Testing for Celiac Disease (Gluten Sensitivity)
Order tissue transglutaminase IgA (TG2-IgA) antibody testing along with total IgA level as your initial screening tests for celiac disease. 1
Initial Serological Testing Algorithm
The diagnostic approach begins with serology, which is the crucial first step:
- TG2-IgA antibody: This is the primary screening test with 93.4% sensitivity and 95.8% specificity 2
- Total IgA level: Must be ordered simultaneously to identify IgA deficiency, which affects approximately 2-3% of celiac patients and causes false-negative IgA-based tests 1
If the patient is IgA deficient, switch to IgG-based testing:
- Order TG2-IgG or IgG deamidated gliadin peptide (DGP-IgG) antibodies 1
- Do NOT rely on TG2-IgG in patients with normal IgA levels, as it lacks specificity 1
Interpretation and Next Steps Based on Results
High-Positive TG2-IgA (>10× upper normal limit)
When TG2-IgA is strongly positive at levels exceeding 10 times the upper limit of normal:
- In children: Diagnosis can be established without biopsy if confirmed with positive endomysial antibodies (EMA) in a second blood sample, achieving virtually 100% positive predictive value 1
- In adults: The 2025 ESsCD guidelines now conditionally support a no-biopsy approach for selected adults with high-titre serology (≥10× ULN) using validated high-performance ELISAs 3, though esophagogastroduodenoscopy (EGD) with duodenal biopsies may still be performed for differential diagnosis 1
Low-Positive or Equivocal TG2-IgA
- Proceed to upper endoscopy with duodenal biopsies (at least 4 samples from the second part of duodenum) 3
- Histological analysis should include Marsh classification and lymphocyte counting 1
Negative Serology with Strong Clinical Suspicion
- Still perform duodenal biopsies if clinical suspicion remains high 1
- If biopsies show villous atrophy but serology is negative, consider HLA-DQ2/DQ8 testing to help clarify diagnosis 1, 4
Critical Pitfalls to Avoid
Do not test patients already on a gluten-free diet: Gluten avoidance reduces sensitivity of both serology and biopsy 1, 5. If the patient has already eliminated gluten, they must resume eating gluten (three slices of wheat bread daily) for 1-3 months before testing 1.
Do not order IgG tests routinely: IgG-based celiac testing (TG2-IgG, DGP-IgG) should only be used in confirmed IgA deficiency 1, 6. Using IgG tests in IgA-sufficient patients leads to false positives.
Do not skip the total IgA level: Ordering TG2-IgA without checking total IgA is a common error that misses IgA-deficient celiac patients who will test falsely negative 1.
Role of Additional Testing
HLA-DQ2/DQ8 genetic testing has limited diagnostic utility but high negative predictive value 1, 4. Use it to:
- Rule out celiac disease in seronegative patients with histologic changes
- Evaluate patients without prior serologic confirmation at diagnosis
- Screen high-risk asymptomatic individuals (first-degree relatives, patients with autoimmune diseases) 6, 5
Endomysial antibody (EMA) testing is no longer routinely recommended for confirmation according to the 2025 ESsCD guidelines, as modern high-performance TG2-IgA ELISAs are sufficiently accurate 3. However, it may still be used in specific scenarios requiring additional confirmation, particularly in pediatric no-biopsy diagnoses 1.