Thyroid Antibodies: What TPO and TgAb Tests Reveal About Autoimmune Thyroid Disease

Quick answer

Anti-thyroid peroxidase, or TPO, and anti-thyroglobulin, or TgAb, are two thyroid antibodies. Both point to Hashimoto's disease, which causes an underactive thyroid. TSH receptor antibodies, or TRAb, point to Graves' disease instead. Graves' disease causes an overactive thyroid. A thyroid antibody test can turn positive years before TSH or thyroid hormone levels change. That gives you an early view of where your thyroid is heading.

What thyroid antibodies are

Your immune system sometimes mistakes your thyroid for a threat. That is how autoimmune thyroid disease starts. Your body builds antibodies to attack your own thyroid.

Over time, they do one of two things. They can damage thyroid tissue, which causes Hashimoto's disease. Or they can overstimulate it, which causes Graves' disease. They stay in your blood for years. They usually show up long before you feel any symptoms or see any change in TSH.

Anti-thyroid peroxidase (TPO) antibodies

TPO is an enzyme. Your thyroid needs it to make hormone. This test checks for antibodies against it.

Reference range: under 34 IU/mL. This can vary slightly by lab.

If this comes back positive:

• It most often points to Hashimoto's disease.
• Around 10 to 15 percent of adults without symptoms test positive. This is more common in women.
• It signals a much higher risk of an underactive thyroid. That risk runs two to four times higher, over the next ten to twenty years.
• It is often the first sign of trouble ahead. It can show up years before TSH changes.

What your doctor may do:

• Watch your TSH more closely. Check every six to twelve months.
• If TSH is also high, use the antibody result to help decide on treatment.
• If you are planning a pregnancy, doctors use a tighter treatment threshold. This applies to a mildly underactive thyroid.

Anti-thyroglobulin (TgAb) antibodies

Thyroglobulin is a protein your thyroid uses to build hormone. This test checks for antibodies against it.

Reference range: under 40 IU/mL. This can vary slightly by lab.

If this comes back positive:

• It is also linked to Hashimoto's disease. It often shows up alongside a positive TPO.
• On its own, a positive TgAb is a weaker signal than a positive TPO.
• It matters most in thyroid cancer follow-up. TgAb can interfere with a different tumor marker test.

What your doctor may do: much the same as with TPO. Expect closer monitoring, and it may support treating a mildly underactive thyroid.

TSH receptor antibodies (TRAb)

TRAb attaches to the TSH receptor on your thyroid cells. Instead of blocking your thyroid, it pushes your thyroid to overwork.

Reference range: under 1.75 IU/L. This can vary slightly by lab.

If this comes back positive:

• It confirms Graves' disease. This is the most common cause of an overactive thyroid.
• It runs strongly positive during active Graves' disease.
• It helps tell Graves' disease apart from other causes of an overactive thyroid.
• A high level can predict a higher chance of relapse after antithyroid medicine.

What your doctor may do:

• Confirm Graves' disease. This happens when you also have hyperthyroid symptoms and matching blood work.
• Watch closely during pregnancy. A high TRAb can affect the baby.
• Track it during treatment. A falling TRAb is a good sign that treatment is working.

Why antibodies matter even with a normal TSH

Antibodies can test positive years before TSH moves. The usual path looks like this.

1. Antibodies positive, TSH normal. Early disease, no symptoms yet, but real future risk.
2. Antibodies positive, TSH 2.5 to 4.5. A borderline, mild pattern starting to show.
3. Antibodies positive, TSH 4.5 to 10. A clear mild underactive thyroid.
4. Antibodies positive, TSH over 10. A full underactive thyroid, with a known autoimmune cause.

Knowing this early changes the plan at every stage. This matters most for women planning a pregnancy. A positive result lowers the treatment threshold for a mildly underactive thyroid.

Who should get a thyroid antibody test?

Strongly consider testing TPO and TgAb if any of these apply to you.

• Your TSH sits in the 2.5 to 10 mIU/L range.
• You have thyroid symptoms, and your TSH is high-normal.
• Autoimmune thyroid disease runs in your family.
• You have another autoimmune condition. Examples include type 1 diabetes, celiac disease, vitiligo, or rheumatoid arthritis.
• You are planning a pregnancy.
• You gave birth within the last 12 months.
• You have had an unexplained miscarriage or trouble getting pregnant.

