Celiac Disease Diagnosis: Serology, Biopsy, and Gluten-Free Management

Serologic Testing: The First Step

Tissue transglutaminase IgA (tTG-IgA) is the recommended initial screening test, with sensitivity of 93-98% and specificity of 95-98% in adults on a gluten-containing diet. Total serum IgA should be measured concurrently, as IgA deficiency (present in 2-3% of celiac patients versus 0.2% of the general population) produces false-negative tTG-IgA results. In IgA-deficient patients, deamidated gliadin peptide IgG (DGP-IgG) or tTG-IgG should be substituted. Endomysial antibody (EMA-IgA) serves as a confirmatory test with near-100% specificity but lower sensitivity (approximately 90%) and higher cost.

Duodenal Biopsy: Still the Gold Standard

The 2023 ACG Clinical Guideline recommends esophagogastroduodenoscopy with at least 4 biopsies from the second portion of the duodenum and 2 from the duodenal bulb for all adults with positive serology. Marsh classification grades histologic severity: Marsh 1 (increased intraepithelial lymphocytes above 25/100 enterocytes), Marsh 2 (crypt hyperplasia), and Marsh 3a-c (partial to total villous atrophy). Notably, patchy mucosal involvement occurs in up to 20% of cases, making multiple biopsies essential to avoid sampling error.

Serology-Only Diagnosis: Pediatric Model, Adult Potential

The 2020 ESPGHAN guidelines allow biopsy-free diagnosis in children when tTG-IgA exceeds 10 times the upper limit of normal with positive EMA on a separate blood sample. The ProCeDE study validated this approach in 707 children with 99.75% positive predictive value. In adults, the multinational CREST trial and several retrospective analyses suggest that tTG-IgA above 10x ULN with positive EMA predicts Marsh 3 histology in over 95% of cases. However, current ACG guidelines still recommend confirmatory biopsy in adults pending further prospective data.