BMJ  2003;326:1086 (17 May), doi:10.1136/bmj.326.7398.1086-a

Letter

Thyroid function tests and hypothyroidism

Reducing concentrations further would be harmful

EDITOR—In their editorial on thyroid function tests and hypothyroidism, Toft and Beckett discuss the target concentration of thyroid stimulating hormone concentration for patients receiving thyroxine replacement for primary hypothyroidism.¹

They say that patients with continuing non-specific symptoms (despite a thyroid stimulating hormone concentration within the laboratory reference range) are "under-replaced."

They conclude that simply satisfying the recommendations of the American Thyroid Association and restoring thyroid stimulating hormone concentrations to normal is inadequate.

They say that some patients achieve a sense of wellbeing only if their thyroid stimulating hormone is low or undetectable and that most patients feel well only with a low normal thyroid stimulating hormone concentration.¹

Primary care doctors in the United Kingdom provide sole continuing clinical care for most patients (82%) with primary hypothyroidism.² Before considering changing their clinical practice doctors should know that almost no empirical evidence exists to support the assertion that hypothyroid patients feel better with a thyroid stimulating hormone concentration that is "low normal," undetectable, or suppressed.¹ Two systematic reviews with meta-analysis have found that reducing concentrations of thyroid stimulating hormone with thyroxine treatment increases the risk of osteoporosis, particularly in postmenopausal women.^{3 4} This is of considerable clinical importance as women over the age of 50 years constitute 84% of patients prescribed thyroxine replacement in primary care.² Suppression of thyroid stimulating hormone also increases the risk of atrial fibrillation.⁵

Many hypothyroid patients are currently over-replaced with thyroxine in the United Kingdom. The proportion of patients with suppressed concentrations of thyroid stimulating hormone is over 20% in primary care, while undetectable thyroid stimulating hormone concentrations (on ultra-sensitive assay) are 12%.² A change in routine clinical practice that further reduces concentrations of thyroid stimulating hormone in women receiving thyroxine replacement is likely to increase both osteoporosis and atrial fibrillation, without any good evidence that these women will feel any better.

Aberdeen University Medical School, Aberdeen AB25 2ZD mike.crilly{at}abdn.ac.uk

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Competing interests: None declared.

References

1. Toft AD, Beckett GH. Thyroid function tests and hypothyroidism. BMJ 2003;326: 295-6. (8 February.)[Free Full Text]
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, United Kingdom, 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: 350-6.[Abstract]
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: 4278-89.[Abstract]
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: 1249-52.[Abstract/Free Full Text]

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