Evidence check: tTG IgA in the context of allergy

The biomarker tTG IgA (tissue transglutaminase IgA) is a well-established serological marker for diagnosing celiac disease, an autoimmune disorder triggered by gluten. In the context of allergy, however, tTG IgA is not relevant. Allergies are IgE-mediated reactions to environmental substances (e.g., pollen, foods), whereas celiac disease is a T‑cell-mediated autoimmune response to gluten. Confusion sometimes arises because both conditions can present with non-specific symptoms like abdominal pain or fatigue. A positive tTG IgA test indicates celiac disease, not an allergy. Direct-to-consumer tests offering tTG IgA should clearly communicate that this is a celiac screening test. The evidence for tTG IgA in celiac disease is strong (human-strong), but for allergies it is absent. Without specific IgE tests or skin prick tests, allergy diagnostics remain incomplete. Safety note: A positive tTG IgA result should always be followed up by a physician, as untreated celiac disease can lead to long-term complications.