What You Should Know When You See Blood in Your Stool

Causes, Diagnosis, and Risk of Cancer with Rectal Bleeding

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Having blood in your stool can be terrifying, and your first worry may be that you have cancer.  What does it mean if you have rectal bleeding, and what are some of the causes?

Blood in Stool

You may note blood in the toilet, or on the tissue after wiping.  This blood can range through a multitude of different colors and be caused by many different conditions.  The important thing is not to panic, but not to ignore your symptoms.

When Is Blood in Stool an Emergency?

Most of the time if you have blood in your stool, you will have time to consider several questions and to schedule an appointment with your doctor.  If you have blood in your stool you should call 911 or go to the emergency room if:

  • You note large amounts of blood - either bright red blood or dark blood that looks more like coffee grounds.
  • You feel lightheaded or dizzy, or feel confused.
  • You feel your heart racing or you find it hard to catch your breath.
  • You experience any chest pain.
  • You have any symptoms that make you worry that your bleeding could be an emergency, even an intuitive feeling that you have something serious going on or a sense of impending doom.  Trust your instincts.

Color of Blood and Bleeding Location in the GI Tract

The color of the blood can give insight into where the bleeding is coming from and help make a diagnosis.

  • Bright red bleeding usually indicates bleeding from the rectum and the lower end of the colon (the "left side" of the colon.)
  • Bleeding in the upper colon (right side) and small intestine usually causes dark red, brown, or black bloody stools
  • Bleeding from the upper gastrointestinal tract such as the stomach and esophagus tends to cause dark, coffee ground appearing stools (melana.)

Is Blood In My Stools a Symptom of Cancer?

Most likely, the blood in your stool - something doctors call hematochezia - is related to a less serious condition.

However, if bleeding is cancer-related, colorectal cancer and anal cancer are two types of cancers that can cause rectal bleeding or blood to be present in the stool. It is important to note that precancerous conditions, like colon polyps, can cause rectal bleeding. BUT: Do not assume that because you have blood in your stool you have advanced cancer.

Blood in stools that is caused by cancer may be associated with other symptoms as well.  Some of these include fatigue, abdominal pain, pencil like thin stools, and unintentional weight loss - or a loss of over 5% of body weight over a 6 to 12 month period of time.

If It's Not Cancer, What Could Be Causing Blood in My Stools?

The most common causes of blood in stool are anal fissures or hemorrhoids.  Even if you are aware of hemorrhoids or a fissure, though, it's important to get checked out.  It's not uncommon for people to have more than one condition causing their bleeding, and the only way to know for sure is to be evaluated by your doctor.  Some non-cancerous causes of blood in stool include:

Stool Changes Caused by Foods and Medications

Medications or foods can also alter the color of stools. Bismuth subsalicylate (Pepto-Bismol) and Kaopectate can cause black stools following usage. Iron tablets and eating beets can also cause stool color changes that are not serious.

Seeing Your Doctor

It is important to see your doctor if you have blood in your stool. Do not assume that it is caused by hemorrhoids or anal fissures. While these are the most common culprit, you can't determine at home if it isn't polyps or another source that is the cause of the bleeding.  Colon cancer and rectal cancer are both most treatable in the earlier stages of the disease.


American Society of Colon and Rectal Surgeons. Colorectal Diseases and Treatments. Accessed 03/28/16. https://www.fascrs.org/colorectal-diseases-and-treatments

Qayed, E., Dagar, G., and R. Nanchal. Lower Gastrointestinal Hemorrhage. Critical Care Clinics. 2016. 32(2):241-54.

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