Thyroid-stimulating Hormone Threshold Research Articles

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Neonatal Thyroid-Stimulating Hormone Concentrations in Belgium: A Useful Indicator for Detecting Mild Iodine Deficiency?

It has been proposed that neonatal thyroid-stimulating hormone (TSH) concentrations are a good indicator of iodine deficiency in the population. A frequency of neonatal TSH concentrations above 5 mU/L below 3% has been proposed as the threshold indicating iodine sufficiency. The objective of the present study was to evaluate feasibility and usefulness of nation-wide neonatal TSH concentration screening results to assess iodine status in Belgium. All newborns born in Belgium during the period 2009–2011 (n = 377713) were included in the study, except those suffering from congenital hypothyroidism and premature neonates. The frequency of neonatal TSH concentrations above 5 mU/L from 2009 to 2011 in Belgium fluctuated between 2.6 and 3.3% in the centres using the same TSH assay. There was a significant inverse association between neonatal TSH level and birth weight. The longer the duration between birth and screening, the lower the TSH level. Neonatal TSH levels were significantly lower in winter than in spring or autumn and significantly lower in spring and summer than in autumn while significantly higher in spring compared to summer. In conclusion, despite that pregnant women in Belgium are mildly iodine deficient, the frequency of neonatal TSH concentrations above 5 mU/L was very low, suggesting that the neonatal TSH threshold proposed for detecting iodine deficiency needs to be re-evaluated. Although neonatal TSH is useful to detect severe iodine deficiency, it should not be recommended presently for the evaluation of iodine status in mildly iodine deficient regions.

Recurrent IVF failure: other factors

IVF failure is a problem for a couple in the singular but can be a tragedy in the plural. Recurrent IVF failure has multiple known causes but many which are not routinely considered as part of the posttreatment analysis. The reason is there are several causes associated with lifestyle and other causes related to pre-existing conditions that have only a tenuous or no apparent connection to fertility. This article examines the impact of obesity, cigarette smoke, uterine anatomy, body mass index, thyroid dysfunction, immune factors, the hereditary and acquired thrombophilias, and embryo transfer technique on recurrent IVF failure.

Thyroid dysfunction in pregnancy

Timely treatment of thyroid disease during pregnancy is important in preventing adverse maternal and fetal outcomes. Thyroid abnormalities are very often subclinical in nature and not easily recognized without specific screening programs. Even mild maternal thyroid hormone deficiency may lead to neurodevelopment complications in the fetus. The main diagnostic indicator of thyroid disease is the measurement of serum thyroid-stimulating hormone and free thyroxine levels. Availability of gestation-age-specific thyroid-stimulating hormone thresholds is an important aid in the accurate diagnosis and treatment of thyroid dysfunction. Pregnancy- specific free thyroxine thresholds not presently available are also required. Large-scale intervention trials are urgently needed to assess the efficacy of preconception or early pregnancy screening for thyroid disorders. Accurate interpretation of both antepartum and postpartum levels of thyroid hormones is important in preventing pregnancy-related complication secondary to thyroid dysfunction. This article sheds light on the best ways of management of thyroid dysfunction during pregnancy in order to prevent any possible maternal or fetal complication.

Further Studies on Delineating Thyroid-Stimulating Hormone (TSH) Reference Range

The aim of the study was to evaluate thyroid-stimulating hormone (TSH) concentration in a reference group and to compare it with the TSH in subjects with high probability of thyroid dysfunction. The study population consisted of 852 subjects. The reference group consisting of 316 subjects was obtained by the exclusion of the subjects having thyroid disease, taking thyroid influencing drugs, having increased thyroid peroxidase (TPO) antibodies, or having abnormal thyroid ultrasound. 42 high probability of thyroid dysfunction subjects were defined by the association of increased TPO antibody concentration, changed echogenicity, and changed echosonographic structure of thyroid parenchyma. In the reference group TSH reference range was 0.45 mU/l (95% CI 0.39-0.56 mU/l) to 3.43 mU/l (95% CI 3.10-4.22 mU/l). To distinguish reference and high probability of thyroid dysfunction group a TSH threshold was calculated. At a threshold value of 3.09 mU/l (95% CI 2.93-3.38 mU/l), specificity was 95% and sensitivity 38.1%. Using 2 different approaches to find upper limit of the TSH reference range we obtained similar results. Using reference group only a value of 3.43 mU/l was obtained. Using both reference group and subjects with the high probability of thyroid dysfunction we obtained 95% CI for the upper reference limit between 2.93 and 3.38 mU/l. Based on these premises, it could be argued that conservative estimate of the TSH upper reference range should be 3.4 mU/l for both sexes.

