Thyroglobulin: what it is, what it tells you and when it’s tested

Thyroglobulin is the protein in which your thyroid builds and stores its hormones. Only the thyroid makes it. That is why its main use is after thyroid cancer: once the thyroid has been removed, thyroglobulin tells the specialist whether any thyroid tissue is left.

When it’s tested

Mostly in check-ups after differentiated thyroid cancer, the most common type. After surgery, and sometimes after radioactive iodine treatment, the specialist measures it over time, together with anti-thyroglobulin antibodies and a neck ultrasound.

It is not used to look for cancer in people with a nodule, or in people who feel well: it rises in almost every thyroid condition, benign ones too, and it cannot tell a harmless nodule from one that is not.

That is why Rosa does not test it. Rosa measures TSH, the first test to see how your thyroid is working.

What it tells you, and what it does not

Once the thyroid has been removed, thyroglobulin should stay very low. If it stays low and stable over time, that is a good sign. If it rises, the specialist does further checks.

In people who still have their thyroid it says little: it rises with a larger thyroid, with nodules, with thyroiditis and with Graves’ disease.

On its own it does not make a diagnosis. The specialist always reads it with the antibodies, the ultrasound and the history of your treatment.

That is why it is read together with other tests:

Normal thyroglobulin levels

There is no normal value that applies to everyone. In people with a thyroid, the lab prints a range that varies with the method, and the value depends a lot on how big the thyroid is.

After thyroid cancer, the range on the report matters little. What matters is the value the specialist expects for you: it depends on how much thyroid was removed, whether you had radioactive iodine, and on your TSH at the time of the test.

That is why check-ups should always be done at the same lab, with the same method: only then can two values be compared.

If your thyroglobulin is high or low

What causes high thyroglobulin

Almost always, cancer is not involved. The most common causes, in people who still have their thyroid:

Thyroglobulin after thyroidectomy

After surgery for differentiated thyroid cancer, thyroglobulin is the simplest check there is: a blood test. Today’s analysers can read even very small values.

If the whole thyroid was removed and you had radioactive iodine, thyroglobulin usually becomes almost or fully undetectable. If only part was removed, or without iodine, some thyroglobulin remains, and that is normal.

What counts is the trend, not a single number. A stable value is reassuring. A rising value leads the specialist to an ultrasound or other tests. Most of these cancers respond well to treatment, and the check-ups are there so you can stay reassured.

What can skew the result

A few things change the value without the disease changing.

When to worry

Talk to your doctor or specialist if:

Frequently asked questions

What are normal thyroglobulin levels? There is no value that is the same for everyone. In people with a thyroid, the range on your report counts, and it varies with the method. After thyroid cancer, what counts is the value your specialist expects for you.

High thyroglobulin: is it cancer? Almost always no. It rises with a goitre, nodules, thyroiditis and Graves’ disease. That is why it is not used to look for cancer in people who have their thyroid.

What should thyroglobulin be after thyroidectomy? It depends on how much thyroid was removed and whether you had radioactive iodine. After complete surgery with iodine, it is usually very low or undetectable. Your specialist tells you the right value for you, and looks mainly at how it changes over time.

Why is it measured with anti-thyroglobulin antibodies? Because the antibodies, if present, can make it look lower than it is. Measured together, they tell your specialist whether the value can be read.

Does Rosa test thyroglobulin? No. Rosa measures TSH, the first test to see how your thyroid is working. Thyroglobulin is ordered by a specialist, usually in check-ups after cancer.

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