Thyroglobulin test
Quick answer: A thyroglobulin test measures a protein made by thyroid cells. It is mainly used after treatment for thyroid cancer to check whether any thyroid tissue or cancer has come back.
- SampleBlood
- TakesAbout 5 minutes
- Before the testNo special preparation is usually needed.
How the test is done
- 1The test is usually timed by your thyroid cancer team
- 2A vein in your arm is cleaned
- 3Blood is drawn, often with a thyroglobulin antibody test from the same sample
- 4Results are compared with your earlier levels over time
What your results can mean
Reading your report
It is usually read with a thyroglobulin antibody test, as antibodies can affect the result; discuss it with your doctor.
If the result is outside the usual range
After thyroid cancer treatment, a rising or detectable level can suggest remaining thyroid tissue or a return of cancer. In people who still have their thyroid, raised levels can be seen with goitre, thyroid nodules or an overactive thyroid.
Who usually has this test
People who have been treated for differentiated thyroid cancer and are having regular follow-up.
Risks and aftercare
Mild tenderness at the needle site is possible; your cancer team will tell you when the next check is due.
Names and options
Also called: Tg test, serum thyroglobulin
Listed by the hospital as
- THYROGLOBULIN, SERUM
Questions about this test
Why is thyroglobulin checked after thyroid cancer?
After the thyroid is removed and treated, there should be very little thyroglobulin in the blood. A rising level over time can be an early sign that cancer has come back.
Why is a thyroglobulin antibody test done at the same time?
Antibodies against thyroglobulin can interfere with the test and make the result falsely low. Checking for them tells your doctor whether the result can be trusted.
Is thyroglobulin used to diagnose thyroid cancer?
No. Thyroglobulin can be raised in many non-cancerous thyroid conditions, so it is not used to diagnose cancer. Its main use is follow-up after treatment.
Related tests
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.