Thyroglobulin (Tg)
Thyroid protein, mainly used as a follow-up marker after thyroid cancer
Also known as
Definition
Thyroglobulin is a protein made by the thyroid gland and released into the blood in small amounts. Cells of papillary and follicular thyroid cancer also make it. That is why the test is mainly used as a tumor marker in follow-up after treatment for these cancers. Because many thyroid conditions change the level, thyroglobulin is not used to diagnose cancer. Not to be confused with thyroglobulin antibodies.
| Parameter | Value |
|---|---|
| Unit | ng/mL (µg/L) |
| Reference Range | No uniform range: the limits depend on the lab's test method. After treatment that has removed all thyroid tissue, a very low or undetectable level is expected. The reference range on your own report is what counts. Discuss your result with your doctor. |
Agree on your personal target range with your doctor.
1 ng/mL equals 1 µg/L. Results from different test methods are not directly comparable.
↓ What a low value means
After treatment for thyroid cancer, a very low or undetectable level may indicate that the thyroid tissue, including cancer tissue, has been removed; further checks are still needed over time. Outside cancer follow-up, a low level may be related to an underactive thyroid. Thyroglobulin antibodies in the blood can make the measured level appear falsely low. Discuss your result with your doctor.
↑ What a high value means
A raised level may be related to an overactive thyroid, thyroid inflammation (temporarily) or papillary or follicular thyroid cancer. After cancer treatment, a level that stays high or rises again may indicate that thyroid or cancer tissue is still present or that the cancer has come back. That is why the trend over several measurements matters most. Interpretation belongs with your doctor.
When to test
Thyroglobulin is measured before treatment for thyroid cancer as a baseline, about four to six weeks after treatment and then regularly during follow-up, and less often in other thyroid conditions. Usually no preparation is needed. Tell your provider which vitamins and supplements you take, because some can interfere with the test.
Frequently asked questions
What is the difference between thyroglobulin and thyroglobulin antibodies? +
Thyroglobulin is a protein of the thyroid. Thyroglobulin antibodies are proteins of the immune system directed against it. They can occur in autoimmune thyroid disease and can distort the thyroglobulin measurement. That is why both are often measured together.
Why should follow-up tests be done at the same lab? +
Labs measure thyroglobulin with different methods, and the method affects the result. If tests are done the same way and usually at the same lab, values can be compared more reliably over time.
Can biotin affect the result? +
Yes, depending on the test method. In one study, taking biotin led to falsely lower thyroglobulin levels on one of the measuring systems examined. So tell your provider which supplements you take and follow your practice's instructions.
Does a raised thyroglobulin level indicate cancer? +
No, not on its own. An overactive or inflamed thyroid can also raise the level. The test is mainly used to follow the course of a cancer that is already known.
Thyroglobulin (Tg)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.