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Thyroid peroxidase


The thyroid is a small, butterfly-shaped gland on the neck, in front of the tracheae. It primarily produces thyroid hormones, i.e. thyroxine (T4) and triiodothyronine (T3), to regulate the speed of energy consumption. Microsomal thyroid peroxidase (TPO) helps to transform T4 to T3 and vice versa, from T3 to T4, according to the needs of the body. When a person’s own immune system mistakes the thyroid gland or its proteins as foreign, you develop thyroid autoimmune disease, and your blood has auto-antibodies against thyroid peroxidase (TPOAb). The antibodies affect TPO's role in balancing thyroid hormones, and the body develops conditions where the level of thyroid hormones is too high or too low, leading to thyroiditis (inflammation of the thyroid gland), tissue damages and disturbance of thyroid function. TPO antibodies are more common in women than in men. If a pregnant mother has TPO antibodies, it increases the risk of giving birth to a child with hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid).

When should TPOAb be measured?

Hypothyroidism (underactive thyroid) can cause symptoms

  • Weight gain
  • Fatigue
  • Feeling of pressure on the neck (enlarged thyroid gland)
  • Dry skin
  • Hair loss
  • Intolerance to cold
  • Constipation

Hyperthyroidism (overactive thyroid) can cause symptoms

  • Sweating
  • Fast pulse
  • Anxiety
  • Tremor
  • Fatigue
  • Sleep problems
  • Sudden weight loss
  • Bulging eyes
What does a TPOAb test measure?

The test shows if there are thyroid antibodies in the blood in case of detected or suspected disorder of thyroid function. Antibody testing is requested primarily to help to diagnose autoimmune thyroid disease and to distinguish it from other inflammations of the thyroid gland and other forms of thyroid diseases.

Normally, the result is:

< 6 kU/l

Read more about defining reference values.

Please contact your physician or other healthcare professional if you suspect an illness or need help interpreting the results.

Typically, the higher the antibody levels, the more likely it is that you have an autoimmune thyroid disease. Significantly increased levels often indicate autoimmune thyroid diseases (Hashimoto disease and Graves disease), which cause hypothyroidism. Thyroid antibodies are also found in other autoimmune diseases, such as childhood diabetes (type I diabetes), pernicious anaemia, rheumatoid arthritis and systemic lupus erythematosus (SLE).

The test has no lower limit. Normally, TPO antibodies occur in approximately 20% of women and 8% of men.

Triiodothyronine, free, indicates hyperthyroidism (2775 S-T3-V) Thyroxine, free, index of thyroid function (2836 S-T4-V) TSH indicates thyroid disease (2832 TSH)

SYNLAB test list: Thyroid peroxidase, antibodies (4028 S -TPOAb) https://www2.synlab.fi/laboratoriokasikirja/tutkimuskuvaukset/tyreoideaperoksidaasi/

Terveyskirjasto health library: Autoimmune diseases https://www.terveyskirjasto.fi/terveyskirjasto/tk.koti?p_artikkeli=dlk00010&p_hakusana=kilpirauhasen%20vasta-aineet

Lab Test online: Thyroid Antibodies https://labtestsonline.org.uk/tests/thyroid-antibodies

Schalin-Jäntti C. Krooninen autoimmuunityreoidiitti (Chronic autoimmune thyroiditis). Terveysportti, 28 January 2019. https://www.terveysportti.fi/apps/ltk/article/ykt00587/search/tpo


Fasting is not required

This examination does not require fasting