Do you suspect you might have celiac disease? Or are there already family members affected? Then here you will find the exact procedure to get a definitive answer as to whether celiac disease is present or not. Below, you can also download a diagnostic checklist with all the important steps to check off.

What do you absolutely need to keep in mind before celiac disease testing?

If you suspect you may have celiac disease, the most important requirement for an accurate diagnosis is that you must not under any circumstances reduce gluten in your diet. Well-meaning advice—even from doctors, alternative practitioners, or friends—to try an elimination diet is unfortunately counterproductive to the goal of obtaining a reliable result as soon as possible. This is because the changes in the blood and the intestinal mucosa gradually recede under a gluten-free diet and can then no longer be reliably detected. If you have already been largely avoiding gluten for more than 4 weeks, it is quite possible that the wrong conclusions will be drawn from the tests, namely that you do not have celiac disease. If this were only due to the trial diet, that would obviously be disadvantageous for you. Therefore:

I have often been in contact with people affected who had already been avoiding gluten for a long period without a sound diagnosis. Because of this avoidance, they often report a significant improvement in their symptoms. But they never actually knew whether they had celiac disease or not. However, as soon as they notice positive changes, they are usually no longer willing to consume gluten again – even if an accurate diagnosis is still pending.

I can certainly understand that, because who would voluntarily expose themselves to it again once they are feeling better, knowing what symptoms are in store for them. Nevertheless, it is important to know whether you have celiac disease or if the symptoms had other causes. To ensure this doesn’t happen to you, you should start on the right path from the beginning.

Step 1: Antibody test

The simplest and therefore first diagnostic step should be a blood test for celiac disease antibodies. In this case, the tissue transglutaminase IgA antibody (abbreviated as tTG-IgA-Ab) together with the determination of the total IgA level is usually sufficient and relatively cost-effective. Total IgA is important because a deficiency of antibodies from this subgroup is the most common (often undetected) immune deficiency in our population. Affected individuals do not produce sufficient IgA antibodies and, in the case of celiac disease, do not produce increased tissue transglutaminase IgA antibodies either. Without knowledge of an IgA deficiency,
an inconspicuously low tTG-IgA test is interpreted as "no celiac disease." However, in the case of an IgA deficiency, this might be a misinterpretation. I explain this special situation in more detail in this article.

Normally, total IgA will be within the normal range and the transglutaminase IgA antibody can be interpreted directly:

- An inconspicuous value (i.e., within the normal range) means that celiac disease is rather unlikely.
- An elevated value (above the normal range) is suspicious and should be investigated further.

Step 2: Gastroscopy with small intestine biopsy

The next step, while still on a gluten-containing diet, would be a referral to a gastroenterologist to perform a gastroscopy. During this procedure, samples are taken from the duodenum to examine whether the typical changes in the mucous membrane can be detected.

The pathologist, the medical specialist for the assessment of tissues and cells, examines the small tissue samples taken closely under the microscope. In doing so, they determine whether the mucous membrane shows normal structures or exhibits abnormalities typical of celiac disease.

The small intestinal mucosa is folded to increase its surface area. In this process, the villi protrude as elevations into the interior of the intestine. In the crypts, the depressions, new cells are produced to constantly renew the mucous membrane. Typical of celiac disease is the shortening of the villi, which can vary in severity.

Important to know!

However, there are also other diseases that present a similar picture in the mucous membrane, which should be taken into account during diagnosis. This applies in particular if no celiac antibodies can be detected.

Step 3: Synthesis of findings

Once all examinations are complete, a physician must consolidate them and determine whether everything now points to celiac disease. In many cases, this will be the general practitioner, as gastroenterologists often only perform the endoscopies and then refer the patients back to their primary care physician.

Your GP should then inform you of the diagnosis and initiate further necessary steps: this includes further blood tests to see which vitamins and minerals you are lacking due to celiac disease and which organs are affected (e.g., liver, thyroid). And, of course, professional nutritional counseling should guide you on your gluten-free path.

Here is another brief overview of the examinations that must be carried out to determine celiac disease:

1.     Blood test for tissue transglutaminase IgA antibodies (TTG-IgA-Abs) and total IgA
2.     Performing a gastroscopy with the collection of a sufficient number of samples (at least 5-6) from various locations in the duodenum

If both tests are abnormal, i.e., the antibodies are elevated above the normal range and the mucous membrane shows villous atrophy, the diagnosis is confirmed.