Between 80% and 90% of patients go undiagnosed. 

How Is Celiac Disease Diagnosed?

Celiac disease is an autoimmune condition triggered by gluten exposure. Because symptoms can be vague or overlap with irritable bowel syndrome, proper testing is essential.

1. Testing must be done while eating gluten

This is critical.
If a patient has already removed gluten from the diet, blood tests and biopsies can appear normal. For accurate results, gluten must be consumed regularly for several weeks prior to testing.

2. Blood (serologic) testing

The first step is blood testing for celiac-associated antibodies. Common tests include:

  • Tissue transglutaminase IgA (tTG-IgA) – the primary screening test

  • Total serum IgA – to rule out IgA deficiency

  • Deamidated gliadin peptide (DGP) antibodies – sometimes used in children or equivocal cases

A positive result suggests immune reactivity to gluten, but does not by itself confirm the diagnosis.

3. Small intestinal biopsy

If blood tests are positive, the diagnostic gold standard is an upper endoscopy with biopsy of the small intestine. In celiac disease, biopsies typically show:

  • Villous atrophy

  • Crypt hyperplasia

  • Increased intraepithelial lymphocytes

These findings confirm intestinal damage caused by gluten exposure

4. Genetic testing (optional, not diagnostic)

Testing for HLA-DQ2 or HLA-DQ8 can be useful in select cases.

  • If neither gene is present, celiac disease is very unlikely.

  • If present, it only indicates genetic susceptibility—not active disease.

5. Response to a gluten-free diet

Symptom improvement on a gluten-free diet supports the diagnosis but should not replace proper testing, since many non-celiac conditions also improve when gluten is removed from the diet.