Blood tests when gluten-free

People are constantly asking these questions about getting gluten/celiac blood tests.

  • I am already on a gluten-free diet so can I still have the blood test?
  • Do I need to go back onto gluten to get my celiac blood tests done?
  • Do I have to be eating gluten at the time of the blood test?

Blood tests when gluten-free

I recommend having all of your blood tests before you go gluten-free. But people often go on a gluten-free diet before they are told about gluten/celiac testing. So what should they do?

The short answer is that you do not have to be eating gluten at the time of the blood tests, as long as you have been gluten-free for only a month or two. However, the longer that you have been gluten-free, the less reliable the test results will be.
There are many issues to be considered.

What do antibody tests detect?

tTG, EMA, DGP antibody tests do not detect gluten. They are not gluten tests. They are tissue damage tests … and detect the possible damage that is caused by gluten.
The IgG-gliadin and IgA-gliadin antibody tests do not detect gluten. They are gluten reactivity tests … they indicate that gluten has stimulated the immune system and might be causing harm.

Antibody tests: tTG, EMA, DGP, IgG-gliadin, IgA-gliadin.

All of these blood tests measure antibody levels that is your body’s immune response to gluten and to any gut tissue damage. These antibodies are made by your immune cells. These blood tests do not directly measure gluten.

Antibodies continue to be made: Once your body starts to make these antibodies, you will keep on making them for many months or even for years. These antibodies are being produced by your body, constantly, all of the time. It takes months for your immune system to stop producing these antibodies. So the blood tests can be done up to 6 or even 12 months after you go gluten free and still give useful information.
The blood tests for gluten antibodies take about 6 months or longer to start going down once you go on a gluten-free diet. So, if you have just started out on a gluten-free (for a few weeks or months) then it is still okay for you to get your blood tests. You do not have to go back and eat more gluten!
Please make sure that you get all of the blood tests that you need – see the blood tests information for the details.

Off gluten for years

If you have been gluten free for many years, then your gluten antibodies (gliadin antibodies) and tissue damage antibodies (tTG, EMA, DGP) will be at low levels. It is then too late to meaningfully test for these antibodies. When you have been off gluten for several years, it may take many months of eating gluten again before your gluten and tissue-damage antibodies go high again.

Endoscopy

The above comments do not hold true for endoscopy (small bowel biopsy). This test looks for tissue evidence the actual bowel damage caused by gluten. The bowel recovers quickly (usually within a month of going gluten-free). So, you do need to have been eating gluten for many weeks at the time of the endoscopy.

HLA DQ2/DQ8 gene

This is a genetic test. This test remains the same whatever your diet and whatever your age. It never changes. So you can be gluten-free and have this test done.

See related articles:

Why you need a blood test?
Blood tests for “celiac” disease
Three Biopsy Protocol
How early can you diagnose celiac disease?
Biopsy: not the “gold standard”