Blood draw
Thyroglobulin
Thyroglobulin (Tg); a protein produced by thyroid tissue.
€ 55,00
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Thyroid · Blood
Thyroglobulin
A protein made only by the thyroid; the value depends on how much thyroid tissue there is and whether it is damaged.
At a glance
- Measured in blood
- In 2 test panels
- No special preparation
Explanation
Thyroglobulin: what is measured?
Thyroglobulin (Tg) is a protein made only in the thyroid; the thyroid uses it to build thyroid hormone. A small part normally enters the blood. The more thyroid tissue there is and the more strongly it is stimulated or damaged, the higher the value. The measurement says nothing about how well the thyroid works; TSH and free T4 show that. Antibodies against thyroglobulin (anti-Tg), which occur in many thyroid disorders, disturb the measurement.
What can it detect?
- The amount and activity of thyroid tissue, for example with an enlarged thyroid (goiter) or nodules
- Damage to or inflammation of the thyroid (thyroiditis)
- In an overactive thyroid, the distinction between the thyroid's own overproduction and taking too much thyroid hormone, in which thyroglobulin is actually low
- Rarely: monitoring after treatment of a thyroid tumor, in which the course over several measurements is followed
Result
What does the result mean?
Thyroglobulin too high
A raised value usually has a benign cause: an enlarged thyroid (goiter), one or more nodules, Graves' disease, inflammation of the thyroid or a recent needle biopsy or operation on the thyroid. Iodine deficiency and pregnancy can also raise the value. A raised value says nothing about how well the thyroid works. Rarely: after treatment of a thyroid tumor, a rising value can point to thyroid tissue that has come back; this is assessed from the course over several measurements and not from one single value.
Thyroglobulin too low
In people with a normal thyroid, a low value is usually normal. After removal or ablation of the thyroid, the value should be low or unmeasurable. With an overactive thyroid, a low value fits taking too much thyroid hormone, for example through tablets or slimming products, rather than the thyroid's own overproduction. Antibodies against thyroglobulin can make the result falsely low.
After an abnormal result
With an abnormal value, the GP looks at TSH, free T4 and anti-Tg. If these are normal and there are no symptoms or swellings in the neck, no further tests usually follow. With an enlarged thyroid or a palpable nodule, a physical examination follows and, if needed, an ultrasound and referral to an internist (specialist in internal medicine).
Reliability
How reliable is the test?
Thyroglobulin says nothing about thyroid function; according to the Dutch GP guideline (NHG) on thyroid disorders, that is determined with TSH and free T4. The value is raised in many benign thyroid disorders, which makes a single raised value not very specific. Antibodies against thyroglobulin make the measurement unreliable, usually falsely low; without anti-Tg alongside it, a result cannot be interpreted properly. According to the Dutch Society for Clinical Chemistry (NVKC), there are no general reference values, because the result depends strongly on the measurement method; the result means the most when the course is followed in the same laboratory.
What can affect the result?
- Antibodies against thyroglobulin (anti-Tg) disturb the measurement; always measure anti-Tg as well.
- Measurement methods differ greatly; only compare results from the same laboratory.
- After a needle biopsy, operation or inflammation of the thyroid, the value is temporarily higher; iodine deficiency, pregnancy and a high TSH also raise the value.
- Biotin supplements can disturb some measurement methods; stop biotin at least two days before the sample collection.
Who it is for
Who is the test useful for?
Useful for
With symptoms that fit a thyroid disorder, TSH and free T4 show how the thyroid is working; thyroglobulin says nothing about that. The result means the most in people whose thyroid has been removed or treated, if the course is followed over several measurements in the same laboratory and anti-Tg is measured as well. In people without thyroid symptoms, a single value says little.
How common is it?
An underactive thyroid affects about 3 to 4 in 100 adults in the Netherlands and an overactive thyroid about 1 in 100, both more often women. Nodules in the thyroid are common, especially at older ages, and are almost always benign. How often a raised thyroglobulin occurs in people without symptoms is not well known.
NIVEL primary care registrations and the NHG guideline on thyroid disorders
Drawbacks and risks
- A raised thyroglobulin usually has a benign cause, but can cause unnecessary worry and unnecessary further tests.
- If anti-Tg is present, a normal or low value can give false reassurance.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and resultsMore explanations
Other tests: Thyroid
- Anti-Tg
- Anti-TPO
- Free T3
- Free T4
- Reverse T3
- T3 (total)
- Thyroxine-binding globulin
- Total T4
- TSH
- TSH receptor antibodies (TRAb)