title: Thyroid function in critically ill patients.
abstract: Patients in the intensive care unit (ICU) typically present with decreased concentrations of plasma tri-iodothyronine, low thyroxine, and normal range or slightly decreased concentration of thyroid-stimulating hormone. This ensemble of changes is collectively known as non-thyroidal illness syndrome (NTIS). The extent of NTIS is associated with prognosis, but no proof exists for causality of this association. Initially, NTIS is a consequence of the acute phase response to systemic illness and macronutrient restriction, which might be beneficial. Pathogenesis of NTIS in long-term critical illness is more complex and includes suppression of hypothalamic thyrotropin-releasing hormone, accounting for persistently reduced secretion of thyroid-stimulating hormone despite low plasma thyroid hormone. In some cases distinguishing between NTIS and severe hypothyroidism, which is a rare primary cause for admission to the ICU, can be difficult. Infusion of hypothalamic-releasing factors can reactivate the thyroid axis in patients with NTIS, inducing an anabolic response. Whether this approach has a clinical benefit in terms of outcome is unknown. In this Series paper, we discuss diagnostic aspects, pathogenesis, and implications of NTIS as well as its distinction from severe, primary thyroid disorders in patients in the ICU.
authors.affiliation: Department of Endocrinology and Metabolism, Academic Medical Centre, University of Amsterdam, AZ, Amsterdam, Netherlands.
authors.forename: Eric
authors.initials: E
authors.lastname: Fliers
authors.affiliation: Division of Endocrinology and Metabolism, Rush University Medical Center, Chicago, IL, USA.
authors.forename: Antonio C
authors.initials: AC
authors.lastname: Bianco
authors.affiliation: Laboratory of Intensive Care Medicine, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium.
authors.forename: Lies
authors.initials: L
authors.lastname: Langouche
authors.affiliation: Department of Endocrinology and Metabolism, Academic Medical Centre, University of Amsterdam, AZ, Amsterdam, Netherlands. Electronic address: a.boelen@amc.uva.nl.
authors.forename: Anita
authors.initials: A
authors.lastname: Boelen
mesh_terms: D016638:Critical Illness; D005067:Euthyroid Sick Syndromes / Q000378:metabolism*; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*; D013974:Thyroxine / Q000378:metabolism*
chemical_list: D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D013974:Thyroxine