Celiac disease diagnosis: how gluten intolerance is detected and which tests are most accurate

Celiac disease is a chronic autoimmune disease in which the body reacts to gluten as if it were a harmful substance. In response, an immune response is triggered that damages the small intestine and prevents normal absorption of nutrients. Symptoms can be severe or almost imperceptible, so accurate diagnosis is key.

The most important rule of modern medicine: Celiac disease testing is only done when a person consumes gluten. If gluten is eliminated from the diet in advance, the tests may become unreliable and give a false-negative result. That is why the diagnosis includes several consecutive stages, each of which complements the previous one.

When to get tested for celiac disease

It is worth paying attention if a person has:

• abdominal pain, bloating, gas
• chronic diarrhea or loose stools
• iron deficiency or anemia of unknown origin
• impaired absorption of nutrients
• fatigue, irritability, mood swings
• weight loss
• frequent stomatitis
• skin rash similar to dermatitis herpetiformis
• growth retardation in children

Celiac disease can manifest with extraintestinal symptoms, including osteopenia, decreased immunity, and elevated liver enzymes. That is why international organizations include it in the differential diagnosis even when digestive problems are absent.

Blood tests: antibodies that help detect celiac disease

The first and most important stage is serological tests, i.e. the detection of antibodies in the blood. Main indicators:

• tTG-IgA — antibodies to tissue transglutaminase
• EMA-IgA — endomysial antibodies
• DGP-IgG — antibodies to deaminated gliadin peptides

tTG-IgA is the most sensitive and specific test recommended as the first step in diagnosis. EMA-IgA is performed in difficult or doubtful cases, as it has almost 100% specificity. DGP-IgG is used in children under 3 years of age and in patients with IgA deficiency.

A total IgA test is mandatory. If a genetic deficiency of immunoglobulin A is detected, then tTG-IgA and EMA-IgA values may be false - in this case, IgG tests are used.

HLA-DQ2 and HLA-DQ8 genetic tests

Genetic testing does not diagnose, but helps assess risks.

• 95% of people with celiac disease have the HLA-DQ2 gene
• most others — HLA-DQ8 gene

If both genes are missing, celiac disease is almost impossible.

Genetic testing is prescribed when:

• the person has already switched to a gluten-free diet
• blood test results are inconsistent
• risk assessment of first-degree relatives is required

Small bowel biopsy: a key step in confirming the diagnosis

A biopsy is performed during gastroscopy and allows you to assess the condition of the mucous membrane of the small intestine. Under the microscope, they look for:

• villous atrophy
• excessive number of lymphocytes
• changes in the structure of the mucous membrane

This is the «gold standard» for diagnosing celiac disease in adults. In children, diagnosis without a biopsy is sometimes allowed if antibodies are extremely high and there are typical symptoms (according to the European ESPGHAN protocols).

Why gluten should not be excluded before diagnosis

If a person switches to a gluten-free diet on their own before testing:

• antibodies may decrease
• the intestinal mucosa will temporarily recover
• the diagnosis will become impossible to confirm

To get reliable results, you must consume gluten before the test. In difficult cases, your doctor may recommend a gluten challenge — a controlled return of gluten to the diet for 6–8 weeks.

Dermatitis herpetiformis: a cutaneous manifestation of celiac disease

This is a chronic, itchy rash that often appears on the elbows, knees, buttocks, or back. A skin biopsy with immunostaining is done to confirm the diagnosis. This variant of celiac disease responds to a gluten-free diet in the same way as the classic intestinal variant.

What may resemble celiac disease

Sometimes symptoms are similar to:

• irritable bowel syndrome
• gluten allergies
• lactase deficiency
• Crohn's disease
• chronic infections
• intolerance to certain foods

Therefore, it is important to conduct a complete examination and not rely on a single test.

Table of the main methods for diagnosing celiac disease

The key methods, their purposes and limitations are summarized below.

Correct diagnosis allows you to avoid complications, reduce symptoms, and restore the body's ability to absorb necessary nutrients. The most important thing is not to start a gluten-free diet before completing all examinations, so as not to "smear" the clinical picture.