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Age-related reference intervals for thyroid function tests are beneficial in adults over 60 years
George Francis Gray Allen1,2, Sarah Blampied2, Kashyap A Patel3
1NIHR Exeter Biomedical Research Centre, University of Exeter Medical School, Exeter, UK.
Annals of Clinical Biochemistry
|February 9, 2026
Summary
Establishing age-specific reference intervals for thyroid stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) is crucial for older adults. Age-related thyroid testing intervals reduce misdiagnosis and unnecessary follow-up in primary care.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Geriatrics
Background:
- Serum thyroid stimulating hormone (TSH) levels naturally rise in healthy older adults.
- Current standard reference intervals for thyroid function tests are not age-specific.
- This can lead to misinterpretation of thyroid test results in the elderly population.
Purpose of the Study:
- To establish age-specific reference intervals for TSH, free thyroxine (FT4), and free triiodothyronine (FT3).
- To evaluate the impact of age-related intervals on primary care thyroid testing outcomes.
- To reduce misdiagnosis and unnecessary testing in older adults.
Main Methods:
- Thyroid hormones (TSH, FT4, FT3) were measured in 1364 healthy adults using Roche Cobas assays.
- Reference intervals were created for all adults, 18-60 years, and over 60 years.
- These intervals were applied to 21,286 primary care thyroid tests to assess their effect.
Main Results:
- In the reference cohort, 23.2% were over 60 years old.
- Using age-related intervals for those over 60 reduced elevated TSH results from 8.2% to 4.4%.
- Subclinical and overt hypothyroidism classifications also decreased significantly with age-specific intervals.
Conclusions:
- A single, all-adult reference interval is inappropriate for the older population.
- Age-related reference intervals for individuals over 60 improve thyroid test interpretation.
- Implementing these intervals can decrease unnecessary repeat testing and patient follow-up.
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