The thyroid function test is a blood test that can help explain whether the thyroid gland is working as expected. The test request may list TSH, free T4 or other thyroid markers. People sometimes have different panels ordered, depending on whether the doctor is investigating new symptoms or following an existing condition. Bring the prescription to confirm which measurements you need.

The report shows separate results for the thyroid markers that were ordered. Your clinician will consider the pattern across those results alongside your symptoms, medicines and any recent changes in treatment. Tell the healthcare team about the supplements you use, including biotin, since some supplements can affect certain thyroid test results. Ask your doctor whether there are any instructions for your medicines or supplements before the blood sample is collected. If your medicine dose has recently changed, note the date so your clinician can consider it alongside the report.