It is possible, but less likely, that the
sigmoidoscopy itself can cause the blood in the stool. If you continue to have an incomplete evalcuation (tenesmus), you may want to consider obtaining a full colonoscopy, which a more comprehensive evaluation of the colon. Possible causes would include diverticulosis, inflammatory bowel disease, or a polyp/mass that is out of range of the flexible sigmoidoscope.
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.
Thanks,
Kevin, M.D.