TSH — the main test
TSH (thyroid-stimulating hormone) is the first and most important thyroid test. It's made by the pituitary gland in the brain, which raises TSH when it senses the thyroid isn't making enough hormone, and lowers it when there's too much. So a high TSH usually points to an underactive thyroid, and a low TSH to an overactive one.
Because TSH is so sensitive, it's often the only test needed for screening. If it's abnormal, your GP looks further.
Free T4 and free T3
Free T4 (thyroxine) is the main hormone the thyroid produces, and free T3 is the more active form your body converts it into. These are measured to confirm and clarify what TSH is suggesting — for example, a high TSH with a low free T4 confirms hypothyroidism.
Together, TSH and free T4 give a clear picture of whether your thyroid is under-active, over-active, or normal, and how significantly.
Thyroid antibodies
Thyroid antibody tests (such as TPO antibodies) check whether an autoimmune process is behind a thyroid problem — for example, Hashimoto's (a common cause of an underactive thyroid) or Graves' disease (a cause of an overactive thyroid). They help explain the cause and predict how things may progress.
Your GP interprets these together, alongside your symptoms — no single number tells the whole story. If you've had thyroid tests and aren't sure what they mean, a telehealth consult can walk you through your results and any next steps.
Related condition
Thyroid health →References & sources
- 1.Hypothyroidism — healthdirect
- 2.Thyroid gland — healthdirect
- 3.Thyroid gland — Better Health Channel
This content is general information and not a substitute for individual medical advice. Please consult a GP for your personal situation.
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