Though in the euthyroid group pre-estrogen therapy serum TSH levels 1. In the hypothyroid group, serum TSH increased from 0. Since it is known 9 that the thyrotrops have estrogen receptors, though not as abundant as other anterior pituitary cell types, and in view of literature on TSH responsiveness to E2 10 — 12 , we can elaborate a hypothesis for our findings in the two patients.
In ovariectomized rats, increasing serum estrogen levels within the physiological range increase both basal and TRH-stimulated TSH release as well as PRL release 10 , We hypothesize that a robust E2-driven TSH release at mid-cycle with consequent elevation of serum TSH may result from either a robust circulating E2 peak and associated hyper-response of the E2 receptors in the thyrotrops or increased sensitivity of E2 receptors to less robust circulating E2 levels.
However, additional mechanism cannot be excluded. These mechanisms include the E2-driven i inhibition of the negative feedback that thyroid hormones exert on both basal and TRH-stimulated TSH release 12 , ii induction of TRH receptors in the pituitary 13 , and iii decreased TRH degradation In conclusion, a large prospective study is required to know the proportion of reproductive age women, under L-T4 replacement therapy, with elevation of serum TSH due to mid-cycle blood sampling.
Once confirmed, our observations may have important implications for diagnosis and management of thyroid disease, and may call for standardization of serum TSH measurement outside of periovulatory days.
This study was carried out with written informed consent from all subjects. All subjects gave written informed consent in accordance with the declaration of Helsinki. This study did not require submission to Ethical Committee. SB collected data. All the authors contributed equally to the writing of the manuscript and approved the final version. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Benvenga S. When thyroid hormone replacement is ineffective? Curr Opin Endocrinol Diabetes Obes — Morris JC.
How do you approach the problem of TSH elevation in a patient on high-dose thyroid hormone replacement? Clin Endocrinol Oxf —3. Some slight variation in test results is normal and nothing to worry about, according to the ATA, but more significant variations could indicate the need for a dosage change. These are factors that can affect your thyroid levels :.
You get tested at different times of the day. Thyroid hormone levels tend to go up at night and down during the day, according to the ATA. However, this variation is very slight, says Terry F. You go to different labs for testing. Results may vary from lab to lab, but even if you go to the same lab, your results can vary from test to test, the ATA says. The lab may get one reading on one occasion and a slightly higher or lower reading the next. You switch brands.
A number of companies manufacture thyroid hormone, and their products are slightly different from each other. Your body can react differently to the different brands. You skip pills. Although the medication you take — T4 thyroxine , the main hormone made by the thyroid — stays in your blood a long time, missing a few days in a row, or consistently missing now and then over time, could affect your test results, says Norma Lopez, MD , an associate professor of endocrinology at the Stritch School of Medicine at Loyola University Chicago.
You take the wrong dosage. Say you are scheduled to take micrograms mcg a week mcg once a day but miss two pills and end up taking only mcg. This means there are times of the day when it naturally higher or lower. Researchers tested the blood of hypothyroid subjects both before 8 a. In hypothyroid patients both untreated and on thyroid medication, TSH dropped was substantially lower during the afternoon test.
This means an estimated 50 percent of people with hypothyroidism are not being diagnosed. In the untreated group, TSH was 5. In the treated group, TSH was 3. This means even a late morning blood draw could result in a failure to diagnose. Table 2 Comparison of free thyroxine and thyroid-stimulating hormone values by different assay methods. Limitations In our study, we studied the levels of TSH 2 h postmeal.
Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. Physiological regulation of circadian and pulsatile thyrotropin secretion in normal man and woman. J Clin Endocrinol Metab. Circadian and circannual rhythms in thyroid hormones: Determining the TSH and free T4 reference intervals based upon time of day, age, and sex.
The hour plasma thyrotrophin profile. Clin Sci. Subclinical thyroid disease: Clinical applications. Management of thyroid dysfunction during pregnancy and postpartum: An Endocrine Society clinical practice guideline. Does fasting or postprandial state affect thyroid function testing? Serum TSH variability in normal individuals: The influence of time of sample collection.
Morley JE. Neuroendocrine control of thyrotropin secretion. Endocr Rev. Circulating somatostatin is not a physiologic regulator of gastric acid production in man. Eur J Clin Invest. Support Center Support Center.
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