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Variation in the reference range limits of thyroid function tests and association with the prevalence of levothyroxine treatment

Lookup NU author(s): Dr Salman Razvi, Dr Avais Jabbar, Clare Addison



This is the authors' accepted manuscript of an article that has been published in its final definitive form by Oxford University Press, 2023.

For re-use rights please refer to the publisher's terms and conditions.


Many individuals with marginally abnormal thyroid function test (TFT) results may be treated and it is unknown if the limits of the TSH and FT4 reference intervals reported alongside the laboratory results are associated with the prevalence of levothyroxine treatment. We obtained information regarding reported TFT reference intervals from UK National Health Service (NHS) laboratories and evaluated its relationship with the prevalence of levothyroxine treatment for corresponding health areas for 2014. The upper limit of serum TSH was significantly, linearly, independently and negatively associated with prevalent levothyroxine treatment: -0.54% (95% confidence intervals -0.68% to -0.40%). The lower limit of serum FT4 was significantly and independently associated with the prevalence of levothyroxine treatment in a non-linear (J-shaped) manner with an increase being noted from a FT4 level of ยป9.5 pmol/L onwards. We conclude that minor changes in the reference range limits for serum TSH and FT4 are associated with levothyroxine treatment.

Publication metadata

Author(s): Razvi S, Jabbar A, Addison C, Vernazza J, Syed A, Soran H, Leng O

Publication type: Article

Publication status: Published

Journal: European Journal of Endocrinology

Year: 2023

Volume: 188

Issue: 2

Print publication date: 01/02/2023

Online publication date: 08/02/2023

Acceptance date: 30/01/2023

Date deposited: 31/01/2023

ISSN (print): 0804-4643

ISSN (electronic): 1479-683X

Publisher: Oxford University Press


DOI: 10.1093/ejendo/lvad016

ePrints DOI: 10.57711/wbjj-zb62

PubMed id: 36751726


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