[Prevalence and clinical characteristics of subclinical hypothyroidism in an opportunistic sample in the population of Castile-León (Spain)].

Objective: To describe the distribution of thyroid-stimulating hormone (TSH) values and to estimate the prevalence of subclinical hypothyroidism in the adult population of Castile and León (Spain).

Method: An observational study was conducted in an opportunistic sample of 45 primary care centers in Castile and León. TSH was determined in people aged ≥35 years that attended a primary care physician and had a blood test for any reason. Confirmatory analysis included free thyroxine and anti-thyroid peroxidase antibody determination.

Results: A total of 3957 analyses were carried out, 63% in women. The mean age was 61.5 years. The median TSH value was 2.3 μIU/mL (2.5 μIU/mL in women and 2.1 μIU/mL in men), with a rising trend with age. TSH values were higher in undiagnosed or untreated subclinical hypothyroidism than in patients under treatment. The lowest levels were found in euthyroidism. The prevalence of subclinical hypothyroidism was 9.2% (95%CI: 8.3-10.2), and hypothyroidism was three times higher in women than in men (12.4% versus 3.7%). Hypothyroidism increased with age, reaching a peak of 16.9% in women aged 45 to 64 years.

Conclusions: The prevalence of subclinical hypothyroidism in our sample was high and in the upper limits of values found in previous studies. Proper diagnosis and treatment are important because of the risk of progression to hypothyroidism and the association with multiple diseases and other risk factors.