Celiac Disease Blood Tests: First Step in Diagnosis

Testing for celiac disease often involves five different blood tests

man looking at vial of blood
What blood tests do you need to diagnose celiac disease?. Getty Images/Tetra Images

Testing for celiac disease almost always starts with blood tests. These tests look for your body's reaction to gluten, the protein found in wheat, barley and rye that causes celiac disease.

The blood tests aren't perfect. If your celiac blood tests are negative, it means you're much less likely to have celiac disease ... but there's still a small chance that you have it. If your blood tests are positive, it means you're much more likely to have celiac disease, although you'll still (in most cases) need to undergo a medical procedure known as an endoscopy to confirm the diagnosis.

During that endoscopy, your physician will insert a tube through your stomach and into the top of your small intestine, and will then cut tiny samples from your small intestine's lining to examine under the microscope. If these tissue samples show villous atrophy, the characteristic intestinal damage found in celiac disease, then you have the condition.

Yes, it's a long process, and it all starts with the celiac blood tests.

What Blood Tests Are Performed?

The celiac disease blood tests look for antibodies that show your immune system's response to the gluten in your diet-–that's why you need to be eating gluten when you're tested for celiac disease. If you're not eating gluten at the time of testing, the blood tests will be negative even if you actually have celiac disease.

There are five blood tests you could have done when you're being tested for celiac disease:

  • AGA (antigliadin antibodies)-IgA
  • AGA-IgG
  • tTG (anti-tissue transglutaminase)-IgA
  • EMA (anti-endomysial antibodies)-IgA
  • Total serum IgA

Yes, they all look like alphabet soup. But all these tests look at specific parts of your immune system to see if your body is reacting to the gluten protein in the food you're eating.

Of all these tests, the EMA-IgA blood test is considered the most accurate blood test for celiac disease, meaning that if you have a positive result on the EMA-IgA, you very likely have celiac disease.

However, the EMA-IgA also may miss some people with celiac disease, especially if they've just begun to develop the condition.

If you're interested in the technical details: EMA stands for antiendomysial antibodies, which are antibodies produced by the body that attack the body's own tissue. IgA, or immunoglobulin A, is a common type of antibody produced by your body. Its job is to help the body identify and fight foreign invaders such as environmental toxins, bacteria and viruses.

Other Possible Celiac Tests

The blood tests known as the AGA-IgA, AGA-IgG and tTG-IgA also can indicate your body is reacting to the gluten protein ... and may even identify some people with celiac disease that the usually more accurate EMA-IgA test misses.

However, these tests also can produce some false positives, which is where the test comes back with a positive result, but the person doesn't actually have celiac disease. That's why some celiac disease experts advise performing all the tests together—you can get a more complete picture that way.

In some cases, people who have type 1 diabetes, thyroid disease, and autoimmune liver disease test positive on one of these tests, the tTG-IgA test, due to their other conditions. tTG stands for tissue transglutaminase, an enzyme normally present in the intestines. 

A positive tTG-IgA blood test indicates the body is creating antibodies to its own tissues, which can happen in response to gluten ingestion. However, it doesn't always mean you have celiac disease, especially if you have one of the other conditions listed. So if you have any of those conditions, your physician most likely will look more closely at the results of the other celiac disease blood tests.

Finally, the celiac blood test panel usually includes a test looking at how much of one particular antibody, immunoglobulin A, your body makes. This is important because people who are low in this particular antibody (known as IgA) may have negative results on the celiac disease blood tests, even if they actually have the condition.

And, this is even more important because people with celiac disease suffer from this situation, known as IgA deficiency, about 10 to 15 times more frequently than people in the general population.

Some physicians also use one of these tests—the antigliadin antibodies-IgG, or the AGA-IgG—to screen people for non-celiac gluten sensitivity. However, researchers have shown it's not particularly accurate for that purpose, and as of now, scientists haven't developed an accurate test for gluten sensitivity.

Celiac Gene Testing

Some physicians also recommend testing for particular genes that increase your risk of having celiac disease. If you've already begun the gluten-free diet, this may be the only test your doctor recommends running (the tests I describe above aren't accurate unless you're eating gluten).

The celiac gene tests don't look for antibodies to gluten; instead, they look for two specific genes, HLA-DQ2 and HLA-DQ8, that have been associated with celiac disease. Your genes don't change, even if you're eating gluten-free.

Now, a positive celiac gene test doesn't mean you have celiac disease-–it simply means you have the "right" genes to possibly develop the condition. If your other blood tests are negative but your gene test is positive, you and your doctor might decide you should stop eating gluten for a trial period to see if any celiac disease symptoms clear up.

Source:

Serologic and Genetic Testing. Celiac Disease Center at Columbia University Medical Center.

University of Maryland Center for Celiac Research. Celiac Disease: Frequently Asked Questions fact sheet

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