyroid assessment by means of antithyroglobulin antibodies, antithyroid peroxidase antibodies, free triiodo-thyronine, free thyroxine, and thyroid stimulating hormone analyses was carried out. The clinical parameters "Fibromyalgia Impact Questionnaire", pain, tender points, fatigue, and other symptoms, and the presence of depression or anxiety disorders were evaluated. The basal thyroid hormone levels of FM patients were in the normal range, while 41% of the patients had at least one thyroid antibody. Patients with thyroid autoimmunity showed a higher percentage of dry eyes, burning, or pain with urination, allodynia, blurred vision, and sore throat. Correlations found between thyroid autoimmunity and age or with the presence of depression or anxiety disorders were not significant. However, in the cohort of post-menopausal patients, the frequency of thyroid autoimmunity was higher with respect to pre-menopausal patients. In conclusion, autoimmune thyroiditis is present in an elevated percentage of FM patients, and it has been associated with the presence of typical symptoms of the disease.

Thyroid hormone levels and recurrence of major depression.

The relationship between basal thyroid hormone levels and acute antidepressant response has been studied, but any relationship between basal thyroid hormone levels and long-term course of depressive illness has not been evaluated. The authors used a Cox regression survival analysis to evaluate the relationship between life course of depressive illness and basal levels of thyroid hormones (triiodothyronine [T(3)], thyroxine [T(4)], and thyrotropin) in 75 outpatients with unipolar major depressive disorder. Time to recurrence of major depression was inversely related to T(3) levels but not to T(4) levels. These data may be of clinical interest in view of the fact that T(3) is used to augment antidepressant response.

Electrodermal Activity in Nonmedicated Hyperthyroid Patients Having No Depressive Symptoms

The aim of the present study was to investigate whether the alteration in hypothalamic–pituitary–thyroid axis function results in electrodermal abnormality without causing marked psychiatric manifestations or not. Electrodermal activity was recorded with the skin conductance unit and IBM-AT computer. Basal levels of electrodermal activity (EDA), as well as responsivity to repeated insignificant acoustic stimulation were studied in 24 nonmedicated hyperthyroid patients and 35 healthy controls. The outcome of psychiatric rating scores indicated that patients had low anxiety scores and normal depression scores. The basal levels of thyroid hormones were higher in patients, when compared with the control group. On the analysis of EDA, we found lower onset latency and duration of the skin conductance response and higher skin conductance level in nonmedicated patients than healthy controls. The results above provide supporting evidence that the change of hypothalamic–pituitary–thyroid axis function results in abnormal EDA, without causing marked psychiatric manifestations.

Basal Thyroid Indices in Adolescent Depression and Bipolar Disorder

Abnormalities of the thyroid axis are documented in adult mood disorders. The most consistent findings have been observed in major depressive disorder with elevations of thyroxine (T4) or free-T4 (fT4) within the euthyroid range that decrease with treatment. The literature on adolescents is limited, and it is unknown whether similar findings might be present in this population. First admissions to a university hospital adolescent psychiatry unit were reviewed. Fourteen depressed and 13 manic patients satisfied inclusion and exclusion criteria. None had a history of thyroid illness or medical illness or were taking medications known to affect thyroid function. Basal serum thyrotropin, T4, fT4, triiodothyronine (T3), reverse-T3, free thyroxine index (FTI), and T3 resin uptake levels were compared with those of a group of adolescent normal controls. T4 (but not fT4) was elevated in depressed and manic patients compared with controls (p < .05). In manic patients, T3 was decreased and reverse-T3 was increased (p < .05). There were no significant differences in relation to age, sex, or suicidality. We observed significant differences in basal thyroid hormone levels in depressed and manic adolescents. Our results suggest the presence of abnormalities of thyroid function in adolescent mood disorders similar to those described in mood-disordered adults.

Electrodermal activity in relation to basal and postdexamethasone levels of thyroid stimulating hormone and basal levels of thyroid hormones in major depressive patients and healthy subjects

Electrodermal activity in 50 patients with major depression and 50 matched healthy control subjects was related to basal and postdexamethasone changes in levels of thyroid stimulating hormone (TSH), basal levels of thyroid hormones, and nocturnal levels of urinary cortisol. Levels of skin conductance and thyroxine were inversely correlated in the patients, but positively correlated in the healthy subjects. Patients with blunted postdexamethasone reduction of TSH showed high rates of nonevoked electrodermal fluctuations, low TSH levels, and elevated nocturnal urinary cortisol levels.

Sheehan's syndrome: clinical profile, pituitary hormone responses and computed sellar tomography.

Twenty patients with the typical clinical presentation of Sheehan's syndrome were studied. All had a severe degree of hypopituitarism. The circulating mean basal levels of thyroid hormones, cortisol and prolactin were significantly lower (p < 0.05 to < 0.02) compared to those in 50 age matched controls. The provoked pituitary responses to combined pituitary stimulation in 13 patients were markedly lower (p < 0.02 to < 0.001) than those in ten age matched control subjects. Sellar computed tomography revealed an empty sella in all the patients; partial in five and complete in the remaining. A secondary empty sella is considered a characteristic finding in the classical form of Sheehan's syndrome.

