Optimal Free Thyroxine Levels for Thyroid Hormone Replacement in Hypothyroidism
Abstract
Objective To determine whether a difference exists in the free thyroxine level required to achieve a normal thyrotropin (thyroid-stimulating hormone or TSH) level between patients with primary hypothyroidism and euthyroid control subjects and compare the free thyroxine levels in patients with primary and secondary hypothyroidism receiving thyroid hormone replacement.Methods We retrospectively assessed TSH and free thyroxine values in 58 patients with primary hypothyroidism and 78 euthyroid control subjects for whom screening thyroid function tests had been performed. From the medical records, we also obtained free thyroxine values for 23 patients with central hypothyroidism receiving stable levothyroxine replacement therapy.Results The mean free thyroxine level was significantly higher in patients with primary hypothyroidism than in euthyroid control subjects (1.36 +/- 0.201 ng/dL versus 1.10 +/- 0.155 ng/dL, respectively; P<or=.0001), whereas the corresponding mean TSH concentrations did not differ significantly (1.60 +/- 1.183 mIU/L versus 1.73 +/- 0.792 mIU/L; P = .46). The mean free thyroxine value was also significantly higher in the patients with central hypothyroidism in comparison with that in the euthyroid control subjects (1.31 +/- 0.278 ng/dL versus 1.10 +/- 0.155 ng/dL, respectively; P<or=.0001), and no significant difference was noted between the patients with primary and central hypothyroidism (1.36 ng/dL versus 1.31 ng/dL; P = .60).Conclusion Patients with hypothyroidism require a higher level of serum free thyroxine to achieve a normal TSH value in comparison with euthyroid control subjects. This finding suggests that patients with central hypothyroidism should be treated to achieve free thyroxine levels in the upper part of the reference range.
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Concentrations of FT4 in the upper part of normal range might represent an appropriate target in most treated CeH patients.
“Several groups [49, 56, 58, 60] reported that concentrations of FT4 in the upper part of normal range might represent an appropriate target in most treated CeH patients (Recommendation 26).”
From 2018 European Thyroid Association (ETA) Guidelines on the Diagnosis and Management of Central Hypothyroidism (2018) · cites this paper as [56]
Patients with hypothyroidism need a higher concentration of serum free thyroxine to achieve a normal TSH concentration compared with euthyroid controls.
“However, patients with hypothyroidism need a higher concentration of serum free thyroxine to achieve a normal TSH concentration compared with euthyroid controls.11”
From Thyroid replacement therapy, thyroid stimulating hormone concentrations, and long term health outcomes in patients with hypothyroidism: longitudinal study (2019) · cites this paper as [11]
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- Authors
- Iverson, J. F., & Mariash, C. N.
- Affiliations
- Abbott Northwestern Hospital (US)
- University of Minnesota (US)
- Corresponding author
- Mariash, Cary N.
- ORCID
- Mariash, Cary N.
- Venue
- Endocrine Practice
- Publisher
- Elsevier BV
- Published
- 2008-07
- Volume
- 14
- Issue
- 5
- Pages
- 550-555
- ISSN
- 1530-891X (ISSN-L)
- OpenAlex
- W2116474364
- Cited by
- 27
- References
- 24
- Citations by year
- 2025: 1 · 2024: 1 · 2023: 1 · 2021: 1 · 2019: 6 · 2018: 2 · 2017: 2 · 2016: 1 · 2015: 2 · 2014: 3 · 2012: 5
- FWCI
- 0.48
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Endocrine Practice (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Medicine › Surgery › Thyroid and Parathyroid Surgery
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Cancer Diagnosis and Treatment
- Keywords
- free thyroxine, thyroid hormone replacement, hypothyroidism, primary hypothyroidism, central hypothyroidism, thyroid-stimulating hormone, levothyroxine, thyroid function tests, reference values
- MeSH terms
- Adult, Female, Humans, Hypothyroidism, Male, Middle Aged, Retrospective Studies, Thyrotropin, Thyroxine, Hormone Replacement Therapy
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