What is a normal thyroid stimulating hormone (TSH) level? Effects of stricter TSH thresholds on pregnancy outcomes after IVF

OBJECTIVE: To determine if there was a difference in pregnancy outcomes of IVF patients using diagnostic thresholds of TSH of 2.5 or 4.5mU/L. DESIGN: Retrospective cohort study. MATERIALS AND METHODS: Outcomes from the first cycle of all fresh IVF patients with an embryo transfer from 2005-2008 within 1 yr of TSH screening at a single center were studied. Patients with hyperthyroidism (TSH<0.40), hyperprolactinemia, cycles using donor oocyte, PGD, or those lacking delivery follow-up were excluded. Clinical endpoints were rates of clinical pregnancy (gestational sac), miscarriage (loss after gestational sac), and live birth. RESULTS: We identified 1,055 patients with an average age of 36.7 ± 4.8 years with a mean TSH of 2.1 ± 1.6 (median 3.9; range 0.4-23.8). There was no correlation between patient age and TSH, and no difference in ages between abnormal and normal TSH groups using either threshold. TSH thresholds of ≥2.5mU/L resulted in classification of 24% of patients as abnormal (normal: median, interquartile range 1.5, 1.2-1.9mU/L vs. abnormal: 3.2, 2.8-3.8mU/L). TSH thresholds of ≥4.5mU/L resulted in classification of 5.3% of patients as abnormal (normal: 1.7, 1.3-2.3mU/L vs. abnormal: 5.1,4.4-6.7mU/L.) There was no difference in the clinical pregnancy rate with TSH >2.5 vs. <2.5mU/L (52% vs. 47%), live delivery (39% vs. 34%), or miscarriage rates (13% vs 13%). With TSH > 4.5 vs. <4.5mU/L, there was no difference in the clinical pregnancy rate (54% vs. 48%), live delivery (43% vs. 34%), or miscarriage rates (9% vs. 13%). CONCLUSION: While lowering the TSH threshold to 2.5mU/L would result in a nearly 5-fold increase in the number of women being classified as abnormal, no difference in the rates of clinical pregnancy, delivery, or miscarriage were observed. The lack of differences in clinical outcomes using a lower TSH threshold contributes to the current debate on the relative merits of screening, of lowering the upper limit of normal for TSH, and the utility of treating subclinical hypothyroidism.

What is a normal thyroid-stimulating hormone (TSH) level? Effects of stricter TSH thresholds on pregnancy outcomes after in vitro fertilization

Using a thyroid-stimulating hormone (TSH) cutoff of 2.5 mIU/L or 4.5 mIU/L, no differences in the rates of clinical pregnancy, delivery, or miscarriage were observed in this large, retrospective cohort study of first-cycle IVF patients from 2005 through 2008, after controlling for age. Although lowering the TSH threshold to 2.5 mIU/L would result in a nearly fivefold increase in the number of women being classified as hypothyroid, the lack of differences in maternal clinical outcomes must be considered in the current controversy regarding the relative merits of lowering the upper limit of normal of TSH.

Thyroid-stimulating hormone is associated with insulin resistance independently of body mass index and age in women with polycystic ovary syndrome

The aim of this study was to evaluate the association between thyroid function, reflected by thyroid-stimulating hormone (TSH) levels, and insulin resistance (IR) in 337 women suffering from polycystic ovary syndrome (PCOS). Clinical, metabolic and endocrine parameters were obtained and an oral glucose tolerance test was performed, with calculation of IR indices. The association between thyroid function and IR was evaluated with classification analysis using logistic regression and 10-fold cross-validation to identify a possible TSH threshold for IR. Parameters were then compared between women above and below the TSH threshold using two-sample tests. One-way analyses of covariance were performed to explore whether the impact of TSH on IR is independent of other variables. A TSH cut-off value around 2 mIU/l had the best sensitivity and specificity for identifying women with IR. Women with TSH >or= 2 mIU/l were younger, had a higher body mass index (BMI) and were more insulin-resistant compared with women with TSH < 2 mIU/l. This effect of TSH on IR was independent of age and BMI. In women with PCOS, a significant association between thyroid function, as reflected by TSH >or= 2 mIU/l, and IR was found and the association appeared to be independent of age and BMI.

Repeat testing for congenital hypothyroidism in preterm infants is unnecessary with an appropriate thyroid stimulating hormone threshold

Background:Revised UK neonatal screening guidelines recommend that a second blood sample for assay of thyroid stimulating hormone (TSH) be taken when preterm infants reach a postmenstrual age of 36 weeks.Objective:To...

