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

Background 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. Objectives This study compares 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. Methods We conducted a multicenter prospective quasi-experimental clinical study. Two subsets of individuals were considered: 1) 20 patients with CD and 15 non-CD controls previously diagnosed, to evaluate the first aim; 2) 45 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). Results 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 45 subjects. Conclusion The percentage of TCRγδ⁺ IELs and the gut-homing CD8⁺ T-cell assay are promising diagnostic methods for CD on a GFD. Notably, the CD8+ T-cell assay provides a consistent and reliable alternative to the extended GC, eliminating the need for the invasive procedures to obtain duodenal samples and the prolonged gluten ingestion.