Tissue transglutaminase IgA (tTG IgA) is the gold-standard blood test for coeliac disease. It detects IgA-class antibodies directed against tissue transglutaminase 2, an enzyme that modifies gliadin — a component of gluten — into a form that triggers an immune response in people with coeliac disease. The antibody is produced in the small intestinal lining as part of the immune attack on intestinal tissue.

In coeliac disease, ingestion of gluten triggers the immune system to produce tTG IgA antibodies and attack the intestinal lining, causing progressive damage to the villi — small finger-like projections responsible for nutrient absorption. tTG IgA is the single most sensitive and specific blood test for coeliac disease in IgA-sufficient individuals, with sensitivity above 90% and specificity above 95% when combined with compatible symptoms.