Thyroid
Anti-TPO
Antibodies against a thyroid protein; may point to an autoimmune disease of the thyroid, such as Hashimoto's disease.
Everything about this testWhat it measures
Thyroid peroxidase (TPO) is an enzyme in the thyroid that is needed to make thyroid hormone. In an autoimmune disease of the thyroid, the immune system makes antibodies against this protein of the body's own: anti-TPO. The test measures how many of these antibodies are in the blood. The antibodies say something about the cause of a thyroid problem, not about how well the thyroid is working at the moment; TSH and free T4 show that.
- Autoimmune disease of the thyroid, especially Hashimoto's disease (chronic thyroid inflammation, the most common cause of an underactive thyroid)
- An increased chance of later developing an underactive thyroid (hypothyroidism), while thyroid function is still normal
High
A raised anti-TPO fits an autoimmune reaction against the thyroid. With an underactive thyroid, Hashimoto's disease is then the most likely cause, but according to the Dutch GP guideline (NHG), anti-TPO does not prove this. Anti-TPO also occurs in people with a normally working thyroid, in temporary thyroid inflammation, in Graves' disease (overactive thyroid) and slightly raised in other autoimmune diseases such as type 1 diabetes or rheumatism. Anyone who has anti-TPO and normal thyroid function has a greater chance of later developing an underactive thyroid; for women, the NHG guideline mentions a chance of 2 to 3 in 100 per year. The level of the value does not say how severe the disease is.
Low
A low or undetectable value is normal. An autoimmune disease of the thyroid is then less likely, but not ruled out. An underactive or overactive thyroid can also occur without anti-TPO, for example after surgery, due to medicines or due to a thyroid nodule.
Preparation
- Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.
If your result is abnormal
With a raised anti-TPO, the GP first assesses TSH and free T4. If thyroid function is normal, treatment is usually not needed and the GP can have TSH measured again if symptoms appear. In pregnancy or when planning a pregnancy, the GP consults the internist (specialist in internal medicine) if thyroid function is abnormal.
Reliability
Anti-TPO is not a test of thyroid function: a thyroid disorder is diagnosed with TSH and free T4. According to the Dutch GP guideline (NHG), anti-TPO cannot distinguish well enough to determine the cause of an underactive thyroid, and the result usually does not change the treatment. The value does help to weigh the chance of a future underactive thyroid.
Limitations
- Healthy people without thyroid symptoms can also have small amounts of anti-TPO.
- Reference values and cut-off values differ per laboratory and measurement method; only compare results from the same laboratory.
- A slightly raised value is not specific and also occurs in other autoimmune diseases.
How common is this
An underactive thyroid affects about 3 to 4 in 100 adults in the Netherlands, more often women and older people. According to the Dutch GP guideline (NHG), in more than 90 in 100 people with an underactive thyroid without a clear other cause, it is Hashimoto's disease. The guideline does not state how many people without symptoms have anti-TPO.
Who is this useful for
Additional information with a previously found abnormal TSH, or with an enlarged thyroid, to see whether an autoimmune disease may be the cause. Also relevant for women who want to become pregnant or are pregnant and have (subclinically) abnormal thyroid function. With symptoms that point to the thyroid, TSH is the first test; anti-TPO on its own says little about how the thyroid is working now.
Downsides and risks
- A positive result with normal thyroid function can cause worry, while no treatment is needed without an abnormal TSH.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results