Thyroid Antibodies Test: TPO, Tg, TSI and TRAb Levels Explained
Updated: 4 days ago
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: November 2026 · How we review
Quick Answer: What is a thyroid antibody test?
A thyroid antibody test is a blood test that checks whether your immune system is making antibodies against your thyroid. High levels usually point to an autoimmune thyroid disease, either Hashimoto's disease (underactive thyroid) or Graves' disease (overactive thyroid). It is often ordered when TSH or T4 results are abnormal. [1]
What the research says
TRAb tests are highly accurate for Graves' disease. A meta-analysis of 21 studies found second- and third-generation TRAb immunoassays had pooled sensitivity of 97.1% and 98.3%, with specificity of 97.4% and 99.2%. (Tozzoli et al., Autoimmunity Reviews, 2012) [2]
Thyroid antibodies matter in pregnancy. Among 31 studies with 12,126 women with normal thyroid function, thyroid autoantibodies were linked to more than three times the odds of miscarriage (odds ratio 3.90) in cohort studies and double the odds of preterm birth. (Thangaratinam et al., BMJ, 2011) [3]
Key takeaways
Thyroid antibodies show whether your immune system is attacking your thyroid. [1]
The four main types are TPOAb, TgAb, TSI and TRAb. [1]
No fasting is needed, but tell your provider if you take biotin. [1]
A positive result usually means Hashimoto's or Graves' disease, but not always. [1]
About 95% of people with Graves' disease have raised TRAb. [1]
What are thyroid antibodies?
Antibodies are protective proteins your immune system makes to fight germs like bacteria and viruses. Sometimes the immune system makes antibodies that attack healthy cells instead. These are called autoantibodies. [1]
Most people have small amounts of autoantibodies, but large amounts can mean an autoimmune condition. High thyroid antibody levels appear when your immune system has attacked cells in your thyroid. [1]
Antibody | Main link |
Thyroid peroxidase antibodies (TPOAb), also called anti-microsomal antibodies | The main antibody that signals Hashimoto's disease |
Thyroglobulin antibodies (TgAb) | Hashimoto's disease; also used to monitor thyroid cancer |
Thyroid-stimulating immunoglobulin (TSI) | The main antibody that signals Graves' disease |
TSH receptor antibodies (TRAb) | Also associated with Graves' disease |
Sources: [1]
Each antibody has several similar-sounding names, so ask your provider if a name on your report is confusing. [1]
Why is a thyroid antibody test done?
Your provider may order one or more of these tests if your TSH and T4 results are abnormal, to find out whether an autoimmune disease is the cause. Other reasons include: [1]
Checking whether thyroid cancer has come back
Monitoring thyroid conditions during pregnancy
How do you prepare for the test?
You usually do not need to do anything special and can eat and drink normally unless told otherwise. [1]
If you take supplements that contain biotin, ask your provider how long to stop them first, because biotin can make these results inaccurate. [1]
The test is a simple blood draw from a vein in your arm, and you can have it any time of day. [1]
What are normal thyroid antibody levels?
Results are usually reported as negative (within the normal range) or positive (higher than normal). In general, normal ranges are: [1]
Antibody | Typical normal range |
TPOAb | Less than 5.6 IU/mL |
TgAb | Less than 4 IU/mL |
TSI | Less than 0.55 IU/mL |
TRAb | Less than 1.75 IU/L or less than 3.3 IU/L, depending on the test |
Sources: [1]
Labs use different reference ranges, so compare your result only with the range on your own report. [1]
What do positive results mean?
Testing positive usually means an autoimmune thyroid condition, but some people have antibodies without thyroid disease. You may also test positive for more than one antibody. [1]
TPO antibodies: With high TSH, this suggests Hashimoto's disease. With normal or near-normal TSH, it may mean you develop hypothyroidism later in life. If TPO is negative but TSH is high, something else may be causing hypothyroidism. [1]
Thyroglobulin antibodies: A positive result may mean Hashimoto's disease. After thyroid surgery and radioactive iodine for thyroid cancer, TgAb, especially rising levels, may mean the cancer has come back. [1]
TRAb: With low TSH, a positive result likely means Graves' disease. About 95% of people with Graves' disease have raised TRAb. Rarely, TRAb is negative in Graves' disease, and a thyroid scan can confirm it. [1]
TSI: A specific type of TRAb. A positive result likely means Graves' disease, and TSI is the recommended lab test because TRAb tests can sometimes be inaccurate. [1]
What happens if your results are abnormal?
