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Lookup NU author(s): Dr Salman Razvi
This is the authors' accepted manuscript of a review published in its final definitive form in 2019. For re-use rights please refer to the publishers terms and conditions.
Normalising serum thyroid stimulating hormone (TSH) levels by lifelong treatment with levothyroxine (LT4) remains the primary goal of therapy for patients with hypothyroidism. The reference ranges for TSH are derived from populations with (supposedly) normal thyroid function. But, TSH results are affected by a number of factors including alterations in TSH levels with age, concurrent illnesses, circadian rhythm, inter- and intra-assay differences and some commonly-used medications that interfere with thyroid function or the TSH test. Furthermore, some patients are complex to manage and bringing serum TSH to within its reference range does not always resolve their symptoms of hypothyroidism. In others, changes in TSH within the reference range may provoke symptoms in some sensitive patients, and others may have a personal “set point” forthyroid hormone levels that represents normal function for that individual, but which is outside the population reference range. The introduction of updated LT4 formulations, with better dosing accuracy and stability compared with older versions, should, in theory at least, provide better stability and accuracy of dosing over time. However, the new LT4 formulations were associated with manifold increases in the number of self-reported adverse events. Therefore; patients with hypothyroidism as well as the clinicians managing them need to better understand the utility as well as the limitations of the widely-used TSH measurement. In addition, both pharmaceutical companies and the prescribing clinician need to take greater care when patients are switched from older to newer formulations.
Author(s): Razvi S, Hostalek U
Publication type: Review
Publication status: Published
Journal: Current Medical Research and Opinion
Print publication date: 25/01/2019
Online publication date: 16/01/2019
Acceptance date: 08/01/2019
ISSN (print): 0300-7995
ISSN (electronic): 1473-4877