Alteration by prolonged oral administration of a thyrotropin-releasing hormone analog, TA-0910, of the pituitary-thyroid axis in subjects with brain stroke.

We evaluated whether prolonged oral administration of a novel analog of thyrotropin-releasing hormone (TRH), TA-0910, may change the pituitary-thyroid axis in human subjects with brain stroke. The subjects were given one oral dose of 2.5-20 mg of TA-0910 daily for 8 weeks, and then blood levels of TA-0910, thyroid hormones and thyrotropin (TSH) were measured. Plasma levels of TA-0910 were elevated with increasing doses. After administration of TA-0910, the basal levels of thyroid hormones and TSH had a tendency to increase and decrease, respectively, but those changes remained in the normal range. The secretion of TSH in response to TRH was not significantly affected by TA-0910 administration. No significant changes in other pituitary hormones were observed after TA-0910 administration. The present data indicate that prolonged oral administration of TA-0910 did not significantly alter the pituitary-thyroid axis in subjects with brain stroke.

The thyroid and melancholia

Several studies that have examined heterogeneous groups of patients suggest that altered thyroid function may distinguish melancholic from nonmelancholic depression. We therefore measured basal thyroid hormone levels in 90 unipolar depressed patients who were divided into melancholic and nonmelancholic subgroups according to three definitions. Levels of thyroxine, triidothyronine, and thyrotropin, obtained using an ultrasensitive assay, did not distinguish the subtypes of depression. However, severity of depression contributed significantly to the difference between these subtypes according to DSM-III and Research Diagnostic Criteria.

A Perspective on the Thyroid and Depression*

There is extensive literature documenting an association between abnormalities of the hypothalamic-pituitary-thyroid axis and disorders of mood. However, the specific abnormality in thyroid functioning associated with primary affective disorder remains poorly understood. Various aspects of the relationship between thyroid functioning and affective illness are reviewed. Particular attention is paid to psychiatric symptoms and clinical thyroid disorders as well as abnormalities of basal thyroid hormone levels in depression and the use of thyroid hormones in the treatment of depressive illness. Current hypotheses regarding the association between altered thyroid functioning and depressive illness are critically reviewed.

The Effect of Tricyclic Antidepressants on Basal Thyroid Hormone Levels in Depressed Patients

The effect of tricyclic antidepressant treatment on basal thyroid hormone levels was evaluated in 28 subjects with primary major depression. In the total group, tricyclic antidepressant treatment was associated with significant reductions in measures of thyroxine. Furthermore, responders to antidepressant treatment had significantly greater decrements in thyroxine and the free thyroxine index as compared with nonresponders. This finding appears consistent with the effects of a wide range of antidepressant treatments on thyroid function tests.

Thyroid Function in Heifers Measured by Hormone Levels before and after Injection of Thyrotropin Releasing Hormone

Abstract Thyroid hormone levels before and after thyrotropin releasing hormone (TRH) injection were compared at four different stages in relation to parturition in nine heifers. Basal thyroxine (T4) levels were similar before conception and two weeks before calving, but the T4 responses to TRH were reduced near parturition. Hormone levels and responses were low 2 weeks as well as three months after parturition. Both basal levels of T3 and T3 responses to TRH were low near parturition. Three months after parturition both basal level and TRH responses were comparable to those observed before conception. Low basal levels of thyroid hormones near parturition were not associated with an increased disappearance rate. Reduced thyroid secretion activity during early lactation must be the main explanation for the low thyroid hormone levels seen at this stage.

Serotonergic and catecholaminergic influence on thyroid function in the vervet monkey

Vervet monkeys were pharmacologically treated acutely and with repeated dose loading to alter serotonergic systems to assess the role of serotonin in the regulation of the hypothalamus-pituitary-thyroid axis. Acute L-tryptophan administration failed to alter basal levels of thyroid hormones but did decrease the TRH-induced TSH response. Repeated dose loading of tryptophan or 5-hydroxytryptophan increased blood serotonin and plasma T3 and decreased plasma TSH. The tryptophan hydroxylase inhibitor p-chlorophenylalanine yielded decreased blood serotonin, but did not affect plasma TSH, T4 or T3. The monoamine oxidase inhibitor chlorgyline also resulted in increased blood serotonin, but increased plasma TSH and T4 and decreased T3. These data may be explained by a unitary hypothesis involving central catecholaminergic, rather than serotonergic, control of TRH release. Chlorgyline may produce its effects predominantly by facilitating catecholaminergic stimulation of TRH release resulting in increased TSH and a consequent increase in T4. It is suggested that the effects of tryptophan and 5-hydroxytryptophan result from increases in serotonin levels in the thyroid gland to produce an increase in T3 with a compensatory decrease in TSH via negative feedback. The differences observed between the acute and repeated dose loading studies stress the need for both types of studies before drawing conclusions about the effects of pharmacological manipulations on hormonal levels.