The sensitivity and specificity of the decision tree model of IgA to differentiate IBS subgroups and HCs were 45.54% (46/101) and 80.92% (106/131) for IBS patients with persistent symptoms, 29.55% (13/44) and 93.13% (122/131) for IBS patients with severe abdominal pain/discomfort, 32.81% (21/64) and 88.55% (116/131) for IBS patients with severe symptoms, 30.65% (19/62) and 89.31% (117/131) for IBS patients with severe anxiety. This evidence concerns the gene CD79A and irritable bowel syndrome.