Results. In cross-sectional analysis, the relationship between. TSH and fT4 was not log-linear but a combination of sigmoidal curves. The rate of change of TSH. Relationship between TSH and free T4 in subjects not receiving thyroxine treatment. The median TSH for each free T4 integer value is represented (‚). The UQs. FT4 and TSH, relation to diagnoses in an unselected psychiatric acute-ward population, and change during acute psychiatric admission.
For patients, data for FT4 were available at both admittance and discharge, and the corresponding number for TSH was patients. Results A significantly higher share of patients had higher levels of FT4 and TSH at admittance than expected for healthy individuals. No significant effect of gender or most diagnostic groups was seen.
For female patients with substance-use disorder SUDthe level of TSH was significantly lower than that for all other diagnostic groups.
For the population with available markers at both admittance and discharge, in total, there was a significant reduction of FT4 from admittance to discharge, not followed by any change in TSH. FT4 is normalized during the inpatient stay independently of TSH.
This indicates somatic effects of psychiatric stress that may be of clinical importance and the phenomenon should be further explored. Thus future studies on thyroid activity in psychiatric patients should focus on function and level of stress and suffering rather than diagnostic groups.What is Thyroid Profile Test: T3/Free T3,T4/ Free T4 ,TSH :Normal Range &Interpretation -Dr Kasi MD
Electronic supplementary material The online version of this article Although it is established that hypothalamic-pituitary-thyroid HPT axis abnormalities may be associated with psychiatric pathophysiology [ 2 — 4 ], the HPT pattern in psychiatric patients with non-thyroidal illness is still inconsistent. Altered concentrations of free thyroxine FT4 have been described in patients with psychiatric disorders such as schizophrenia and affective disorders [ 35 — 8 ], but findings are inconsistent; for example, other reports on personality disorder and alcoholism are negative [ 6 ].
The relationship between serum TSH and free T4 in older people.
In addition, an association between thyroid hormones within reference range and cognitive dysfunction in older people has been indicated [ 1 ]. In a cross-sectional, retrospective study, we analyzed TSH and free T4 results from subjects collected over 12 years by a single laboratory.
For each free T4 value in picomoles per literthe median TSH was calculated and analyzed by sex and age in year bands. The relationship between log TSH and free T4 was nonlinear.
Thyroid Gland Function Tests
The TSH—free T4 relationship is not inverse log-linear but can be described by 2 overlapping negative sigmoid curves. At physiological free T4 concentrations, TSH is higher in men and in older people, whereas the TSH response to hypothyroidism is more robust in younger people.
These results advance understanding of the TSH—free T4 relationship, which is central to thyroid pathophysiology and laboratory diagnosis of thyroid disease. In healthy individuals, homeostatic mechanisms ensure that circulating concentrations of TSH and T4 are tightly regulated.
The relationship between serum TSH and free T4 in older people.
Repeated measures of TSH and T4 in healthy subjects reflecting intraindividual variation fall within a narrower range than that for a population interindividual variation 12leading to the concept that each person has a unique set point for hypothalamo-pituitary-thyroid HPT axis function 1 — 3.
The HPT set point reflects, in part, the characteristics of each individual's negative feedback loop, including the responsiveness of thyroid follicular cells to TSH stimulation and the sensitivity of TRH neurons and thyrotropes to thyroid hormone feedback. In studies of hypothyroid individuals treated with varying doses of thyroxine, the relationship between serum TSH and T4 appeared hyperbolic when plotted on linear graph coordinates 5whereas when TSH was plotted on a logarithmic log scale, it was approximately linear 46.
Similar results have been reported from studies of thyroid hormone loading in euthyroid subjects 237. InSpencer et al 7 reported an inverse, linear relationship between log TSH and free T4 index in a cross-sectional analysis of ambulatory individuals with a wide range of thyroid function tests; this has since become a generally accepted tenet of thyroid physiology.
Perhaps surprisingly, the log-linear relationship between TSH and T4 has not been reassessed in large epidemiological studies until recently. In an analysis of 2 datasets comprising and patients referred for thyroid function testing, Hoermann et al 8 found that the relationship between log TSH and free T4 was, in fact, not linear; rather it was a complex relationship with at least 3 distinct segments.
The Relationship between Serum TSH and Free T4 Is Not Log-Linear and Varies by Age and Sex
Similar results were reported by Clark et al 9 in a cross-sectional analysis of individuals in whom the TSH—free T4 relationship was not linear but was best described as a fourth-order polynomial.
Both these studies had limitations: Nonlinear quantile regression models were used to assess relationships between serum TSH and free T4 values, with age and sex as covariates.
The relationship was not linear, but rather was best described by two negative sigmoid curves.
Among patients taking L-T4, the relationship was similar. Median serum TSH values were higher for males than for females 3. Median TSH was higher in men than in women at almost every free T4 value, with more extreme differences in the upper part of the reference range.
Among euthyroid individuals, TSH was higher in men and increased with advancing age.
The rise in TSH with overt hypothyroidism is attenuated in older adults. Importantly, it is possible that the lack of a log-linear relationship between TSH and free T4 was merely an artifact due to inadequacies of the free T4 assay used.
Future studies could conduct similar analyses using different free T4 assay methods, in particular the gold standard methods of equilibrium dialysis or isotope-dilution liquid chromatography with tandem mass spectroscopy. What relevance do these results have for clinical practice? These data suggest that TSH reference ranges are not one-size-fits-all, and the use of a single TSH range for all subpopulations might result in misclassification of thyroid status in some cases, in particular the inappropriate diagnosis of subclinical hypothyroidism.
The age-associated increase in serum TSH among euthyroid individuals seen in this and previous studies 4 argues against routine treatment of mild TSH elevations in elderly patients.