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What is an Anti-Thyroid Peroxidase (TPO) test?

Thyroid peroxidase or TPO is an enzyme that is produced in the thyroid gland, a small, butterfly-shaped gland just above your collarbone. This enzyme controls the production of thyroid hormones (T3 and T4), which, in turn, play a major role in various metabolic functions in the body.                          

Anti-TPO peroxidase test helps detect antibodies against thyroid peroxidase, which lead to thyroid dysfunction and conditions such as hypothyroidism.

It is the most sensitive test for identifying autoimmune thyroid disorders and helps in detecting various diseases, such as Hashimoto thyroiditis, idiopathic myxoedema and Grave’s disease.

The highest TPO antibodies levels are seen in Hashimoto thyroiditis that is about 90 %, which confirms that it was caused by an autoimmune reaction. In Grave’s disease, about 60-80% of antibodies can be seen.

The test is also known as thyroid peroxidase antibody, thyroperoxidase antibody, anti-TPO or TPO test.

  1. Why is an Anti-TPO test performed?
  2. How do you prepare for an Anti-TPO test?
  3. How is an Anti-TPO test performed?
  4. What do Anti-TPO test results indicate?

This test is usually done in case of the following conditions:

  • Thyroid disease or goitre (abnormal enlargement of the thyroid gland)
  • Hashimoto’s thyroiditis
  • Foetal miscarriage, pre-eclampsia, premature delivery and failure in in-vitro fertilisation
  • Monitoring the severity and progression of hypothyroidism

If a pregnant woman is suspected of a thyroid autoimmune disorder, such as Grave’s disease, Hashimoto’s thyroiditis, other autoimmune disorder or thyroid dysfunction, she must undergo this test at the beginning of her pregnancy as well as at the end, as thyroid antibodies can easily cross the placenta and cause thyroid disorders in the child. Anti-TPO test, in such a case, can help in determining if the baby is at any risk of thyroid dysfunction.

No special preparation is needed for this test.

It can be done at any time of the day, and no fasting is required to be done before this test. However, some medicines can alter the results of this test; hence, it is advisable to inform your doctor if you are on any medications or supplements. Also, it will be preferable if you wear a half-sleeve shirt while going for the test as it would help in an easy collection of the blood sample.

It is a simple blood test wherein a blood sample is collected from a vein in the arm.

Your healthcare provider will first tie an elastic band around your upper arm to make the vein more visible. He/she will then clean the needle injection site with alcohol and withdraw the required amount of blood in a sterile container with the help of an injection. 

After the test, the injection site will be pressed firmly, and a cotton ball or gauze pad will be placed over that area. The collected blood sample will be further sent for examination.

You may feel some tightness due to the elastic band and the needle may cause a quick pinch or sting. Also, some people feel lightheaded after the test or notice a bruise at the needle injection site. though most of these symptoms subside themselves. If you notice any discomfort, make sure to check in with your doctor as soon as possible.

If the test result is positive, it can be indicative of a high risk of developing hypothyroidism in the individuals who:

  • Have subclinical hypothyroidism
  • Are suffering from autoimmune diseases (diabetes type 1)
  • Have a chromosomal disorder (Turner’s syndrome/Down syndrome)
  • Are pregnant or are in the postpartum phase
  • Are on certain medications such as lithium or amiodarone.

The normal value of TPO antibodies is less than 9 international units (IU)/millilitres (mL).

Values more than 9 IU/mL can be suggestive of autoimmune thyroiditis.

Moderate levels can be an indication of non-thyroid autoimmune diseases, such as pernicious anaemia and type I diabetes.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.  

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References

  1. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Antithyroid microsomal antibody
  2. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Antithyroglobulin antibody test
  3. Lab tests online. Thyroid Antibodies. American Association for Clinical Chemistry; Washington, D.C., United States [Internet]
  4. American Thyroid Association. Thyroid Function Tests. Virginia. [internet]
  5. Merck Manual Professional Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; Thyroid Antibodies