Tissue Transglutaminase Antibody, IgA (tTG-IgA)
Other marker
Tissue Transglutaminase Antibody IgA
Tissue Transglutaminase Antibody, IgA (tTG-IgA)
The first-line blood test for coeliac disease. It measures IgA antibodies against tissue transglutaminase, the enzyme targeted by the autoimmune response to gluten. It has high sensitivity and specificity, but depends on the person producing normal amounts of IgA.
PED Notes
The standard coeliac screen, relevant to athletes with unexplained GI symptoms, iron-deficiency anaemia, or difficulty gaining weight. Two caveats matter for this group. First, the test is only valid if the person is eating gluten: physique athletes who have already cut gluten can test falsely negative. Second, it must be interpreted alongside total IgA, because selective IgA deficiency (about 1 in 500 people) makes tTG-IgA falsely negative, in which case an IgG-based test (deamidated gliadin IgG) is used instead.
When high
When elevated (>20 U/mL, positive; strongly positive when >10x the upper limit):
- Highly suggestive of coeliac disease. In adults, confirm with duodenal biopsy while still eating gluten; some paediatric pathways allow diagnosis on very high antibody titres without biopsy
- Do not start a gluten-free diet before confirmatory testing, as it will lower the antibodies and can obscure the diagnosis
- Screen for the consequences of malabsorption that often accompany coeliac disease: iron studies and ferritin, vitamin D, B12, folate, and bone health
Action: Continue eating gluten, obtain a gastroenterology referral for confirmation, and adopt a strict lifelong gluten-free diet only once the diagnosis is established.
When low
When negative (within range):
- A negative tTG-IgA in someone with normal total IgA makes coeliac disease unlikely
- If IgA is low (selective IgA deficiency), the negative result is unreliable: use deamidated gliadin IgG instead
- Persistent symptoms despite a valid negative result should prompt evaluation for other gastrointestinal conditions
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range