Prevalence of subclinical hypothyroidism in a population living in the Milan metropolitan area

Subclinical hypothyroidism is a condition characterized by increased levels of thyroid-stimulating hormone (TSH) associated with normal levels of free triiodothyronine (FT3) and free thyroxine (FT4). The exact prevalence of t his condition in Italy is not known. The aim of this study was to assess th e presence of subclinical hypothyroidism in 1001 subjects living in the Mil an area (age 17-89) and apparently free from thyroid pathology. This sample which had;applied to a large laboratory centre (Centro Diagnostico Italian o, Milano) for a routine check-up was seen from April to July 1996. A serum TSH assay was performed using a highly sensitive immunoenzymatic method, w hile an FT3 and FT4 assay was performed by means of a radioimmunologic meth od using commercial kits. The prevalence of subclinical hypothyroidism in t he total population proved to be 4.7% (95% CI-Confidence Interval: 3.4-6.0) . Sex stratification showed a prevalence of 6.1% in females and 3.4% in mal es. Prevalence in patients up to 65 was 4.2%. This value increased up to 8. 0% in subjects over 65. By combining these variables, in females >65 preval ence increased to 11.3%. Overall, symptoms typical of overt hypothyroidism were found in 58.3% of patients suffering from subclinical hypothyroidism a nd in 39.9% of healthy subjects (p<0.02). The results of this study show th at there is a significant presence (about 5%) of subclinical hypothyroidism in this population and that its frequency is more than doubled in women ov er 65. Early treatment might reduce the progression to overt hypothyroidism . The benefits of such a procedure were recently suggested by a decision ma king modelling approach applied to the Italian environment.