Thyroid Antibodies

What is a thyroid antibody test?

A thyroid antibody test is a blood test that can help find the cause of low or high thyroid hormone levels. More specifically, it can check if you have an autoimmune thyroid disease — either Hashimoto’s disease or Graves’ disease.

Antibodies are protective proteins your immune system makes. They normally attack antigens, like bacteria and viruses. But sometimes, your immune system sends antibodies to attack healthy cells. These are called autoantibodies. Most people have small amounts of autoantibodies. But in large quantities, autoantibodies may mean you have an autoimmune condition.

High levels of thyroid antibodies appear in your blood when your immune system has attacked cells in your thyroid. Thyroid antibodies include:

• Thyroid peroxidase antibodies (TPOAb) or anti-microsomal antibodies — the main antibody that signals Hashimoto’s disease
• Thyroglobulin antibodies (TgAb)
• Thyroid stimulating immunoglobulin (TSI) — the main antibody that signals Graves’ disease
• Thyroid-stimulating hormone (TSH) receptor antibodies (TRAb) — another antibody that can be associated with Graves’ disease

Each of these antibodies has several other, similar-sounding names. Your healthcare provider may call them by a different name. Don’t hesitate to ask questions if you’re confused.

Your provider may recommend blood tests to check one or more of these thyroid antibodies if your TSH and T4 test results are abnormal.

Other reasons your provider may recommend these tests include:

• To check for thyroid cancer recurrence
• To monitor thyroid conditions during pregnancy

How do I prepare for a thyroid antibody test?

Generally, you don’t need to do anything special before a thyroid antibody test. You can eat and drink normally unless your healthcare provider tells you otherwise.

If you take any supplements that contain biotin as an ingredient, ask your healthcare provider how long to stop taking them before getting these tests. It’s possible to get inaccurate results on these tests if you’re taking biotin.

It’s a simple blood test you can get at a laboratory any time of day. A phlebotomist will use a small needle to draw blood from a vein in your arm.

What do the results of a thyroid antibody test mean?

Blood test reports, including thyroid antibody test reports, usually provide:

• The name of the blood test or what was measured in your blood
• The number or measurement of your blood test result
• The normal measurement range for that test
• Information that states if your result is negative or positive, or high or low

Thyroid antibody test results are typically listed as “negative” or “positive.” A negative result means the antibody levels are within the normal range. A positive result means the antibody levels are higher than the normal range.

What is the normal range for thyroid antibodies?

In general, normal ranges for thyroid antibodies include:

• Thyroid peroxidase antibody (TPOAb): Less than (<) 5.6 IU/ml
• Thyroglobulin antibodies (TgAb): < 4 IU/ml
• Thyroid-stimulating hormone receptor antibodies (TRAb): < 1.75 IU/L or <3.3 IU/L depending on the type of test
• Thyroid stimulating immunoglobulin (TSI): < 0.55 IU/ml

When you get the results, there’ll be information that shows what that laboratory’s normal range is. Labs may have different reference ranges. You shouldn’t compare values from one lab to normal ranges from another one.

If you have any questions about your results, ask your healthcare provider.

What does it mean if you have thyroid antibodies?

Testing positive for thyroid antibodies usually means you have an autoimmune thyroid condition. But not always — some people test positive for antibodies but don’t have thyroid disease.

You may test positive for more than one type of thyroid antibody. Having high levels means different things based on the type of antibody.

Thyroid peroxidase (TPO) antibodies

If you test positive for TPO antibodies (have a high amount) it may mean:

• You have Hashimoto’s disease (if you have high TSH levels)
• You may develop hypothyroidism later in life (if your TSH levels are currently normal or near normal)

If you test negative for TPO antibodies but have high TSH levels, it may mean something else is causing hypothyroidism.

Thyroglobulin antibodies (TgAb)

If you test positive for thyroglobulin antibodies, it may mean you have Hashimoto’s disease.

If you had thyroid surgery and radioactive iodine therapy for thyroid cancer, your provider may recommend TgAb testing. You shouldn’t have thyroglobulin in your blood after this treatment. So, the presence of TgAb — especially rising levels — may mean the cancer has come back (recurrence).

Thyroid-stimulating hormone receptor antibodies (TRAb)

If you test positive for TRAb and have low TSH, it likely means you have Graves’ disease. About 95% of people with Graves’ disease have raised TRAb.

In rare cases, you may have negative TRAb but still have Graves’ disease. In this case, a thyroid scan can diagnose it.

Thyroid stimulating immunoglobulin (TSI)

TSI is a specific type of TRAb. If you test positive for TSI, it likely means you have Graves’ disease.

If the results are abnormal what are the next steps?

If your thyroid antibody test results are abnormal, your healthcare provider will tell you about the next steps for thyroid monitoring and if you need treatment.

The main treatment for Hashimoto’s disease, if you have evidence of hypothyroidism on your labs, is a pill you take every day for the rest of your life. Graves’ disease has a few treatment options, including pills and procedures.