Your provider will explain the next steps for monitoring and whether you need treatment. If you have Hashimoto's disease with signs of hypothyroidism, the main treatment is a daily pill taken for life. Graves' disease has several options, including pills and procedures. [1]
Conclusion
A thyroid antibody test helps explain why your thyroid hormone levels are off by showing whether an autoimmune disease is involved. TPO and Tg antibodies point toward Hashimoto's disease, while TSI and TRAb point toward Graves' disease.
If your results are abnormal, ask your provider which antibodies were tested and what they mean together with your TSH and T4 levels.
Keep learning: Read our guide to hypothyroidism or learn about Graves' disease. For more background, see MedlinePlus on thyroid antibodies.
FAQ
What is a thyroid antibody test?
It is a blood test that checks for antibodies that attack the thyroid, to find autoimmune thyroid disease. [1]
What are the main thyroid antibodies?
The main ones are TPO antibodies, thyroglobulin antibodies (TgAb), thyroid-stimulating immunoglobulin (TSI) and TSH receptor antibodies (TRAb). [1]
What does a high TPO antibody level mean?
With high TSH it suggests Hashimoto's disease; with normal TSH it may mean hypothyroidism later in life. [1]
Which antibody test confirms Graves' disease?
TSI is the recommended lab test, and about 95% of people with Graves' disease have raised TRAb. [1]
Do I need to fast for a thyroid antibody test?
No. You can usually eat and drink normally, but ask about stopping biotin supplements first. [1]
What is the normal range for TPO antibodies?
In general, less than 5.6 IU/mL, though ranges vary between labs. [1]
Can you have thyroid antibodies without thyroid disease?
Yes. Some people test positive for thyroid antibodies but do not have thyroid disease. [1]
Why are thyroglobulin antibodies checked after thyroid cancer?
After surgery and radioactive iodine, rising TgAb levels may mean the cancer has come back. [1]
Why would a thyroid antibody test be done in pregnancy?
It may be used to monitor thyroid conditions during pregnancy. [1]
What happens if my thyroid antibodies are high?
Your provider will plan monitoring and decide whether you need treatment, such as a daily pill for Hashimoto's-related hypothyroidism. [1]
Related Reading
Hypothyroidism: Symptoms, Causes & Treatment Guide explains the underactive thyroid that TPO antibodies often signal.
Hyperthyroidism: Symptoms, Causes & Treatment covers the overactive thyroid linked to TSI and TRAb.
Graves' Disease: How an Overactive Immune System Drives an Overactive Thyroid, and What Treatment Can Do describes the autoimmune disease TRAb and TSI tests confirm.
Thyroid Disease: Types, Symptoms, Tests and Treatment gives an overview of the conditions thyroid antibodies help diagnose.
Thyroid Cancer: Symptoms, Causes, Diagnosis and Treatment — What You Need to Know explains the cancer monitored with thyroglobulin antibodies.
References
Cleveland Clinic. Thyroid Antibodies: What They Are, Types, Levels & Tests. Cleveland Clinic. Last updated February 12, 2025. https://my.clevelandclinic.org/health/diagnostics/thyroid-antibodies
Tozzoli R, Bagnasco M, Giavarina D, et al. TSH receptor autoantibody immunoassay in patients with Graves' disease: improvement of diagnostic accuracy over different generations of methods. Systematic review and meta-analysis. Autoimmun Rev. 2012;12(2):107-113. PMID 22776786. https://doi.org/10.1016/j.autrev.2012.07.003
Thangaratinam S, Tan A, Knox E, et al. Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence. BMJ. 2011;342:d2616. PMID 21558126. https://doi.org/10.1136/bmj.d2616
Medical disclaimer
This article is for general education only and does not replace advice from a qualified healthcare professional. Talk to your doctor about your own diagnosis and treatment, and seek emergency care right away for severe or sudden symptoms.
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