Anti-thyroglobulin antibodies: what they are, what they tell you and when they’re tested

Anti-thyroglobulin antibodies, often written TgAb or anti-Tg, are antibodies against thyroglobulin: the protein in which your thyroid stores its hormones. They are checked for two different reasons: to see whether there is an autoimmune thyroiditis, and to follow people treated for thyroid cancer.

When they’re tested

Doctors order them in two cases. The first is when they suspect Hashimoto’s thyroiditis, usually together with anti-TPO antibodies, which are more useful.

The second is after thyroid cancer. Here they are always measured together with thyroglobulin, because if they are present they can make it read lower than it is.

They are not needed for people who feel well. On their own, without anti-TPO, they are not linked to thyroid disease. That is why Rosa does not test them. Rosa measures TSH, the first test for the thyroid.

What they tell you, and what they do not

If they are positive together with anti-TPO, there is usually Hashimoto’s thyroiditis. If they are positive on their own, they often mean nothing.

They do not say how your thyroid is working right now: TSH and FT4 tell you that.

After thyroid cancer they tell a different story. Your specialist looks at how they change over time, in the same lab: if they fall, that is a good sign.

That is why they are read together with other tests:

• TSH: It shows how the thyroid is working
• Anti-TPO antibodies: The more useful antibody for Hashimoto’s thyroiditis
• Thyroglobulin: After thyroid cancer they are always measured together
• FT4: It confirms how much hormone the thyroid makes

Normal anti-thyroglobulin antibody levels

Your report usually says whether they are negative or positive, above a limit the lab sets. The limit varies a lot between methods, so always look at the one on your report.

They are common: about one adult in ten has them, more often women, and they become more frequent with age.

If you are followed after thyroid cancer, have them done at the same lab every time: with different methods the numbers cannot be compared.

If your anti-thyroglobulin antibodies are positive or negative

• High anti-thyroglobulin antibodies: With positive anti-TPO, it is usually Hashimoto’s thyroiditis. On their own, they often have no consequences.
• Negative anti-thyroglobulin antibodies: After thyroid cancer, it means thyroglobulin can be read without interference.

High anti-thyroglobulin antibodies: what it means

It depends on who has them and what comes with them. The most common situations:

• Hashimoto’s thyroiditis: Often together with anti-TPO. It is the most common cause of a slow thyroid.
• Graves’ disease: A thyroid that works too hard for an autoimmune reason can also make them positive.
• No disease: With negative anti-TPO and a normal TSH, there is usually nothing to treat.
• After thyroid cancer: About one person in five has them. Your specialist follows them over time, together with thyroglobulin and ultrasound.

After thyroid cancer

After surgery, thyroglobulin helps your specialist check that no thyroid tissue is left. Anti-thyroglobulin antibodies can interfere with that measurement and make it look lower than it is. That is why they are always measured together.

If the antibodies are there, your specialist looks at how they change over time. If they slowly fall, that is usually a good sign. If they rise, your specialist does further checks, such as a neck ultrasound.

What counts is the trend and the same lab, not a single number. Every value is read by the specialist who follows you.

What to know before you read the result

A few details help you read the number well.

• The lab’s method: Limits and numbers vary a lot between labs. To compare two tests, have them at the same place.
• On their own they say little: Without positive anti-TPO and without an abnormal TSH, there is usually no disease.
• After surgery they fall slowly: It can take months or years for them to come down. A slow fall is normal.
• The number is not the severity: A high value does not mean a more serious disease. What counts is how the thyroid works or, after cancer, how the value changes.

When to worry

Talk to your doctor if:

• The antibodies are positive together with anti-TPO, or your TSH is out of range.
• You were treated for thyroid cancer and the antibodies are rising: show it to the specialist who follows you.
• You are pregnant or trying for a baby and have positive thyroid antibodies: tell your gynaecologist.
• You notice a lump or swelling in your neck, or your voice changes for no reason.
• You have trouble breathing or swallowing: call 112 or go to the emergency department.

Frequently asked questions

What are normal anti-thyroglobulin antibody levels? It depends on the lab. Your report gives a limit: below it is negative, above it is positive. The limit on your own report is what counts.

High anti-thyroglobulin antibodies with negative anti-TPO: what does it mean? Often nothing. On their own they are not linked to thyroid disease. If your TSH is normal, usually nothing more is needed. Your doctor decides.

Why are they measured after thyroid cancer? Because they can make thyroglobulin look lower than it is. Measured together, they tell your specialist whether that number can be read, and their trend over time is an extra signal.

Can anti-thyroglobulin antibodies go away? After surgery for thyroid cancer, they often fall slowly, sometimes over a few years. In Hashimoto’s thyroiditis they usually stay, and there is no need to follow them.

Does Rosa test anti-thyroglobulin antibodies? No. Rosa measures TSH, the first test for the thyroid. If your doctor wants anti-thyroglobulin antibodies, they order them separately.

Sources

• Hollowell and colleagues, serum TSH, T4 and thyroid antibodies in the United States population (NHANES III). Journal of Clinical Endocrinology and Metabolism, 2002. PMID 11836274
• Spencer, clinical utility of thyroglobulin antibody measurements for patients with differentiated thyroid cancers. Journal of Clinical Endocrinology and Metabolism, 2011. PMID 21917876
• Caturegli and colleagues, Hashimoto thyroiditis: clinical and diagnostic criteria. Autoimmunity Reviews, 2014. PMID 24434360
• Haugen and colleagues, ATA management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid, 2016. PMID 26462967