Are tTG and gliadin alternative names for the same test?

No, tTG and gliadin are NOT the same test—they are distinct serological markers for celiac disease screening.

tTG (tissue transglutaminase antibodies) and gliadin antibodies test for different antigens and have markedly different diagnostic performance. Understanding this distinction is critical for accurate celiac disease diagnosis.

Key Differences Between the Tests

tTG (Tissue Transglutaminase Antibodies)

• Primary screening test for celiac disease 1
• Tests for IgA antibodies against tissue transglutaminase (the major autoantigen in celiac disease)
• Superior diagnostic accuracy: sensitivity 90.7-97.7% and specificity 70.2-87.4% 2
• First-line recommended test by guidelines 1, 3

Gliadin Antibodies (Traditional AGA)

• Tests for antibodies against gliadin (a component of gluten)
• Significantly inferior performance: The antigliadin antibody is less specific than tTG and is NOT recommended for screening 1
• Largely abandoned in modern practice due to poor accuracy 4

Deamidated Gliadin Peptide (DGP) Antibodies

• Newer generation gliadin-based test using modified peptides
• Better performance than traditional gliadin antibodies but still inferior to tTG 5
• Sensitivity 96.4% but specificity only 77.4-95.4% 2
• Not recommended as initial screening 6
• May have limited role as confirmatory test in specific scenarios 7, 8

Clinical Algorithm for Celiac Disease Screening

Step 1: Initial Screening

• Order IgA tTG as first-line test 1, 3
• Simultaneously check total IgA level to detect IgA deficiency (present in 1-3% of celiac patients) 1

Step 2: If IgA Deficient

• Use IgG-based tests: IgG tTG or IgG DGP 1, 3
• Do NOT use IgA-based tests (will be falsely negative)

Step 3: Confirmatory Testing

• If tTG positive: Consider endomysial antibody (EMA) for confirmation (higher specificity 93.8-99.6%) 1, 2
• Proceed to duodenal biopsy for definitive diagnosis 1, 9

Critical Pitfalls to Avoid

Do NOT order traditional antigliadin antibodies (AGA) for celiac screening—guidelines explicitly state this test is not recommended due to poor specificity 1. This is outdated testing.

Do NOT use DGP as initial screening in IgA-sufficient patients. When DGP is positive but tTG is normal, the positive predictive value is only 2.5% 6. This leads to unnecessary endoscopies.

Do NOT forget to check total IgA levels when ordering IgA tTG—missing IgA deficiency will result in false-negative results and missed diagnoses 1.

When DGP May Have Limited Utility

DGP testing may be considered in:

• IgA-deficient patients (use IgG DGP) 3, 10
• Children under age 2 (requires further research) 6
• Potential confirmatory role when combined with very high tTG levels (≥10x upper limit of normal) in no-biopsy diagnostic approaches 7, 8

However, even in these scenarios, tTG remains the superior primary test 5, 11.