🧪 Thyroid Antibody Tests Explained

Thyroid Antibody Tests Explained: Learn what thyroid antibody tests mean, why doctors order them, and how they help diagnose autoimmune thyroid conditions like Hashimoto’s disease and Graves’ disease. 

Finding Autoimmune Thyroid Problems 

So far we’ve talked about:

• TSH
  
  

• Free T4
  
  

• Free T3
  
  

Now we’re going to cover a different kind of test:

➡ Thyroid antibody tests

These tests help explain why a thyroid problem is happening.

🔎 What Are Thyroid Antibodies? 

Antibodies are proteins made by your immune system.

Their normal job is to attack things like:

• Viruses
  
  

• Bacteria
  
  

• Germs
  
  

But sometimes the immune system gets confused and attacks healthy parts of your body.

When it attacks the thyroid, it can cause autoimmune thyroid disease.

🧠 Why Antibody Tests Matter 

Standard thyroid tests (TSH, Free T4, Free T3) tell us:

• If the thyroid is too slow
  
  

• If the thyroid is too fast
  
  

But they don’t tell us why.

Thyroid antibody tests help answer that question.

📌 The Most Common Thyroid Antibody Tests 

There are three main ones doctors check:

1. TPO Antibodies (Thyroid Peroxidase Antibodies)
   
   

2. Thyroglobulin Antibodies (TgAb)
   
   

3. TSI or TRAb (Thyroid Stimulating Immunoglobulins / TSH Receptor Antibodies)
   
   

Each one points to different thyroid conditions.

🦋 TPO Antibodies (Anti-TPO) 

What This Test Looks For

TPO antibodies are the most commonly checked thyroid antibodies.

A positive TPO test usually means:

➡ Hashimoto’s disease
(the most common cause of hypothyroidism)

What It Means

If TPO antibodies are positive:

• Your immune system is attacking your thyroid
  
  

• Over time this can make the thyroid underactive
  
  

• It confirms an autoimmune cause
  
  

Many people with high TPO antibodies eventually develop hypothyroidism.

🧬 Thyroglobulin Antibodies (TgAb) 

This test is often checked along with TPO.

Positive TgAb can also suggest:

• Hashimoto’s disease
  
  

• Other autoimmune thyroid conditions
  
  

It is especially useful when TPO is negative but autoimmune thyroid disease is still suspected.

⚡ TSI / TRAb Antibodies 

These antibodies are different.

They are usually checked when doctors suspect:

➡ Graves’ disease (overactive thyroid)

What a Positive TSI Means

If TSI or TRAb is positive:

• The immune system is stimulating the thyroid
  
  

• The thyroid is pushed to make too much hormone
  
  

• This confirms autoimmune hyperthyroidism
  
  

This is the most common cause of high thyroid levels.

🧩 How Antibody Tests Fit With Other Results 

Here are common combinations: 

Pattern 1

High TSH + Positive TPO

• Confirms Hashimoto’s hypothyroidism

Pattern 2

Low TSH + Positive TSI

• Confirms Graves’ disease (hyperthyroidism)

Pattern 3

Normal TSH + Positive TPO

This can mean:

• Early autoimmune thyroid disease
  
  

• Higher risk of future thyroid problems
  
  

• Need for occasional monitoring

❓ Can You Have Antibodies and Normal Thyroid Levels? 

Yes!

Some people have positive antibodies but:

• Normal TSH
  
  

• Normal Free T4
  
  

• No symptoms
  
  

This means the immune system is active, but thyroid function is still okay.

Doctors often just monitor in these cases.

🕒 Do Antibody Levels Go Away? 

Usually:

• Antibodies can stay positive for years
  
  

• Levels may go up and down
  
  

• Treatment focuses on thyroid function, not the antibody number
  
  

Doctors rarely treat based only on antibody levels.

🩺 When Doctors Order Antibody Tests 

Antibodies are commonly checked when:

• TSH is abnormal
  
  

• Symptoms suggest autoimmune thyroid disease
  
  

• A cause needs to be confirmed
  
  

• Someone has a family history of thyroid problems
  
  

• A person is pregnant or planning pregnancy

🧭 What Usually Happens Next 

If antibodies are positive:

• Doctors look at TSH and Free T4
  
  

• Decide whether treatment is needed
  
  

• Plan regular monitoring
  
  

• Discuss long-term expectations

🔑 Big Takeaways 

Antibody tests help find the cause of thyroid problems

Positive TPO → usually Hashimoto’s

Positive TSI → usually Graves’ disease

Antibodies can be positive even with normal thyroid levels

Treatment depends on hormone levels, not just antibodies

Coming Up Next 

The next page will explain:

➡ Hypothyroidism Explained (Low Thyroid)

We’ll connect symptoms, tests, and treatment all together.