What biochemical tests should be prioritized in the evaluation of a patient with suspected thyroid dysfunction?

Prioritized biochemical tests for suspected thyroid dysfunction:

• Measure thyroid-stimulating hormone (TSH) alone initially in adults when secondary thyroid dysfunction (pituitary disease) is not suspected.
• If TSH is above the reference range, measure free thyroxine (FT4) in the same sample.
• If TSH is below the reference range, measure both FT4 and free tri-iodothyronine (FT3) in the same sample.
• For adults when secondary thyroid dysfunction is suspected, and for children and young people, measure both TSH and FT4 initially; if TSH is low, also measure FT3.
• Consider measuring thyroid peroxidase antibodies (TPOAbs) in adults and children with elevated TSH to assess for autoimmune thyroid disease.
• In confirmed thyrotoxicosis, measure TSH receptor antibodies (TRAbs) to confirm Graves' disease; if TRAbs are negative, consider technetium scanning.

These tests form the biochemical basis for diagnosing and differentiating types of thyroid dysfunction and guiding further management.