Increases in Thyrotropin Within the Near-Normal Range Are Associated With Increased Triiodothyronine But Not Increased Thyroxine in the Pediatric Age Group (original) (raw)
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In thyroid health, the pituitary hormone thyroid-stimulating hormone (TSH) raises glandular thyroid hormone production to a physiological level and enhances formation and conversion of T4 to the biologically more active T3. Overstimulation is limited by negative feedback control. In equilibrium defining the euthyroid state, the relationship between TSH and FT4 expresses clusters of genetically determined, interlocked TSH–FT4 pairs, which invalidates their statistical correlation within the euthyroid range. Appropriate reactions to internal or external challenges are defined by unique solutions and homeostatic equilibria. Permissible variations in an individual are much more closely constrained than over a population. Current diagnostic definitions of subclinical thyroid dysfunction are laboratory based, and do not concur with treatment recommendations. An appropriate TSH level is a homeostatic concept that cannot be reduced to a fixed range consideration. The control mode may shift from feedback to tracking where TSH becomes positively, rather than inversely related with FT4. This is obvious in pituitary disease and severe non-thyroid illness, but extends to other prevalent conditions including aging, obesity, and levothyroxine (LT4) treatment. Treatment targets must both be individualized and respect altered equilibria on LT4. To avoid amalgamation bias, clinically meaningful stratification is required in epidemiological studies. In conclusion, pituitary TSH cannot be readily interpreted as a sensitive mirror image of thyroid function because the negative TSH–FT4 correlation is frequently broken, even inverted, by common conditions. The interrelationships between TSH and thyroid hormones and the interlocking elements of the control system are individual, dynamic, and adaptive. This demands a paradigm shift of its diagnostic use.
The impact of the metabolic phenotype on thyroid function in obesity
Diabetology & metabolic syndrome, 2016
Obesity is known to promote mild hyperthyrotropinaemia by unknown metabolic mechanisms. This investigation aimed to explore the association between thyroid function and metabolic phenotype in euthyroid obese individuals. Retrospective, cross-sectional study. Tertiary care center. 952 euthyroid obese individuals referred to our Institution for obesity. Serum levels of TSH, FT4, glucose, insulin and HbA1c levels, lipid profile, liver function and proinflammatory indices were measured. Resting energy expenditure was assessed by indirect calorimetry and body composition by bioimpedance analysis. On admission, 306 patients had previously diagnosed diabetes mellitus on treatment with metformin, while 113 patients were diagnosed with incident diabetes mellitus. Serum TSH levels were similar between metformin-treated diabetic subjects and metformin-untreated subjects, while FT4 was slightly but significantly higher in the former. Analysis stratified by TSH categories found no effect of metf...
The Journal of clinical endocrinology and metabolism, 2016
Thyroid hormones are important developmental factors and levels should be adequate both in the pregnant woman and in the fetus. However, there is no consensus on maternal thyroid test reference limits in early pregnancy. Estimation of week-to-week changes in and predictors of TSH and free T4 (fT4) reference limits in the first trimester of pregnancy. Measurement of TSH and fT4 in biobank sera collected in pregnancy weeks 5-19 from a random sample of the Danish National Birth Cohort that enrolled 101 032 pregnant in 1996-2002. National cohort of pregnant women. Healthy participants (n = 6671) were identified and individual characteristics retrieved using interview data and data from Danish national health registers. None. Reference limits for TSH and fT4 in each first trimester pregnancy week and predictors of these reference limits. TSH reference limits were very variable. Up to and including week 6, nonpregnancy reference limits could be used. In weeks 9-12, TSH upper reference lim...
International journal of obesity and related metabolic disorders : journal of the International Association for the Study of Obesity, 1999
To compare insulin-like growth factor-I (IGF-I) concentrations in obese and normal subjects, and evaluate the possible relationships between IGF-I concentrations and demographic, anthropometric, metabolic and hormonal variables in obese patients. 286 obese outpatients (OB, 234 female and 52 male; age 18-71 y, body mass index (BMI) > 27 kg/m2) were recruited. BMI, waist-to-hip ratio (WHR), serum basal and oral glucose tolerance test (OGTT)-stimulated glucose and insulin concentrations, IGF-I, basal growth hormone (GH), prolactin (PRL), androgens, thyrotropin (TSH), free triiodothyronine (fT3), free thyroxine (fT4), free fatty acids (FFA), triglycerides, total and high density lipoprotein (HDL)-cholesterol, 24h-urinary cortisol levels and blood pressure (BP) values were measured. IGF-I concentrations were also evaluated in a large population of 326 age-matched controls (controls, 228 women, 98 men; age 20-86 y, BMI < 25 kg/m2). IGF-I concentrations were lower in OB than in contr...
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