Reference limits of serum TSH and free T4 are significantly influenced by race and age in an urban outpatient medical practice
Abstract
Summary: Objective The suitability of TSH reference limits derived from national databases to outpatient practices has not been established. We aimed to determine whether race and age influence the distribution of TSH and free T4 (fT4). Design A cross‐sectional study of an urban outpatient medical practice. Participants Patients (n = 22 116) without clinical evidence of thyroid disease or use of thyroid‐specific medications. Measurements Comparison of TSH and fT4 distributions in specific racial and age groups including blacks, whites and Hispanics. Results TSH was distributed at higher concentrations, without skew, in whites compared to blacks (median, 1·54 mIU/l vs. 1·18 mIU/l, P < 0·001) and in old (>80 years old) compared to young (20–29 years old) (median, 1·61 mIU/l vs. 1·13 mIU/l, P < 0·001). In all patients, blacks and whites, 3%, 8% and 5%, respectively, of those aged > 80 years were misclassified as having high TSH compared to those aged 20–29 years (P < 0·001). Using TSH limits from national databases resulted in significant misclassification of patients with raised or lowered TSH. Mean fT4 was significantly lower in blacks than whites (17·5 ± 4·38 pmol/l vs. 18·3 ± 3·99 pmol/l, P < 0·001), did not differ between young and old, but decreased progressively (average 7%) as TSH increased to > 4·5 mIU/l. Conclusions Reference limits for TSH differ between races and with age. Use of race‐ and age‐specific reference limits decreases misclassification of patients with lowered or raised TSH in an urban practice. The unique fT4:TSH relationships of blacks and whites may be genetically determined. The implications of the small decrement in fT4 as TSH increases remain to be explored.
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Studies in several populations have shown progressively increasing TSH concentrations with age.
“Studies in several populations (Americans, Scottish, Ashkenazi Jews, Chinese) have shown progressively increasing TSH concentrations with age.”
From Risks of suboptimal and excessive thyroid hormone replacement across ages (2023) · cites this paper as [35]
The 97.5th percentiles of the reference population are considerably higher in the elderly (older than 70 years old) than in younger adults.
“The 97.5th percentiles of the reference population are considerably higher in the elderly (older than 70 years old) than in younger adults [32–35], which is not explained only by higher prevalence of thyroid autoimmunity [36, 37].”
From Risks of suboptimal and excessive thyroid hormone replacement across ages (2023) · cites this paper as [35]
These studies show that the reference range becomes wider as age increases, with lower 2.5 centiles in the older age groups.
“These studies also show that the reference range becomes wider as age increases, with lower 2.5 centiles in the older age groups (Fig. 3).”
From Age-related variation in thyroid function – a narrative review highlighting important implications for research and clinical practice (2023) · cites this paper as [88]
Several large cross-sectional studies in iodine-replete thyroid disease-free populations have reported higher TSH concentrations in older individuals.
“Several large cross-sectional studies in iodine-replete thyroid disease-free populations have reported higher TSH concentrations in older individuals (Fig. 3), [15, 17, 87, 88].”
From Age-related variation in thyroid function – a narrative review highlighting important implications for research and clinical practice (2023) · cites this paper as [88]
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“The 97.5th percentiles of the reference population are considerably higher in the elderly (older than 70 years old) than in younger adults [32–35], which is not explained only by higher prevalence of thyroid autoimmunity [36, 37].”
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Republished: The relationship between serum TSH and free T4 in older people
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- Authors
- Boucai, L., & Surks, M. I.
- Affiliations
- Albert Einstein College of Medicine (US)
- Corresponding author
- Boucai, Laura
- ORCID
- Boucai, Laura
- Venue
- Clinical Endocrinology
- Publisher
- Wiley
- Published
- 2009-03-31
- Volume
- 70
- Issue
- 5
- Pages
- 788-793
- ISSN
- 0300-0664 (ISSN-L)
- 1365-2265
- OpenAlex
- W2003773105
- Cited by
- 141
- References
- 22
- Citations by year
- 2026: 5 · 2025: 6 · 2024: 4 · 2023: 10 · 2022: 5 · 2021: 11 · 2020: 4 · 2019: 10 · 2018: 5 · 2017: 11 · 2016: 5 · 2015: 6 · 2014: 11 · 2013: 23 · 2012: 6
- FWCI
- 4.56
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Clinical Endocrinology (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Medicine › Physiology › Clinical Laboratory Practices and Quality Control
- Health Sciences › Medicine › Surgery › Thyroid and Parathyroid Surgery
- Keywords
- free thyroxine, race, age, racial differences, thyroid function, outpatient practice, urban population, older adults
- MeSH terms
- Adolescent, Adult, Age Factors, Aged, Aged, 80 and over, Black or African American, Child, Child, Preschool, Cross-Sectional Studies, Female, Hispanic or Latino, Humans, Hypothyroidism, Infant, Infant, Newborn, Male, Middle Aged, New York City, Nutrition Surveys, Reference Values, Thyrotropin, Thyroxine, White People, Young Adult
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