Celiac disease is primarily tested through a combination of blood tests and intestinal biopsies.
Blood Tests
The first step usually involves blood tests that measure levels of specific antibodies related to celiac disease, such as tissue transglutaminase IgA antibodies (tTG-IgA) and total IgA. These antibodies are elevated in people with untreated celiac disease who are consuming gluten. For accurate results, the person must be on a gluten-containing diet prior to testing. In young children, additional antibodies like deamidated gliadin IgA and IgG may be tested. Blood tests alone cannot confirm celiac disease, because false positives and false negatives are possible, especially in people with other autoimmune conditions.
Intestinal Biopsy
If blood tests suggest celiac disease, a small intestine biopsy is the gold standard for diagnosis. This is done via an upper endoscopy where small tissue samples from the small intestine are taken and examined under a microscope for villous atrophy and other signs of intestinal damage characteristic of celiac disease. The biopsy confirms whether the immune reaction to gluten has caused intestinal damage.
Additional Tests
- Genetic testing for HLA-DQ2 and HLA-DQ8 genes can help rule out celiac disease if these genes are absent, but having the genes does not confirm the disease by itself.
- In cases of dermatitis herpetiformis (a skin manifestation of celiac disease), a skin biopsy may be performed.
- Nutritional assessments may be done to check for deficiencies related to malabsorption.
In summary, diagnosis involves initial antibody blood testing while on gluten, followed by confirmation with an intestinal biopsy if tests suggest celiac disease, supported by genetic and occasionally skin tests when needed.