Does Treating Subclinical Hypothyroidism Improve Markers of Cardiovascular Risk?

Subclinical hypothyroidism is defined as an elevated serum thyroid-stimulating hormone (TSH) level in the face of normal free thyroid hormone values. The overall prevalence of subclinical hypothyroidism is 4-10% in the general population and up to 20% in women aged >60 years. The potential benefits and risks of therapy for subclinical hypothyroidism have been debated for 2 decades, and a consensus is still lacking. Besides avoiding the progression to overt hypothyroidism, the decision to treat patients with subclinical hypothyroidism relies mainly on the risk of metabolic and cardiovascular alterations. Subclinical hypothyroidism causes changes in cardiovascular function similar to, but less marked than, those occurring in patients with overt hypothyroidism. Diastolic dysfunction both at rest and upon effort is the most consistent cardiac abnormality in patients with subclinical hypothyroidism, and also in those with slightly elevated TSH levels (>6 mIU/L). Moreover, mild thyroid failure may increase diastolic blood pressure as a result of increased systemic vascular resistance. Restoration of euthyroidism by levothyroxine replacement is generally able to improve all these abnormalities. Early clinical and autopsy studies had suggested an association between subclinical hypothyroidism and coronary heart disease, which has been subsequently confirmed by some, but not all, large cross-sectional and prospective studies. Altered coagulation parameters, elevated lipoprotein (a) levels, and low-grade chronic inflammation are regarded to coalesce with the hypercholesterolemia of untreated patients with subclinical hypothyroidism to enhance the ischemic cardiovascular risk. Although a consensus is still lacking, the strongest evidence for a beneficial effect of levothyroxine replacement on markers of cardiovascular risk is the substantial demonstration that restoration of euthyroidism can lower both total and low-density lipoprotein-cholesterol levels in most patients with subclinical hypothyroidism. However, the actual effectiveness of thyroid hormone substitution in reducing the risk of cardiovascular events remains to be elucidated. In conclusion, the multiplicity and the possible reversibility of subclinical hypothyroidism-associated cardiovascular abnormalities suggest that the decision to treat a patient should depend on the presence of risk factors, rather than on a TSH threshold. On the other hand, levothyroxine replacement therapy can always be discontinued if there is no apparent benefit. Levothyroxine replacement therapy is usually safe providing that excessive administration is avoided by monitoring serum TSH levels. However, the possibility that restoring euthyroidism may be harmful in the oldest of the elderly population of hypothyroid patients has been recently raised, and should be taken into account in making the decision to treat patients with subclinical hypothyroidism who are aged >85 years.

The thyrotropin-releasing hormone stimulation test: A methodological study

Repeated thyroid-stimulating hormone (TSH) determinations were carried out for 90 or 180 minutes following thyrotropin releasing hormone (TRH) stimulation in 160 euthyroid psychiatric patients, most of whom had a symptomatic affective disorder. The purpose was to determine which of the simple TSH measurements from the TRH stimulation test (TRH-ST) yield(s) the most accurate index of pituitary TSH reserves and to clarify the relationship between the various TRH-ST methods reported in the literature. The area beneath the 180 minute TSH response curve, the best available parameter of pituitary TSH stores, was calculated and compared to simple indices of absolute TSH level and increase from 0 minute baseline. Fourteen parameters of the TSH response were determined; TSH 0, TSH 15, TSH 30, and TSH 45 represent the absolute levels at 0, 15, 30, and 45 minutes after TRH administration, respectively. TSH Max is the maximum TSH level attained after TRH infusion among all TSH measures. Δ TSH measures are the increase in TSH relative to baseline. The Δ Max TSH and Δ TSH 30 were highly correlated with the ideal index of pituitary TSH reserve (0 – 180 minute area). Subjects were classified as either blunted or normal over a broad range of Δ Max TSH criteria or thresholds. The number of misclassified subjects (false positives) at each criterion was counted for each of the seven possible combinations of Δ TSH 15, Δ TSH 30, and/or Δ TSH 45. The simplest index which produced the smallest number of false positives was Δ TSH 30 whereas Δ Max TSH (15, 30, and 45) produced no false positives. Overall, Δ TSH 30 was a very good simple index of pituitary TSH stores. This may be the preferred index when economy of time, expense, or blood samples is desired. However, it results in 5–7% false positives, which will compromise specificity somewhat. The preferred simple index of pituitary TSH reserves when accuracy is of highest priority is Δ Max TSH (15, 30, and 45). These data reveal that the TRH-ST can be simplified to include only four TSH levels: TSH 0, TSH 15, TSH 30, and TSH 45.