Longitudinal changes in thyroid function and TSH bioactivity in older participants from the Whickham cohort – implications for diagnosis of hypothyroidism

Dr Salman Razvi, Senior Lecturer and Consultant Endocrinologist, Newcastle University and Professor Marian Ludgate, Professor of Molecular Endocrinology, Cardiff University

Dr Salman Razvi and Professor Marian Ludgate 

 

Longitudinal changes in thyroid function and TSH bioactivity in older participants from the Whickham cohort – implications for the diagnosis of hypothyroidism

An underactive thyroid (hypothyroidism) is more prevalent in women and in older people. It is diagnosed when blood thyroid hormone levels (FT4) are low and the pituitary thyroid-stimulating hormone (TSH) is raised. 

Whilst gender, race, smoking, iodine intake and thyroid autoimmunity can all affect TSH and FT4 levels, age is one of the main factors. There is evidence to suggest TSH levels rise in people aged over 70 and that this does not cause them to experience symptoms typical of an underactive thyroid. 

This suggests that mild TSH elevations may be a normal consequence of ageing, rather than reflecting an underactive thyroid.  However, an increasing number of older people are being prescribed levothyroxine (LT4) for minimally raised TSH levels.

Given our ageing population, diagnoses of hypothyroidism are likely to continue to rise. Our study seeks to explore the impact of ageing on thyroid function. It is hoped an improved understanding of hypothyroidism in this age group could lead to age-specific reference ranges being introduced to assess thyroid function, rather than using a TSH normal range obtained from mainly younger people. This could lead to more appropriate management of hypothyroidism in older people. 

To date, we have evaluated thyroid function over time in a group of 42 participants (Whickham cohort) without known thyroid disease. These individuals were tested in 2008/9 and again in 2019. The initial results from this small sample suggest that TSH increases and FT3 levels reduce, whereas FT4 levels do not change. It is important to emphasise that no statistical comparative testing has been performed at this stage. 

Once we have recruited all our participants (400+ in total), we will undertake further tests for TSH bioactivity and thyroid antibodies. We anticipate our final study will be completed in August 2021.