FT4 immunoassays are notoriously unreliable during pregnancy , but relying on TSH is not sufficient in this case.
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During pregnancy, increased hCG can lead to transient hCG-induced thyrotoxicosis. This can be reflected in lower limits of TSH during the first trimester.
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The lower and upper reference limits for serum TSH are decreased by about 0. Of note, in 1. The differences in normal TSH intervals in the various ethnic groups persist during pregnancy ; therefore, providing specific normal ranges for the local population is of particular advantage. Taken together, and in accordance with the new American Thyroid Association guidelines for women in pregnancy, trimester-specific reference intervals for TSH, as defined in populations with optimal iodine intake, should be applied, although they are not generally provided If trimester-specific reference intervals for TSH are not available in the laboratory, the following reference intervals are recommended by the American Thyroid Association: 1st trimester 0.
Finally, immunoassay methods for TSH analysis using nonisotopic, primarily chemiluminescent signals have become available on a variety of high-throughput immunoassay analyzer platforms that employ bar-coding, multiple-analyte random-access, primary tube sampling, auto dilution, STAT testing, and computerized data output Since most thyroid disease is treated on an outpatient basis, point-of-care thyroid tests are unlikely to replace centralized automated thyroid testing.
Liquid chromatography—tandem mass spectrometry testing of thyroid hormones requires equilibrium dialysis or ultrafiltration before analysis. Currently, there is no available methodology to measure TSH, since it is a larger molecule with variable secondary modifications. However, TSH analysis may change when liquid chromatography—tandem mass spectrometry for TSH is made available, by finding smaller fragments of the molecule that can adequately represent TSH activity.
The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health. We thank Chen Fei for help with constructing the figures.
Glycoprotein Hormones: Structure Function and Clinical Implications (Serono Symposia USA)
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Burman , 2 and Offie P. Find articles by Joshua M. Find articles by Danielle Soldin. Timothy M.
Find articles by Timothy M. Kenneth D. Find articles by Kenneth D. Offie P. Find articles by Offie P. Corresponding author. Address correspondence to:, Kenneth D. Copyright , Mary Ann Liebert, Inc. This article has been cited by other articles in PMC.
Abstract Serum thyrotropin TSH is considered the single most sensitive and specific measure of thyroid function in the general population owing to its negative logarithmic association with free triiodothyronine and free thyroxine concentrations. Thyrotropin Synthesis T hyrotropin TSH is a heterodimeric kDa-glycoprotein hormone released from the anteromedial pituitary and is a regulator of thyroid function. Open in a separate window.
TSH Measurements As a single hormone determination, serum TSH immunoassays provide the most sensitive index to reliably detect thyroid function abnormalities 37— Table 1. FT4, free thyroxine; TSH, thyrotropin. TSH sialylation and sulfation Sialylation of the terminal end of the N -linked oligosaccharides is subject to variation that affects biological activity Terminal truncation Human TSH has been shown to be heterogeneous at the amino-terminus of each subunit because of terminal truncation of both unit polypeptide chains.
Endogenous antibodies Some patients may develop autoantibodies against the TSH molecule. Heterophile antibodies Heterophile antibodies are a group of relatively weak, multispecific, polyreactive antibodies with specificity for poorly defined antigens that react with immunoassays derived from two or more species , Human antimouse antibodies Immunometric assays based on monoclonal antibodies of murine origin are more prone to HAMA interference than competitive immunoassays because HAMA are able to form a bridge between the capture and signal antibody reagents and create a signal that is reported as a falsely high value 15 , Disease states associated with apparently higher serum TSH Extremely rare conditions associated with elevated TSH include inherited autosomal recessive forms of partial euthyroid hyperthyrotropinemia or complete congenital hypothyroidism TSH resistance that are associated with biallelic inactivating point mutations of the TSHR gene Central hypothyroidism Idiopathic central hypothyroidism seen in various hypothalamic—pituitary conditions may result from the secretion of biologically inactive TSH.
Resistance to thyroid hormone As previously mentioned, TSH bioactivity is increased in patients with thyroid hormone resistance , Sheehan's syndrome hypothyroidism caused by postpartum panhypopituitarism Sheehan's syndrome is a peripartum condition that follows massive necrosis of the anterior pituitary gland , TSH and Aging TSH immunoactivity and reference intervals in older adults Several epidemiological studies indicate that the normal reference interval for serum TSH increases with age 61 , TSH biological activity and aging Although immunoassay discrepancy may be the underlying reason for the elevated serum TSH, the increase in serum TSH has also been associated with relatively higher concentrations of biologically inactive isoforms of TSH, as described above.
TSH Assessment in Pregnancy Thyroid disorders are relatively frequent in women of childbearing age , ; consequently, TSH measurements are useful in detecting subtle thyroid dysfunction associated with reproductive issues and poor pregnancy outcome. Offie Soldin, died shortly before the final publication of this article.
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Structure–Function Relationships of Glycoprotein Hormones and Their Subunits’ Ancestors
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