As mentioned previously, IBS is a diagnosis of exclusion. That being said, the workup for liver and gallbladder disease is pretty good with hepatitis being ruled out, non-revealing liver function tests, and normal abdominal ultrasound.
A normal ultrasound would make cholecystitis unlikely. If you wish to pursue more tests, a HIDA scan can be done to further evaluate for this disease.
If the liver and gallbladder are normal, you can consider a colonoscopy to evaluate for colitis or inflammatory bowel disease. Each of these disorders can discolor the stool as well.
You can discuss these options with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
http://www.straightfromthedoc.com
Maybe there are coexisting infections???