According to the ROC curve for faecal BAFF (Fig. 1A), the optimal cutoff value of 227.3 pg/ml was used to discriminate IBD form IBS, which showed a sensitivity of 84%, a specificity of 100%, a positive predictive value (PPV) of 100%, and a negative predictive value (NPV) of 64%. The gene discussed is TNFSF13B; the disease is irritable bowel syndrome.