A real‐world comparison of celiac tissue transglutaminase immunoglobulin A antibody levels in pediatric patients using two different diagnostic kits

Objectives Pediatric celiac disease (CeD) may be diagnosed without a biopsy when tissue‐transglutaminase (TTG) immunoglobulin A (IgA) antibodies are ≥10x the upper limit of normal (ULN) and anti‐endomysial antibodies are positive in a second sample. The no‐biopsy diagnosis demands a very high accuracy and reliability of the TTG diagnostic kits. Inter‐assay differences may affect category classification. We compared TTG‐IgA levels performed by two reliable kits: Bioplex 2200 and Liaison‐XL in routine care. Methods Using the Clalit Health Services database, we identified pediatric patients with paired TTG‐IgA measurements from both kits within ≤14 days. Values were expressed as multiples of ULN and categorized: <ULN, 1–3x ULN, 3–10x ULN, and >10x ULN. Agreement was assessed for ≤7 and ≤14‐day windows using Cohen's ĸ . Results Category discordance occurred in 17.4% (109/625) of paired tests within 14 days and 11.8% (38/321) within 7 days. Overall agreement was substantial ( ĸ = 0.62 for 14 days; ĸ = 0.63 for 7 days). Concordance was high for negative results (96.0%), but significantly lower for the critical >10x ULN threshold at 14 days (88.2%, p = 0.009). Conclusions Significant discordance between these two reliable TTG‐IgA kits at 14 days, exceeding 10% in the >10x ULN category, warrants careful consideration when using the no‐biopsy approach for CeD diagnosis, as assay choice may impact clinical classification.