Thyroid dysfunction is common, particularly in the elderly, and has an important impact on morbidity and mortality, especially in this age group.
Aim: We have investigated associations between thyroid function, presence of atrial fibrillation and cognitive function in a large general practice-based study conducted from December 2002-November 2004. Subjects with a previous history of thyroid disease or currently taking thyroxine or anti-thyroid drugs were excluded. We report a preliminary analysis of the data concerning the proportion of subjects with abnormal TSH (measured using a sensitive assay) and fT4 values.
Method: 5784 subjects aged 65 or over had TSH and fT4 measurements performed. The mean age of subjects was 73.5 years; 49.3% male (mean age 73.3), 50.7% female (mean age 73.7). Reference ranges for TSH were 0.4-5.5mU/l and fT4 9-20 pmol/l
Results: Overall, 2.6% of subjects had low serum TSH (0.7% undetectable [<0.1 mU/l], 1.9% detectable but below reference range [>0.1<0.4mU/l]). High serum TSH values were found in 3.3% (2.4% >5.5 <10 mU/l; 0.9% >10mU/l). The mean serum fT4 was 9.5 pmol/l among the 53 with a serum TSH 10 or higher and of these 23 had fT4 values below the reference range. The mean serum fT4 was 13.0 pmol/l among the 136 with a serum TSH in the range >5.5<10; all had fT4 values within the reference range. Among those with detectable TSH, 13 had high fT4 values with a mean of 18.8 pmol/l. Among those with low but detectable TSH mean fT4 was 15.5 pmol/l; 6 of these had fT4 above the reference range but none >22.6 pmol/l.
Conclusion: in this the largest UK based study of community living subjects of 60 years and over we have demonstrated that a high proportion have both hypothyroidism and hyperthyroidism, especially subclinical disease.