Described herein are methods and systems for detecting and/or distinguishing irritable bowel syndrome (IBS) from inflammatory bowel disease (IBD) and celiac disease. The methods and systems can utilize the detection of anti-CdtB antibodies and/or anti-vinculin antibodies to detect IBS, distinguish IBS from IBD and/or celiac disease. Further described are methods for selecting a therapy to treat IBS, IBD or celiac disease.