What this test measures
Tissue transglutaminase (tTG) is an enzyme in the gut wall that chemically modifies dietary gliadin (a wheat protein). In celiac disease — a genetically determined autoimmune response to gluten — the immune system makes IgA-class antibodies against this enzyme. Serum anti-tTG IgA is the single most sensitive and specific blood test for celiac disease in patients on a normal gluten-containing diet.
The assay is quantitative ELISA, reported in U/mL with assay-specific cut-offs. Sensitivity is 90–95% and specificity over 95% in untreated celiac disease. Modern paediatric guidelines (ESPGHAN 2020) allow biopsy-free diagnosis in children with tTG-IgA > 10× upper limit of normal plus a confirmatory anti-endomysial (EMA) antibody.
Why it matters
Celiac disease is now recognised as common in India — especially in wheat-eating regions of the north (Punjab, Haryana, Delhi, Uttar Pradesh) where prevalence reaches 1–2%. Many cases are silent or atypical, presenting as growth failure, iron-deficiency anemia not responding to iron, recurrent miscarriage, osteoporosis, infertility, or unexplained transaminitis rather than classic diarrhoea. The only treatment is lifelong strict gluten avoidance.
tTG-IgA is the first-line screening test. It must always be ordered alongside total IgA to detect IgA deficiency (which causes false-negative tTG-IgA). Positive tTG-IgA is confirmed by duodenal biopsy showing villous atrophy in adults; some children can be diagnosed by serology alone using current paediatric criteria.
How to prepare
Critical: do NOT start a gluten-free diet before the test. Antibodies fall and intestinal biopsy heals on gluten avoidance — leading to false-negative results and missed diagnosis. Continue eating normal wheat-containing food (at least one daily serving — a slice of bread, two chapatis, or equivalent) for at least 6 weeks before testing. No fasting required. Inform the lab if you have a known IgA deficiency — IgG-based tests are then used.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Anti-tTG IgA (U/mL)[1][2][3] | Negative — assay-specific (often < 7 U/mL or < 20 U/mL depending on platform) | Negative: low likelihood of celiac disease. Always confirm total IgA is normal. If symptomatic with low total IgA, switch to tTG-IgG or DGP-IgG. False negatives also occur on a gluten-free diet or in early disease. | Positive: highly suggestive of celiac disease. The higher the titer, the higher the probability. Confirm with duodenal biopsy showing villous atrophy (Marsh 3 lesion). Paediatric guidelines allow biopsy-free diagnosis if tTG-IgA > 10× upper limit of normal and EMA IgA also positive. |
Celiac disease test sequence
| Step | Test | Purpose |
|---|---|---|
| 1 | tTG-IgA + total IgA | First-line screen + check for IgA deficiency |
| 2 (if IgA deficient) | tTG-IgG or DGP-IgG | IgG-based alternative |
| 3 (if positive antibody) | Upper GI endoscopy + duodenal biopsy | Confirm villous atrophy (gold standard) |
| 4 (after diagnosis) | Strict gluten-free diet for life | Treatment |
| 5 (monitoring) | tTG-IgA at 6 and 12 months | Antibody should fall on gluten-free diet |
Frequently asked questions
Should I start a gluten-free diet before the test?
No — that is the most common and important mistake. Antibodies fall and biopsy heals on gluten avoidance, causing false-negative results. Continue normal wheat-containing food (at least one daily serving) for at least 6 weeks before testing.
Why is total IgA tested alongside tTG-IgA?
About 2–3% of celiac patients have selective IgA deficiency. They will not make tTG-IgA antibodies even with active disease, giving a false-negative result. Total IgA identifies these patients, who are then tested with IgG-based assays (tTG-IgG or DGP-IgG).
Do I still need a biopsy if tTG-IgA is positive?
In adults, yes — duodenal biopsy showing villous atrophy is the gold-standard confirmation before lifelong gluten avoidance. In children, modern paediatric guidelines (ESPGHAN 2020) allow biopsy-free diagnosis if tTG-IgA is > 10× upper limit of normal and a confirmatory EMA-IgA is positive.
How quickly does tTG-IgA fall on treatment?
On strict gluten-free diet, tTG-IgA usually halves within 3–6 months and normalises by 12–24 months. A persistently elevated tTG-IgA after a year strongly suggests ongoing gluten exposure (often hidden gluten in cross-contaminated food).
How common is celiac disease in India?
Once thought rare, it is now recognised as common in wheat-eating regions (1–2% prevalence in northern India). Most cases remain undiagnosed because of atypical or silent presentations — iron-deficiency anemia, infertility, osteoporosis, growth failure.
Can a low-positive tTG-IgA be a false positive?
Low-positive tTG-IgA (under 3× upper limit) is occasionally seen in other autoimmune diseases (type 1 diabetes, autoimmune thyroid disease, IBD), chronic liver disease, and some infections. Higher titers are more specific. A positive low-titer result needs biopsy confirmation.
Should family members be tested?
Yes. First-degree relatives of celiac patients have a 1 in 10 chance of also being affected. Asymptomatic first-degree relatives should be screened with tTG-IgA + total IgA (and HLA-DQ2/DQ8 if available).
Related Immunology tests
Tests commonly ordered alongside TISSUE TRANSGLUTAMINASE - IGA (TTG), or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Celiac Disease · accessed 2026-05-30T00:00:00.000Z
- ACG Clinical Guideline — Celiac Disease · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Celiac Disease Tests · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Tissue Transglutaminase IgA · accessed 2026-05-30T00:00:00.000Z
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