Blood in stoll. what are the reason. what should i notice. i have constipation issue since long time.?

CANCER: Please see your primary care physician. Blood in the stool has many causes the most severe being cancer or tumor formation. Seeing as you are also constipated there is a chance that your bowel (intestine) is obstructed.

See a doctor.: Most likely it's due to hemorrhoids (inflammation of the veins around the anus), but if you're over the age of 50, or have a family history of colon cancer, seeing a doctor is an absolute must. They will likely do a rectal exam and possibly refer you for a colonoscopy.