[Guidelines for the diagnosis and monitoring of thyroid disease].

Background: Thyroid function tests are among the most commonly ordered laboratory tests in the province. In the past, investigations of thyroid disease required more than one test. Sensitive thyroid stimulating hormone (TSH) is the initial test in the diagnosis of hypothyroidism and hyperthyroidism. Free T4 is preferred over total T4 (TT4) measurement to confirm the diagnosis of hypothyroidism or hyperthyroidism. Free T4 (FT4) is the metabolically active form of Total T4 and is a better indicator of thyroid status than Total T4 because it is unaffected by protein binding abnormalities such as pregnancy and oral contraceptives. In some cases of hyperthyroidism the Free T3 may be a more sensitive indicator of hyperthyroidism, whereas the sensitivity of this test in hypothyroidism is very low.