Testing for celiac disease almost always starts with blood tests. If your celiac blood tests are positive, you'll likely undergo an endoscopy and a biopsy to look for damage to your intestinal villi. (If the tests are negative, your doctor still may recommend an endoscopy with biopsy, as the blood tests aren't perfect.) If the endoscopy shows that your villi are damaged in a particular pattern, you will be diagnosed with celiac disease.
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. If you're not eating gluten at the time of testing, your system won't be producing any antibodies for the blood tests to identify.
There are five blood tests you could have done when you're being tested for celiac disease:
- AGA (antigliadin antibodies)-IgA
- tTG (anti-tissue transglutaminase)-IgA
- EMA (anti-endomysial antibodies)-IgA
- Total serum IgA
Of these, the EMA-IgA blood test is considered the most specific to celiac disease, meaning that if you have a positive result on that test, you almost certainly have celiac disease. However, the EMA-IgA also may miss some people with the condition, especially people whose intestinal villi haven't been completely destroyed.
On the other hand, the AGA-IgA, AGA-IgG and tTG-IgA can produce some false positives, but also may identify people with celiac disease that the EMA-IgA test misses. That's why some celiac disease experts advise performing the entire panel, instead of just one or two of the tests.
Some people who have type 1 diabetes, thyroid disease, and autoimmune liver disease test positive on the tTG-IgA test due to their other autoimmune conditions, so if you have any of those, your physician most likely will look more closely at the results of the other celiac disease blood tests.
The celiac blood test panel includes the total serum IgA test because some people are IgA-deficient. If you have a very low total serum IgA, that can invalidate the three blood tests that rely on your IgA levels. People with celiac disease suffer from low total IgA levels about 10 to 15 times more frequently than people in the general population.
Celiac Gene Blood Tests
Some physicians also recommend testing for particular genes that increase susceptibility to celiac disease, especially in cases where the individual already has begun the gluten-free diet. The celiac gene blood 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.
A positive celiac gene test doesn't mean you have celiac disease -– it simply means you have the potential to 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.
Serologic and Genetic Testing. Celiac Disease Center at Columbia University Medical Center. Accessed Oct. 4, 2010.
Celiac Disease: Frequently Asked Questions. University of Maryland Center for Celiac Research. Accessed Oct. 4, 2010.