Abnormalities of thyroid hormone metabolism during systemic illness: the low T3 syndrome in different clinical settings
Open accessAbstract
Thyroid hormone abnormalities are common in critically ill patients. For over three decades, a mild form of these abnormalities has been described in patients with several diseases under outpatient care. These alterations in thyroid hormone economy are a part of the nonthyroidal illness and keep an important relationship with prognosis in most cases. The main feature of this syndrome is a fall in free triiodothyronine (T3) levels with normal thyrotropin (TSH). Free thyroxin (T4) and reverse T3 levels vary according to the underlying disease. The importance of recognizing this condition in such patients is evident to physicians practicing in a variety of specialties, especially general medicine, to avoid misdiagnosing the much more common primary thyroid dysfunctions and indicating treatments that are often not beneficial. This review focuses on the most common chronic diseases already known to present with alterations in serum thyroid hormone levels. A short review of the common pathophysiology of the nonthyroidal illness is followed by the clinical and laboratorial presentation in each condition. Finally, a clinical case vignette and a brief summary on the evidence about treatment of the nonthyroidal illness and on the future research topics to be addressed are presented.
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During fasting or relative caloric deprivation, serum T3 is decreased as a homeostatic response to conserve energy and protein.
“During fasting or relative caloric deprivation, for instance, serum T3 is decreased as a homeostatic response to conserve energy and protein.”
From Can Reverse T3 Assay Be Employed to Guide T4 vs. T4/T3 Therapy in Hypothyroidism? (2019) · cites this paper as [13]
Section 4.1 (Caloric Deprivation) reports that serum T3 falls during fasting and caloric deprivation. It says this fall is *believed* to be an adaptive response that saves energy and protein; the citing sentence presents that interpretation as established fact. (LLM, conf=0.86)
Experimental — accuracy not yet measuredFree T4 levels may be transiently increased or normal, while TSH levels may be normal or decreased during fasting or caloric deprivation.
“Free T4 levels may be transiently increased or normal, while TSH levels may be normal or decreased (12, 13).”
From Can Reverse T3 Assay Be Employed to Guide T4 vs. T4/T3 Therapy in Hypothyroidism? (2019) · cites this paper as [13]
A simultaneous increase in rT3 occurs in the first 2 weeks after caloric restriction, followed by normalization.
“A simultaneous increase in rT3 occurs in the first 2 weeks after caloric restriction, followed by normalization.”
From Can Reverse T3 Assay Be Employed to Guide T4 vs. T4/T3 Therapy in Hypothyroidism? (2019) · cites this paper as [13]
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References 91 · Cited by 91
Research works printed but not linked: 1
- [79]Moura Neto A. Parisi M. C. R. Alegre S. M. Pavin E. J. Tambascia M. A. Zantut-Wittmann D. E. Relation of thyroid hormone abnormalities with subclinical inflammatory activity in patients with type 1 and type 2 diabetes mellitus Endocrine 2016 51 1 63 71 10.1007/s12020-015-0651-5 2-s2.0-84953838847 26049370 · DOI
- Authors
- Moura Neto, A., & Zantut-Wittmann, D. E.
- Affiliations
- Division of Endocrinology, Department of Clinical Medicine, Faculty of Medical Sciences, University of Campinas, Campinas, SP, Brazil
- ORCID
- Moura Neto, Arnaldo
- Venue
- International Journal of Endocrinology
- Publisher
- Wiley
- Published
- 2016
- Volume
- 2016
- Pages
- 1-9
- ISSN
- 1687-8337 (ISSN-L)
- 1687-8345
- PMC
- PMC5075641
- OpenAlex
- W2531246579
- Cited by
- 91
- References
- 91
- Citations by year
- 2026: 7 · 2025: 5 · 2024: 11 · 2023: 7 · 2022: 14 · 2021: 19 · 2020: 9 · 2019: 6 · 2018: 7 · 2017: 5
- FWCI
- 0.88
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- International Journal of Endocrinology (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- LA Referencia (Red Federada de Repositorios Institucionales de Publicaciones Científicas) (publishedVersion, other-oa)
- Americanae (AECID Library) (submittedVersion, other-oa)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Funders
- Fundação de Amparo à Pesquisa do Estado de São Paulo (2013/03295-1)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Adrenal Hormones and Disorders
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Hormonal and reproductive studies
- Keywords
- low T3 syndrome, thyroid hormone metabolism, free triiodothyronine, reverse T3, free thyroxine, thyroid-stimulating hormone, chronic disease, critical illness, thyroid hormone replacement
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