Relationship between age and serum thyrotropin among asymptomatic older people in Taiwan

Hypothyroidism is a common disorder in older people, and may be asymptomatic and hard to be diagnosed. The main purpose of this study was to evaluate the distribution of serum thyrotropin (thyroxin-stimulating hormone, TSH) among asymptomatic older people in Taiwan, and to evaluate the relationship between age and serum TSH. In 2007, all subjects participating in the annual elderly health examinations at Taipei Veterans General Hospital were invited for study and were enrolled when they were fully consented. In total, 1716 asymptomatic elderly people (mean age: 73.2+/-4.4 years, 56.3% males) participated in this study after careful exclusion of 38 subjects with past history of thyroid disorders. All participants were divided into two groups: (1) younger old (age 65-79) and (2) older old (age over 80) for further analysis. The mean serum levels of TSH were similar between younger old and older old groups (2.43+/-5.36 microIU/ml for younger old and 2.36+/-3.51 microIU/ml for older old, p=0.444). The overall prevalence of suspected hypothyroidism was 9.2% among asymptomatic older people in Taiwan, which was significantly lower than in Caucasians. The prevalence of suspected hypothyroidism may reach 25.9% if the TSH cutoff was lowered to 2.5 microIU/ml. Further study is needed to determine the normal reference range of serum TSH in older people.