tTG-IgA Test for Celiac Disease: Interpretation, Diagnostic Pathway, and Monitoring

The tissue transglutaminase IgA (tTG-IgA) assay is the single best serologic test for celiac disease in patients consuming gluten. Sensitivity 93–98%, specificity 96–98% (vs. Marsh ≥2 histology).

Test Principles

• tTG (enzyme cross-linking gluten peptides) is the autoantigen.
• IgA class measured; parallel total IgA rules out selective IgA deficiency (2–3% of CD patients).

Interpretation Framework

tTG-IgA Result	Total IgA	Next Step
Negative (	Normal	CD unlikely; if high suspicion, consider HLA-DQ2/DQ8 or EMA-IgA.
Weak positive (1–3× ULN)	Normal	ESPGHAN: if >10× ULN + EMA+ + symptoms + HLA+, biopsy may be omitted in children. Adults: proceed to endoscopy.
Strong positive (>10× ULN)	Normal	High PPV; pediatric no-biopsy pathway per ESPGHAN 2020. Adults: confirm with biopsy.
Any positive	Low/absent	False-negative risk. Order tTG-IgG / DGP-IgG / EMA-IgG; proceed to biopsy.

Pre-Test Requirements

• Patient must be on gluten-containing diet (≥1 slice bread/day × 6–8 weeks).
• Antihistamines, PPIs, steroids do not affect serology.

Confirmatory Testing

• Endoscopy with duodenal biopsies: ≥4 from D2, 1–2 from bulb. Marsh-Oberhuber classification.
• HLA-DQ2/DQ8: Negative predictive value >99%; useful if serology discordant or GFD already started.

False Positives / Differential

• Autoimmune liver disease (AIH, PBC), type 1 diabetes, Down syndrome, Turner syndrome, chronic liver disease, HIV — may have low-titer positivity without villous atrophy.
• Crohn's disease, tropical sprue, giardiasis, SIBO, olmesartan enteropathy — histologic mimics.

Monitoring on GFD

tTG-IgA normalizes in 6–12 months (median 80% drop by 6 months). Persistent elevation → inadvertent gluten exposure (dietitian review) or refractory disease.

tTG-IgA is the cornerstone of CD diagnosis; interpretation requires clinical context, total IgA, and histologic correlation.