[Subclinical hypothyroidism--a condition that must be treated?]

Subclinical hypothyroidism, defined as serum thyrotropin above the upper reference limit with normal estimates of free thyroxin in serum, has a prevalence in Denmark of 2%. Several investigations have shown that patients with subclinical hypothyroidism have subtle symptoms and signs of mild thyroid failure. Whether these patients require treatment or not is a controversial issue due to a lack of convincing evidence regarding the beneficial effects of hormone replacement, especially in patients with serum TSH <10 mU/L. However, when it comes to treatment of pregnant or fertile women planning pregnancy, no doubt prevails, as normal thyroid function is important for optimal pregnancy outcome.