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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.
Older adults with normal thyroid function or subclinical thyroid dysfunction show notable long-term stability of their thyroid hormone levels. This suggests that it is safe for GPs not to routinely retest older adults unless they have risk factors or develop clinical symptoms of overt thyroid dysfunction.
Over five years, about 0.2% older adults with normal thyroid function will develop overt hypothyroidism and about 3.5% will develop subclinical hypothyroidism. Amongst those with subclinical hypothyroidism, about 2% will develop overt hypothyroidism.
The NIHR funded this study as there is a lack of consensus on the relevance of subclinical thyroid dysfunction and the need for repeat testing.
This could both reduce the burden of unnecessary repeat testing on patients and save the NHS resources.
Why was this study needed?
Thyroid dysfunction is common in older adults. It can be caused by a range of health problems and certain medications. Around 5-6% of UK adults have subclinical hypothyroidism, where blood tests indicate possible underactivity, but the person has no clinical symptoms. Around 1% have subclinical hyperthyroidism: possible overactivity but no symptoms.
There is substantial variation in how people with subclinical thyroid dysfunction are monitored. The study authors estimate that thyroid function tests are requested for around 30% of older adults without overt signs of thyroid disease in UK general practices every year. The total annual cost of thyroid function testing in the UK is £30 million.
This study aimed to establish the stability of thyroid function in older people with subclinical disease, and determine whether repeat testing is necessary.
What did this study do?
This study, BETS 2, followed up participants from the BETS 1 study. BETS 1 provided thyroid screening of 5,881 adults aged 65 years or older across 20 general practices in the UK. The current study involved 2,936 adults whose initial tests were either normal or indicated subclinical thyroid dysfunction: 94% of these were normal at baseline, 5% subclinically hypothyroid, and 1% subclinically hyperthyroid. Those who received active therapy within the BETS 1 study had been excluded.
Participants were invited for repeat thyroid function tests approximately five years after BETS 1 to look for a change in thyroid status. Thyroid function was determined from a single test on both occasions.
What did it find?
- Of participants with normal thyroid function at baseline, 96% continued to have normal thyroid function five years later. Additionally: 3.5% developed subclinical hypothyroidism at five years, 0.2% developed overt hypothyroidism, 0.5% developed subclinical hyperthyroidism, and 0.3% developed overt hyperthyroidism.
- Of participants with subclinical hypothyroidism at baseline: 58% stayed the same at five years, 40% reverted to normal, and 2% developed overt hypothyroidism.
- Of 25 participants with subclinical hyperthyroidism at baseline: 64% stayed the same at five years, 32% reverted to normal, and 4% developed overt hyperthyroidism.
- The risk of developing overt hypothyroidism was greater for people with higher thyroid stimulating hormone or lower FT4 at baseline, later diagnosis of atrial fibrillation or renal disease, or who started taking the drug amiodarone.
What does current guidance say on this issue?
NICE guidelines on the assessment and management of thyroid disease are in development and are expected to be published in November 2019.
A detailed 2006 guideline from the British Thyroid Foundation outlines the indications for thyroid function testing and subsequent management. This guideline does recommend repeat testing and ongoing monitoring in people who may have subclinical thyroid dysfunction but recommends against routine testing of people acutely admitted to hospital unless there are specific clinical indications.
What are the implications?
This is the largest study to investigate the natural progression of thyroid function in the general population of older adults in the UK.
The findings offer reassurance to GPs and hospital clinicians that older adults with normal thyroid function or subclinical dysfunction are unlikely to develop overt thyroid dysfunction over the following five years.
It suggests that routine retesting in these adults could be safely reduced, with clinical assessment of thyroid symptoms and risk factors used to guide retesting. Avoiding unnecessary repeat testing will reduce the burden of testing for patients, and save NHS resources.
Citation and Funding
Roberts L, McCahon D, Johnson O et al. Stability of thyroid function in older adults: the Birmingham Elderly Thyroid Study. Br J Gen Pract. 2018;68(675):e718-26.
This study was funded by the National Institute for Health Research School for Primary Care Research (SPCR).
Bibliography
British Thyroid Foundation. Thyroid function tests. Harrogate: British Thyroid Foundation; 2006.
UK NSC. The UK NSC recommendation on thyroid disease screening in adults. London: UK National Screening Committee; 2018.
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