Anti-TPO

Anti-TPO are antibodies against thyroid peroxidase, an enzyme the thyroid uses to produce hormones. The test is the main laboratory indicator of autoimmune thyroid disease, particularly Hashimoto’s thyroiditis, and is most often used for elevated TSH, an enlarged thyroid and when planning or during pregnancy.

Who the test is for

• people with elevated TSH or abnormal thyroid hormones when a doctor wants to check for an autoimmune cause;
• people with an enlarged thyroid (goitre) or ultrasound findings suggesting thyroid inflammation;
• women planning pregnancy and pregnant women with high TSH or an increased risk of thyroid disease;
• women with recurrent miscarriage and women undergoing infertility investigation, as assessed by a gynaecologist;
• people with other autoimmune diseases, such as type 1 diabetes, if a doctor considers it necessary.

What anti-TPO antibodies are and what they indicate

Thyroid peroxidase (TPO) is an enzyme in thyroid cells involved in producing T4 and T3 hormones. In autoimmune disease, the immune system mistakenly recognises parts of its own thyroid as foreign and produces antibodies, most commonly anti-TPO. The associated inflammation can gradually impair thyroid function.

Anti-TPO is positive in the great majority of patients with Hashimoto’s thyroiditis (chronic lymphocytic thyroiditis), the most common cause of an underactive thyroid, and in many with Graves’ disease. For Hashimoto’s thyroiditis it is more sensitive than anti-TGantibodies, so it is measured first or alongside them. TSH-receptor antibodies, requested separately by a doctor, are more important for confirming Graves’ disease.

Save with a panel

Test Anti-TPO is also included in this panel.

Complete thyroid panelTSH, T3, T4, fT3, fT4 and 2Price of individual tests: 102.00€92.00€Details ›

Preparation and sample

Anti-TPO is measured in venous blood. Fasting is not required, and blood can be taken at any time; if TSH is also measured, morning is best. If you take levothyroxine, take your tablet after blood sampling that day and do not stop treatment yourself. If you take biotin (e.g. hair and nail supplements), mention it at sampling.

How results are interpreted

The reference value depends on the method and is printed on your report. A doctor interprets results alongside TSH, fT4, anti-TG and thyroid ultrasound.

Positive anti-TPO with high TSH

This combination most often means an underactive thyroid due to Hashimoto’s thyroiditis. With mildly elevated TSH, positive antibodies indicate a greater likelihood of further decline over time, helping a doctor decide on treatment and monitoring intervals.

Positive anti-TPO with normal TSH

Antibodies are also found in some healthy people, more often women and older people. If thyroid function is normal, this is not a disease requiring treatment. However, these people are more likely to develop an underactive thyroid over time, so a doctor usually recommends periodic TSH checks, or earlier checks if symptoms occur.

What anti-TPO does not indicate

Antibody levels do not indicate disease severity or determine treatment. Abnormal thyroid function is treated, for example with hormone replacement when underactive. A negative result does not completely exclude autoimmune disease because some patients have only high anti-TG or no measurable antibodies.

Anti-TPO during pregnancy and when planning pregnancy

Thyroid hormone requirements increase in pregnancy. In women with positive anti-TPO, the thyroid finds it harder to adapt, increasing the likelihood of becoming underactive during pregnancy. A doctor therefore checks TSH more often, particularly in the first half of pregnancy. After childbirth there is also a higher risk of temporary thyroid inflammation (postpartum thyroiditis), which may cause fatigue, palpitations or mood changes.

If TSH is high, a doctor assesses whether hormone replacement is needed, using lower TSH limits in pregnancy than outside pregnancy. In women with normal thyroid function, studies have not shown that hormone replacement solely for positive anti-TPO improves the chance of a live birth, so such results are usually monitored through TSH checks.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Prices for all tests and panels are available in the service price list. When thyroid function is assessed at the same time, the Complete Thyroid Panelis more practical, including anti-TG, TSH, T3, T4, fT3 and fT4 alongside anti-TPO.

Frequently asked questions

Does positive anti-TPO mean I have Hashimoto’s?

Not necessarily. Positive anti-TPO indicates a tendency towards thyroid autoimmunity, but a doctor diagnoses Hashimoto’s thyroiditis using TSH, fT4, symptoms and, if needed, ultrasound. Many people with positive antibodies maintain normal thyroid function for years.

Should high anti-TPO be treated?

The antibodies themselves are not treated. If thyroid function is normal, TSH is monitored; if underactive, a doctor prescribes hormone replacement. Selenium lowered antibody levels in some studies, but this has not been shown to alter the course of disease, so discuss supplements, particularly iodine and selenium, with your doctor first.

Should anti-TPO be repeated?

Generally not. Once a positive result is confirmed, repeating it usually does not change treatment decisions, so TSH is monitored at intervals set by a doctor.

Is positive anti-TPO dangerous in pregnancy?

It is not a reason for fear, but needs closer monitoring. Your gynaecologist should know the result so they can check TSH promptly and start treatment if needed.