Thyroid testing in primary hypothyroidism.

Thyroid hormones regulate essential metabolic processes and development. The hypothalamic-pituitary-thyroid axis regulates hormone production, with thyroid-stimulating hormone (TSH) levels being a key indicator of thyroid function in primary hypothyroidism. This therapeutics letter emphasises a TSH-centred approach to the diagnosis and management of primary hypothyroidism (dysfunction at the level of the thyroid gland) in adults. It discourages routine thyroid function screening in asymptomatic individuals due to a lack of demonstrated benefit and potential harm from overdiagnosis and overtreatment. It outlines appropriate diagnostic strategies, including when to use TSH, free T4 (thyroxine), and free T3 (triiodothyronine) tests, and outlines indications for antibody testing. Special considerations are provided for subclinical hypothyroidism and hypothyroidism during pregnancy.