Consider testing TRAb in a few specific cases.

• You have hyperthyroid symptoms or a suppressed TSH.
• Your doctor needs to tell Graves' disease apart from another cause.
• You are pregnant and have a history of Graves' disease.

What to do with positive antibodies and a normal TSH

This is a common combination. Three things matter here.

Monitoring. Recheck TSH, Free T4, and Free T3 every six to twelve months. The trend over time matters more than any single result.

Lifestyle steps that may help. Some habits may slow autoimmune progress, though the evidence varies in strength.

• Correct a low vitamin D level. It supports healthy immune function.
• Selenium, at about 200 micrograms a day, may modestly lower TPO levels in some people. The research here is mixed.
• Cutting gluten has limited evidence for people without celiac disease. Still, a trial elimination helps some.
• Manage stress and get enough sleep. Both worsen autoimmune conditions in general.
• Support your gut health. New research links gut health to thyroid autoimmunity.
• Avoid very high iodine intake. This can speed up autoimmune thyroid damage.

Pregnancy planning. If you are trying to get pregnant, or recently gave birth, treatment thresholds shift. Talk this through with your doctor.

Common patterns

Early Hashimoto's disease. TPO is positive. TSH is normal or high-normal, between 2.5 and 4.5. Free T4 and Free T3 look normal. Often no symptoms yet. Action: monitor, and try helpful lifestyle steps.

Established Hashimoto's, mild. TPO is positive, often strongly. TSH sits between 4.5 and 10. Free T4 is normal or low-normal. Action: discuss treatment based on symptoms, fertility plans, and age.

Established Hashimoto's, full. TPO is positive. TSH is over 10. Free T4 is low. Action: start levothyroxine treatment.

Graves' disease. TRAb is positive. TSH is suppressed. Free T4 and Free T3 are high. Action: treatment led by your doctor, which may include medicine, radioactive iodine, or surgery.

Postpartum thyroiditis. TPO is often positive. TSH swings, sometimes showing a brief overactive phase followed by an underactive one. Action: monitor closely, and treat based on which phase you are in.

Why antibody testing gets skipped

Cost is the main reason. Adding these tests raises the price of a panel. Many standard checkup packages leave them out. Most doctors agree that TPO should be included, at least for women. The extra cost just keeps it from being routine everywhere.

Want the fuller picture? See our guide on thyroid testing in the Philippines. It covers this alongside TSH, T3, and T4.

What your &you Labs panel includes

Thyroid health is one of ten categories a &you Labs panel checks. Your report shows the standard lab range and the healthy target range side by side. You also get a doctor's plain language plan.

You can book your &you Labs panel to see where your own thyroid markers fall.

Frequently asked questions

My TPO is positive, but everything else looks normal. What does that mean?

This is early autoimmune thyroid disease. You do not have an underactive thyroid today. But your future risk is real. Monitor TSH every six to twelve months, and try helpful lifestyle steps where you can. No medicine is needed at this stage.

Can thyroid antibodies go away over time?

Sometimes, most often with steady lifestyle changes, correcting low vitamin D, or treating an underlying cause. Levels can rise and fall. The trend over time tells you more than any single test.

Does a positive antibody test mean I will definitely get thyroid disease?

No. Most people with positive antibodies see slow changes. Some never develop full disease at all. A positive result means higher risk, not a guarantee.

Should I take selenium if my TPO is high?

Some evidence supports about 200 micrograms of selenium a day. This may help lower TPO antibodies in some people. Brazil nuts are a natural source. One or two nuts a day is plenty. Talk to your doctor before starting any supplement.

How often should I retest my antibodies?

After a first positive result, retest once at six to twelve months. This confirms the pattern. After that, testing every one to two years is reasonable unless something changes.

Key takeaways

• TPO and TgAb antibodies point to Hashimoto's disease. TRAb points to Graves' disease.
• Antibodies can test positive years before TSH or thyroid hormone levels change.
• A positive antibody result changes how your doctor manages a mildly underactive thyroid. This matters even more if you are planning a pregnancy.
• Some lifestyle steps may slow autoimmune progress. These include correcting vitamin D, taking selenium, managing stress, and sleeping well.
• Consider testing if you are a woman in your 30s or older. The same goes for a family history, another autoimmune condition, or a borderline TSH.