Prevalence study of thyroid dysfunction in the elderly of Taiwan

The present study was aimed at investigating the prevalence of thyroid dysfunction in the elderly, aged 65 years or older, in a community of southern Taiwan. By using the records of the local household registry, a sampling frame for the elderly population was constructed, and a sample of 1,400 subjects was drawn by simple random sampling. After the exclusion of nonresponse subjects, 917 subjects aged between 65 and 88 years (mean 71.9) were included in our survey. The serum thyrotropin levels of these participants were measured by monoclonal antibodies TSH immunoradiometric assays. A normal range, 0.45-4.65 microU/ml, was determined from the middle 95% of the TSH distribution of 140 'disease-free' subjects. By reference to the normal range, 23 (2.51%) participants had high (> 4.65 microU/ml), and 41 (4.47%) had low (< 0.46 microU/ml) TSH levels. The overall prevalence of thyroid dysfunction in the sample was 6.98%. Of the 23 participants with high TSH levels, 8 (34.8%) had low free T4 values (< 1.21 ng/dl), so-called overt hypothyroidism, and of the 41 participants with low TSH levels, only 1 (2.4%) had high T3 values, so-called T3 thyrotoxicosis. Antithyroid antibodies were found in 56.5% of those with high TSH levels but only 12.2% of those with low TSH levels (odds ratio = 8.53, 95% confidence limits = 2.55-28.50, p < 0.001). This result indicates that autoimmune disease is still the major cause of hypothyroidism in aged people. However, the prevalence of subclinical hyperthyroidism is higher than that of subclinical hypothyroidism and it might relate to nonautoimmune factors.