SUBCLINICAL HYPOTHYROIDISM

SUBCLINICAL HYPOTHYROIDISM
Subclinical hypothyroidism is characterized by normal values for total and free thyroxine (T4) or triiodothyronine (T3) and elevated serum thyrotropin (TSH) levels. There is general agreement that measurement of serum TSH is the most sensitive indicator of thyroid hormone activity in its target tissues (in the absence of pituitary or hypothalamic disease). Since the thyroid affects so many bodily systems, patients often exhibit other, seemingly unrelated symptoms that may in fact be linked to the hypothyroidism. The central issues are whether subclinical thyroid diseases are of sufficient clinical importance to warrant screening or case finding and whether, once these conditions are detected by an abnormal serum thyrotropin value and confirmed by futher testing, therapy is justified. There are few data to guide clinical decisions regarding the treatment of patients with endogenous subclinical hypothyroidism. In some patients the values are normal on retesting weeks or more later, so that intervention should not be considered unless persistently high values are documented. The presence of either a raised thyroid stimulating hormone concentration or thyroid antibodies indicates an increased risk of future hypothyroidism and this is greater when both occur together. Screening for hypothyroidism may be more cost effective than usually presumed and certain subgroups at risk can be identified, but further work is needed to establish the optimum strategy.

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