Thyroid function tests and hypothyroidism

BMJ 2003; 326 doi: https://doi.org/10.1136/bmj.326.7384.295 (Published 08 February 2003) Cite this as: BMJ 2003;326:295

Reducing TSH levels further would be harmful.

DEAR EDITOR - In their recent editorial on thyroid function tests and
hypothyroidism, Toft and Beckett discuss the target TSH (thyroid
stimulating hormone) concentration for patients receiving thyroxine
replacement therapy for primary hypothyroidism.[1] They suggest that
patients with continuing non-specific symptoms (despite a TSH within the
laboratory reference range) are ‘under-­replaced’. They conclude that
simply satisfying the recommendations of the American Thyroid Association
and restoring TSH concentrations to normal is inadequate. They state that
“some patients only achieve a sense of well-being if their TSH is low or
undetectable” and that “most patients feel well only with a low normal TSH

Primary care physicians in the UK provide sole continuing clinical
care for majority of patients (82%) with primary hypothyroidism.[2] Before
considering changing their clinical practice, physicians should know that
almost no empirical evidence exists to support the assertion that
hypothyroid patients feel better with a TSH concentration that is ‘low
normal’, undetectable or suppressed.[1] By comparison, two systematic
reviews with meta-analysis have found that reducing TSH levels with
thyroxine therapy increases the risk of osteoporosis - particularly in
post-menopausal women.[3,4] An issue of considerable clinical importance
as women over the age of 50 years comprise 84% of patients prescribed
thyroxine replacement therapy in primary care.[2] TSH suppression also
increases the risk of atrial fibrillation.[5]

Existing levels of TSH suppression in the community already pose a
threat to women’s health. Many hypothyroid patients are currently over-
replaced with thyroxine in the UK. The proportion of patients with
suppressed levels of TSH is over 20% [2,6] in primary care, whilst
undetectable TSH levels (on ultra-sensitive assay) are 12%.[2] A change in
routine clinical practice which further reduces women’s TSH on thyroxine
replacement therapy is likely to increase both osteoporosis and atrial
fibrillation - without any good evidence that these women will feel any

Dr Mike Crilly


Senior Lecturer in Clinical Epidemiology
& Public Health Medicine.

Aberdeen University Medical School, Department of Public Health, Polwarth Building at Foresterhill, Aberdeen AB25 2ZD


Conflicts of interest: None


[1] Toft AD, Beckett GH. Thyroid function tests and hypothyroidism
Measurement of serum TSH alone may not always reflect thyroid status. BMJ
2003;326:295-296 (8 February)

[2] Crilly,M. Thyroid adherence study. Impact of an educational
booklet on thyroxine adherence inpatients with primary hypothyroidism: a
randomised controlled clinical trial in primary care. [MD Thesis:
submitted University of Manchester UK, 2002]

[3] Faber J, Galloe AM. Changes in bone mass during prolonged
subclinical hyperthyroidism due to L-thyroxine treatment: a meta-analysis.
Eur J Endocrinol 1994;130(4):350-6.

[4] Uzzan B, Campos J, Cucherat M, Nony P, Boissel JP, Perret GY.
Effects on bone mass of long term treatment with thyroid hormones: a meta-
analysis. J Clin Endocrinol Metab 1996;81(12):4278-89.

[5] Sawin CT, Geller A, Wolf PA, Belanger AJ, Baker E, Bacharach P,
et al. Low serum thyrotropin concentrations as a risk factor for atrial
fibrillation in older persons. N Engl J Med 1994;331(19):1249-52.

[6] De Whalley P. Do abnormal thyroid stimulating hormone level
values result in treatment changes? A study of patients on thyroxine in
one general practice. Br J Gen Pract 1995;45(391):93-5

Competing interests:  
None declared

Competing interests: No competing interests

03 March 2003
Mike Crilly
Senior Lecturer in Clinical Epidemiology & Public Health Medicine
Aberdeen University Medical School, AB25 2ZD