Thyroid Peroxidase Antibodies

What are Thyroid Peroxidase Antibodies (TPO)?

Thyroid peroxidase is an enzyme normally found in the thyroid gland that’s used to make thyroid hormones (thyroxine and triiodothyronine)^[1]. Sometimes, the body produces antibodies against thyroid peroxidase called thyroid peroxidase antibodies (TPO).

Antibodies circulate in the blood in response to foreign proteins called antigens and help to protect the body against pathogens like bacteria and viruses. If thyroid antibodies develop, the immune system mistakenly attacks the thyroid cells, causing inflammation and disrupted thyroid function.

High levels of TPO antibodies suggest the presence of thyroid disease caused by an autoimmune condition, such as Hashimoto’s thyroiditis.

What are Normal Thyroid Peroxidase Antibody Levels?

The normal reference range for thyroid peroxidase antibodies is 0 to 34 IU/mL^[2]. A value above this could suggest thyroid dysfunction and may require further tests to determine the underlying cause.

Data collected from Forth customers shows that the average TPO antibody level is 44.6 IU/mL and that all age groups have an increased level except for the 18 to 29-year age bracket. Research has shown that TPO antibodies are more likely to occur in women and increase with age^[3]. Thyroid dysfunction, including an underactive thyroid (hypothyroidism), is common in postmenopausal and elderly women^[4].

Hashimoto’s thyroiditis, an autoimmune condition characterised by thyroid autoantibodies and thyroid peroxidase antibodies is the most common cause of an underactive thyroid. Hypothyroidism is most common in women aged 30 to 50^[5].

Although the graph below shows the average TPO levels for both sexes, it is clear that the values follow the patterns found in the research with TPO levels highest in those aged 30 – 39, 50 – 59, and over 60.

What Causes High Thyroid Peroxidase Antibody Levels?

Thyroid disease causes high TPO antibodies in the blood, specifically if an autoimmune condition causes it.

The two main types of thyroid disease are hyper- and hypothyroidism but they each have various causes. The thyroid gland is a small butterfly-shaped gland located in the neck that’s responsible for producing thyroid hormones. The hormones have critical roles in regulating the speed of your metabolism.

In some people, antibodies develop which mistakenly attack the thyroid cells causing dysfunction.

Causes

The main causes of raised TPO in the blood are the autoimmune conditions Hashimoto’s thyroiditis and Graves’ disease.

Hashimoto’s thyroiditis

Hashimoto’s disease is a chronic lifelong autoimmune condition affecting the thyroid gland. It is the most common cause of hypothyroidism in the developed world. Hashimoto’s disease is caused by the body developing anti-thyroid antibodies that attack the thyroid tissue, causing fibrosis and resulting in high thyroid stimulating hormone (TSH) levels, low thyroxine (T4), and high TPO antibody levels.

Women are most commonly affected by Hashimoto’s disease and it can cause an increase in other biomarkers, including:

• Creatine kinase

• Prolactin

• Total cholesterol

• Low-density lipoprotein

• Triglycerides^[6]

Graves’ disease

Graves’ disease is also an autoimmune disorder that causes an overactive thyroid or hyperthyroidism. That means the thyroid gland produces too much of the thyroid hormones, causing the metabolism to speed up.

According to the NHS, around 4 out of 5 people diagnosed with hyperthyroidism have Graves’ disease. The exact cause isn’t known but it affects mostly middle-aged women and runs in families^[7].

Graves’ disease is the most common cause of hyperthyroidism and is more common in women than men^[8]. Raised TPO levels aren’t always present in people with Graves’ disease, so other thyroid biomarkers will need to be analysed. However, approximately 70% of Graves’ disease patients will have raised TPO^[9].

Symptoms

Should I be worried about cancer if my TPO antibody levels are high?

Not necessarily. High TPO antibodies occur in around 10 to 20% of thyroid cancer patients compared to 65 to 75% of Hashimoto’s disease patients. However, they can also be raised in people whose thyroid gland is functioning normally^[12].

Some research has shown that increased TPO levels could be a strong predictor for thyroid cancer^[13]. However, the research isn’t conclusive because other studies have found that high TPO antibodies could be protective against thyroid cancer in people with hypothyroidism^[14].

The main symptoms of thyroid cancer are:

• A hard, non-painful lump at the front of your neck that slowly gets bigger

• Sore throat

• Hoarse voice

• Trouble swallowing or breathing

• Feeling like something is pressing against your neck^[15]

Managing Your Thyroid Peroxidase Antibody Levels

Scientists are not completely sure what causes the immune system to attack the thyroid cells, but it is likely to be a combination of genetics and environmental factors^[16].

If you are diagnosed with an autoimmune thyroid disorder, you may be given treatment by your doctor, such as levothyroxine to increase your thyroxine levels, but there are things you can do to support your thyroid function, such as:

• Eating a healthy, balanced, and varied diet

• Avoiding iodine and iodine supplements because this can make the condition worse

• Getting regular exercise to help manage some of the symptoms associated with an over or underactive thyroid

Selenium supplements

Selenium is a naturally occurring mineral that’s an essential part of the human diet. That means you must get it from the food you eat because the body cannot make it. Some evidence suggests that selenium supplementation could help with the management of Hashimoto’s thyroiditis. A review published in 2023 found that 6 months of supplementation of selenium lowered TPO antibody levels in people with Hashimoto’s^[17].

Vitamin D

People with Hashimoto’s disease are more likely to be deficient in Vitamin D and calcium^[18]. Vitamin D supplementation could be useful for autoimmune hypothyroidism because it can improve immunological markers and clinical outcomes^[19]. A 2016 study demonstrated that vitamin D supplementation had a beneficial effect on TPO levels in people with autoimmune thyroid disorders^[20].

How to Test Your Thyroid Levels

A thyroid antibodies test is used to diagnose and monitor autoimmune thyroid conditions. A doctor can request this test if you have symptoms of thyroid dysfunction, such as a goitre or other abnormal thyroid function test results. A thyroid antibody test requires a blood sample to be taken from a vein in your arm and sent away for laboratory analysis^[21].

You can also test your TPO levels at home with our Advanced Thyroid Test. The kit has everything you need to collect a blood sample at home and return it to one of our labs. The test can be used by anyone who wants to check if an overactive or underactive thyroid or an autoimmune condition could be causing their symptoms. It’s also suitable to monitor an existing thyroid condition.

The benefits of thyroid testing include:

• Identifying the cause of your symptoms

• Understanding if you have an underactive or overactive thyroid or an autoimmune condition

• Initiating treatment to help you feel better

Written by Leanne Edermaniger

Based in the UK, Leanne specialises in writing about health, medicine, nutrition, and fitness.

She has over 5 years of experience in writing about health and lifestyle and has a BSc (hons) Biomedical Science and an MSc Science, Communication and Society.