Education And Debate

Thyroid function tests—time for a reassessment

BMJ 2000; 320 doi: https://doi.org/10.1136/bmj.320.7245.1332 (Published 13 May 2000) Cite this as: BMJ 2000;320:1332
  1. Denis StJ O'Reilly, consultant clinical biochemist (doreilly@clinmed.gla.ac.uk)
  1. Department of Clinical Biochemistry and Clinic for Thyroid Diseases, Royal Infirmary, Glasgow G4 0SF
  • Accepted 3 November 1999

In 1999, 890 000 measurements of thyroid stimulating hormone were performed by Scottish hospital laboratories—approximately one test for every six of Scotland's 5.1 million people.1 This number does not include tests performed in the non-NHS laboratories or as part of the screening programme for congenital hypothyroidism. Although laboratory statistics are not collected nationally in England and Wales, the market in the United Kingdom (population 59 million) for thyroid stimulating hormone diagnostic tests is currently estimated at 9-10 million each year.

A remarkable downgrading of the clinical aspects of hypothyroidism and hyperthyroidism has paralleled the inexorable increase in the number of thyroid function tests performed over the past 20 years. This has led to chaos in the diagnosis of hypothyroidism. It has been stated that a diagnosis of clinical hypothyroidism can be made on the basis of biochemical measurements alone and that signs and symptoms are unnecessary.2 Other authors protest, and maintain that biochemical tests can be misleading and that the diagnosis can be made on clinical grounds alone.3 In hyperthyroidism, a suppressed thyroid stimulating hormone concentration is currently the cornerstone of biochemical diagnosis. No numerical value has been assigned to the serum concentration of thyroid stimulating hormone below which suppression is considered to occur. This value varies from centre to centre depending on the sensitivity of the local assay. Thus, to many non-specialists the diagnosis of hyperthyroidism is also confusing.

Summary points

There are no data on the relative importance of biochemical thyroid function tests and clinical symptoms and signs in assessing thyroid dysfunction.

Secretion of thyroid stimulating hormone is influenced by many factors other than the negative feedback inhibition by thyroxine or triiodothyronine.

Changes in thyroid stimulating hormone, thyroxine, and triiodothyronine concentrations during systemic illness are poorly understood.

Thyroid function tests cannot be interpreted in patients with systemic …

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