Putting thyroid tests into context: results from the Newcastle 85+ study
Professor Simon Pearce, Professor of Endocrinology, Institute of Genetic Medicine, Newcastle upon Tyne, outlines the results of a study he has been involved in that indicates there is no good reason to treat older people with slightly elevated TSH levels provided they are feeling OK.
He explains: Doctors often use information from studies of middle-aged people to make decisions about patients who are over 85, because there are very few studies involving much older people. During 2005 a project was started in Newcastle to find out as much as possible about the health and social circumstances of people over 85. More than 800 people who were born during 1921 agreed to be involved in the study and as well as hundreds of measurements including their body shape, physical state, cognitive tests, dental, lung and cardiac assessments. Their thyroid blood tests results were also recorded. These people were followed up for nine years to find out what happened (when they were either 94 or deceased). The study excluded people already taking levothyroxine, and thyroid function test results were available on 643 people who provided enough health information.
Although there is some evidence that mild thyroid underactivity (with blood TSH in the 5 to 10 mU/l range) is associated with heart disease in younger people, the study showed no survival disadvantage to 85 year olds with high TSH. So this provides evidence that there is no good reason to treat older people with these modestly elevated TSH levels provided they are feeling OK. TSH is therefore different from cholesterol, where there is a lot of reflex prescribing, based on the blood test levels.
In addition, it is well known that when you become poorly for almost any reason (except thyroid over-activity) the blood FT3 levels go down and the ‘complementary’ thyroid hormone metabolite reverse T3 (rT3) goes up. In medical jargon this is sometimes called ‘sick-euthyroid syndrome’. The study confirmed that both lower FT3 and higher rT3 strongly predicted mortality.
- The study also looked at whether thyroid test results could predict who would become disabled in the future. It turns out that for men:
- lower serum TSH predicted progressive disabilities, whereas for women reverse T3 was predictive
interestingly, serum FT4 predicted neither mortality nor disability!
As people continue to live longer, we next need to do a study of 90 year olds.
Full details are available: Pearce et al. Serum thyroid function, mortality and disability in advanced old age: The Newcastle 85+ study. Journal of Clinical Endocrinology & Metabolism 2016 :jc20161935. PMID: 27552542