Celiac Disease Blood Test: tTG-IgA and What Your Results Mean
Celiac disease is a common autoimmune condition — affecting roughly 1 in 100 people worldwide — in which gluten triggers immune damage to the small intestine. Blood tests are the standard first-line investigation, with the tTG-IgA test being the most accurate and widely used. Yet interpretation is nuanced: you must be eating gluten at the time of testing, total IgA must be checked simultaneously, and a positive result still requires intestinal biopsy confirmation in most cases.
Upload your blood test PDF to see how your metabolic, liver, and inflammatory markers look on Clariti.
Get My Score →Why Blood Tests Are the First Step for Celiac
Before celiac disease could be diagnosed by blood test, the only path to diagnosis was intestinal biopsy — an endoscopic procedure requiring sedation. The development of reliable serological (blood-based) markers in the 1990s transformed celiac diagnosis, allowing non-invasive screening of high-risk individuals and the general population.
Blood tests detect antibodies that the immune system produces in response to gluten exposure. In celiac disease, gluten triggers the production of antibodies against both an intestinal enzyme (tissue transglutaminase) and gluten proteins themselves (deamidated gliadin). These antibodies are detectable in blood and fall to undetectable levels when gluten is removed from the diet.
The Celiac Blood Test Panel
| Test | Sensitivity | Specificity | When Used |
|---|---|---|---|
| tTG-IgA (anti-tissue transglutaminase) | 93–98% | 94–97% | First-line test for all patients ≥2 years |
| Total IgA | — | — | Always ordered alongside tTG-IgA to rule out IgA deficiency |
| DGP-IgG (deamidated gliadin peptide) | 80–90% | 90–95% | Used when patient has IgA deficiency |
| DGP-IgA | 85–95% | 90–95% | Children under 2 years (tTG less reliable) |
| EMA-IgA (endomysial antibody) | 90–95% | 99% | Confirmatory test — very specific but expensive |
| tTG-IgG | 70–80% | 90% | IgA-deficient patients; less reliable than DGP-IgG |
Understanding tTG-IgA: The Primary Test
Tissue transglutaminase (tTG) is an enzyme found in the intestinal lining. In celiac disease, the immune system mistakenly attacks tTG — treating it as a foreign protein — and produces IgA antibodies against it. The tTG-IgA test measures these antibodies. The higher the level, the more likely celiac disease is present and the more severe the intestinal damage tends to be.
Results are reported as a number with a reference range (typically negative: <4–7 U/mL, depending on the laboratory). A result more than 10 times the upper limit of normal (often called "strongly positive" or "≥10× ULN") has been found in studies to be so specific for celiac disease that some guidelines now consider it sufficient to diagnose without biopsy in the right clinical context — particularly in children.
Total IgA: Why It Must Be Checked
IgA deficiency affects roughly 1 in 500 people in the general population — but is 10–15 times more common in people with celiac disease. If a patient is IgA-deficient, the tTG-IgA test will return a falsely negative result even in the presence of celiac disease, because there are no IgA antibodies to detect.
This is why total serum IgA must always be checked at the same time as tTG-IgA. If total IgA is low (<0.2 g/L in adults), IgA-based tests are unreliable and the patient should instead be tested with IgG-based antibodies — specifically DGP-IgG or tTG-IgG. Failing to check total IgA is a common diagnostic error.
Why Active Gluten Consumption Is Required for Accurate Testing
This is the most important thing to understand about celiac blood tests: they are only valid if the patient has been eating a normal gluten-containing diet for at least 6–8 weeks before the test. Antibodies fall rapidly when gluten is eliminated — within days to weeks. Someone who has already started a gluten-free diet before testing may return negative results even with active celiac disease.
If you have already started a gluten-free diet and want to be tested, you would need to do a "gluten challenge" — deliberately reintroducing gluten for 6–8 weeks before testing. This should be done under medical supervision, as it can cause significant symptoms in someone with established celiac disease. Genetic testing (HLA-DQ2/DQ8) is an alternative that can rule out celiac without a gluten challenge.
What Comes After a Positive Blood Test
A positive tTG-IgA generally leads to a referral for upper gastrointestinal endoscopy with duodenal biopsy. The biopsy assesses the degree of villous atrophy (flattening of the intestinal lining) using the Marsh classification. Confirming the diagnosis histologically (Grade Marsh 3) remains the gold standard in adults before committing to a lifelong gluten-free diet.
In children, guidelines from ESPGHAN (the European Society for Paediatric Gastroenterology) allow diagnosis without biopsy if tTG-IgA is ≥10× ULN, EMA is positive on a separate blood draw, and the child has symptoms — this "no-biopsy pathway" is not yet standard in all countries for adults.
Non-Celiac Gluten Sensitivity
Many people experience symptoms when eating gluten — bloating, brain fog, fatigue, gut pain — but have negative celiac antibodies and normal intestinal biopsy. This is called non-coeliac gluten sensitivity (NCGS). There is no diagnostic blood test for NCGS; it is diagnosed by exclusion (negative celiac tests, negative wheat allergy, symptom improvement on gluten-free diet, and symptom recurrence on gluten reintroduction).
NCGS is real and affects a meaningful proportion of people — though the exact mechanism is debated and for some patients the trigger may be fructans (a FODMAP in wheat) rather than gluten itself. The important thing is to rule out celiac disease first with appropriate testing before concluding NCGS, since celiac has serious long-term health consequences if undiagnosed and untreated.
See how your blood tests score
Upload your blood test PDF — free, private, no account needed. Get an A–F grade across 6 health domains in seconds.
Analyze My Blood Test →Medical Disclaimer
This article is for educational purposes only and does not constitute medical advice. Reference ranges, supplement dosages, and nutritional information mentioned are general educational guidance from published research — not personalised recommendations. Do not use this content to self-diagnose or self-treat any condition. Always consult a qualified healthcare provider before making any changes to your health regimen, medications, or supplements.
