How is irritable bowel syndrome diagnosed?

Irritable bowel synd. Irritable bowel syndrome (IBS) is relatively benign compared to inflammatory bowel disease (IBD). IBS is diagnosed clinically based upon Rome or Manning criteria (http://www.mayoclinic.org/diseases-conditions/irritable-bowel-syndrome/basics/tests-diagnosis/con-20024578). Depending upon age & other risk factors, some invasive testing eg colonoscopy may be performed but often diagnosis made clinical.