Diagnosis of celiac disease on a gluten-free diet: a multicenter prospective quasi-experimental clinical study

Diagnosing celiac disease (CD) in individuals adhering to a gluten-free diet (GFD) presents significant challenges. Current guidelines recommend a gluten challenge (GC) lasting at least 6-8 weeks, which has several limitations. Our aim was to compare four approaches previously proposed for diagnosing CD on a GFD: IL-2 serum levels, gut-homing CD8⁺ T cells, % TCRγδ⁺ intraepithelial lymphocytes (IELs), and UBE2L3 gene expression. Additionally, we evaluated the CD8⁺ T-cell-based method with a 3-day GC against the standard GC protocol.

We conducted a multicenter prospective quasi-experimental clinical study. Two subsets of individuals were considered: (1) 20 patients with CD previously diagnosed and 15 non-CD controls, to evaluate the first aim; (2) 41 individuals with uncertain diagnosis who were on a GFD and required GC following current clinical guidelines, to assess the second aim. All participants underwent a 3-day GC (10 g gluten/day).

Among CD patients and non-CD controls, the sensitivity and specificity of IL-2, gut-homing CD8⁺ T cells, and UBE2L3 were 82.4% and 83.3%, 88.2% and 100%, and 52.9% and 100%, respectively. The percentage of TCRγδ⁺ IELs showed 88.2% sensitivity. In the uncertain diagnosis group, a CD8⁺ T-cell positive response was observed in 8 of the 41 subjects.

The percentage of TCRγδ⁺ IELs and the analysis of IL-2 levels and gut-homing CD8⁺ T cells are promising diagnostic methods for CD on a GFD. Notably, our results suggest that the CD8⁺ T-cell assay may provide a consistent and reliable alternative to the extended GC, eliminating the need for invasive procedures to obtain duodenal samples and prolonged gluten ingestion. However, further research with larger cohorts are necessary to validate these findings and establish their definitive clinical utility.