What biochemical tests should be prioritized in the evaluation of a pa

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

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.

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