ttg iga test
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The first-line blood test for celiac disease — it measures the immune system's autoantibodies against the body's own tTG enzyme.
The TTG IgA test (also written TG2 IgA or anti-tTG IgA) measures the level of IgA-class antibodies against tissue-transglutaminase (tTG) in blood serum. It is the recommended first-line serological test for celiac disease in most international guidelines, because of its combination of high accuracy, low cost, and wide availability.
Performance
| Metric | Value |
|---|---|
| Sensitivity | 92.8% |
| Specificity | 97.9% |
| Cost | Low |
| Availability | Widely available |
- 92.8% sensitivity means it correctly identifies ~93 in 100 true celiac patients
- 97.9% specificity means ~98 in 100 positive results are true celiac (low false positive rate)
- The remaining ~7% of celiac patients missed are often those with mild intestinal damage (low antibody levels) or IgA deficiency
What It Actually Measures
When tissue-transglutaminase cross-links to gliadin (transamidation), it creates novel protein complexes that the immune system attacks. Anti-tTG antibodies are the by-product of this attack — they circulate in blood and can be measured. Their level broadly correlates with the degree of intestinal damage: higher antibody levels = more active disease = more severe villous-atrophy.
Critical Pre-Test Requirement
The patient must be actively consuming gluten for the test to be accurate. Antibody levels fall within weeks-to-months of starting a gluten-free-diet. Patients already on GFD must undergo a gluten-challenge before meaningful testing.
When to Order Alongside
Because IgA deficiency invalidates the TTG IgA test, guidelines recommend always testing total IgA levels simultaneously. If IgA is deficient, order DGP IgG or TTG IgG instead.
Role in Monitoring
TTG IgA is also used during follow-up. Rising levels on a supposedly strict GFD suggest inadvertent gluten exposure. However, a negative or low TTG IgA does not guarantee perfect intestinal healing — some patients have mucosal damage without detectable antibodies.
ESPGHAN Paediatric Threshold
In children, ESPGHAN (2020) guidelines allow biopsy to be skipped if TTG IgA is ≥10× the upper limit of normal + EMA positive + symptoms present. This "no-biopsy" pathway reduces invasive procedures in highly probable cases.
Related Concepts
celiac-serology | tissue-transglutaminase | autoantibodies-celiac | iga-and-iga-deficiency | gluten-challenge | marsh-classification | endoscopy-biopsy | gluten-free-diet
Referenced In
diagnosis | management | overview | glossary