Diagnosing celiac disease after going on a GF diet

Katarina Mollo MEd, RDN, LDN
Q: Could you clarify for me the different ways to test for celiac disease? If you have been GF for a while, would a biopsy then not indicate celiac disease? If you could educate me on the diagnostic tests for celiac disease AFTER you have been GF for a period it would be greatly appreciated!


Generally, testing for celiac disease is done in two steps, starting with a blood test to look for celiac-related antibodies, also referred to as a “celiac panel.” A celiac panel should include total IgA and tissue transglutaminase IgA (tTG IgA). It also often includes anti-endomysial antibody (EMA) and anti-deaminated gliadin peptide (anti-DGP).

If the blood test is positive, or there is other strong evidence of celiac disease then an endoscopy with a biopsy of the small intestine is done. This is considered the “gold standard” for diagnosing celiac disease. During an endoscopy, a scope with a small camera at the end is passed down the mouth, esophagus, stomach and into the small intestine. The doctor will look for damage and inflammation of the intestinal lining and several samples are taken.

It is very important that you do not start a gluten-free diet before testing and diagnosis. Once on a gluten-free diet, antibodies to gluten will start to drop in the blood and the intestine will start to heal and there is a risk of a false negative result on both the blood test and endoscopy.

If you are already on a gluten-free diet then you should contact a gastroenterologist specializing in celiac disease. They would most likely put you on a gluten challenge diet so that they can determine if you have celiac disease. The only way to diagnose celiac disease is to eat gluten. But you would do this under their care.

Read more about how to find a doctor specializing in celiac disease: https://nationalceliac.org/celiac-disease-questions/is-there-a-state-by-state-register-that-lists-gastroenterologists-who-specialize-in-celiac-disease/

In terms of how much gluten you have to eat prior to testing, it seems to vary from doctor to doctor. I know that Dr. Fasano's patients at the Mass General Center for Celiac Research and Treatment have to eat at least a cracker a day for a month for an initial antibody test, but they prefer at least three months of eating gluten to be sure of the accuracy of the test.

At the University of Chicago Celiac Disease Center, they advise that patients eat half a slice of bread for 12 weeks prior to blood work and two weeks ahead of an endoscopy.

The Celiac Center at Beth Israel advise that gluten should be consumed for six to eight weeks before testing. (2)

There is also a genetic test that tests for genes associated with celiac disease (HLA DQ 2 & HLA DQ 8), however it can only rule out celiac disease. A genetic test can sometimes be used as a first step to determine if you should go on with further testing. It won't tell you if you have celiac disease, only if you carry the gene. But if you do not have the gene then celiac disease is very unlikely.

Read more about testing here: https://nationalceliac.org/celiac-disease-questions/tests-for-celiac-disease/

Check out this infographic for the different celiac related tests:


  1. National Celiac Association. Gluten-Free, Off to A Fresh Start. Presentation. Updated September, 2020.
  2. Bean K. Diagnosis Dilemma. Gluten-Free Living. Gluten-Free Living Website: https://www.glutenfreeliving.com/gluten-free/gluten-sensitivity/diagnosis-dilemma/ Published May 5, 2016.

Note: This information is provided by NCA and Katarina Mollo MEd, RDN, LDN, NCA's Director of Education. This information is meant for educational purposes only and is not intended to substitute for personalized medical advice or replace any medical advice provided directly to you by your health care provider. No liability is assumed by the NCA or Katarina Mollo, MEd, RDN, LDN by providing this information.

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