Does Blood in Stool Mean Cancer?

Blood in your stool has many possible causes and most are not related to cancer. That’s why it’s important to know what might cause it and what to look for. Most of the time, blood in stool can be seen when you have a bowel movement (BM), but sometimes you can’t easily see it. It’s also important to tell your doctor right away if you see blood in your stool, as it can be a sign of a serious condition. 

What causes blood in stool?

Blood in your stool comes from problems that cause bleeding in the digestive system – or gastrointestinal system. There are several organs in your gastrointestinal (GI) system, including the esophagus, stomach, small intestine, colon, and rectum. Any of them can develop problems that might cause bleeding.

Possible causes of bleeding in the GI system include:

• Certain medicines – especially iron pills or supplements, blood thinners, including heparin, coumadin, aspirin, and nonsteroidal anti-inflammatory drugs (NSAIDs)
• Constipation – difficulty having bowel movements
• Hemorrhoids – veins in the anus or rectum that can become swollen from pushing or straining to have a bowel movement
• Infection of the stomach and intestines – sometimes called gastroenteritis
• Trauma or fissures – injury or small tears in the lining of the gastrointestinal tract
• Diverticulitis – swelling or inflammation of small pouches in the colon
• Stomach or peptic ulcer – a sore on the lining of the stomach
• Inflammatory bowel disease – such as Crohn's disease or ulcerative colitis
• Colon or rectal polyps – growths in the colon or rectum that may or may not turn into cancer
• Colon or rectal cancer – usually called colorectal cancer
• Anal cancer

What does blood in the stool look like?

Blood in the stool can look different depending on the cause of the bleeding, how much blood there is, and where the bleeding comes from in the GI tract or system. The color of the blood can help doctors know where the bleeding is.

Bright red blood in stool (hematochezia)

Smaller amounts of bright red blood in the stool means the bleeding is likely happening in the lower part of the GI tract. Sometimes this may only look like small amounts or streaks of bright red blood noticed on toilet paper after wiping. Some people might see small drops in or on their stool in the toilet. The most likely causes are hemorrhoids, polyps, tears or fissures, or certain inflammatory conditions. Sometimes there is rectal itching or discomfort along with bleeding.

Bright red blood in larger amounts is considered an emergency. This type of bleeding may discolor toilet water to be pink or reddish, and may stain undergarments.

Dark red blood in stool (melena)

Darker blood means the bleeding is usually coming from higher up in the GI tract. You may hear this called “internal bleeding” or “upper GI bleed.” Stools may be described as “tarry” because they look dark red, blackish or black. Blood clots may or may not be present or noticeable. Darker blood is most likely due to medicines (iron pills and blood thinners), an esophagus or stomach ulcer, inflammatory bowel disease, polyp, or cancer.

What does blood from a cancer look like in stool?

To the naked eye, blood in stool that’s from cancer can look like blood from other conditions or may be invisible. Simply looking at the amount and color of the blood – or stool – is not enough to know what’s causing the bleeding. The only way to determine what is causing blood in stool is to have a physical exam and possibly other tests. Besides a physical exam, common follow-up tests are:

• Stool tests to check the stool for blood and signs of colon cancer.
• Colonoscopy: an exam where a long tube is used to look at the inside structure of the colon and rectum for polyps, tumors or any other abnormal areas.
• Imaging tests to find abnormal areas where there might be bleeding
• Blood tests to check blood counts and organ function.

Because blood in the stool that’s coming from cancer can be invisible, regular colorectal cancer screening is important. Colorectal cancer screening tests look for signs of colorectal cancer, including hidden blood in the stool. Some tests, including stool-based tests, can be done in the privacy of your home. No matter the type of test, colorectal cancer screening helps to find cancers in earlier stages when treatment is more likely to be successful.

Should I be worried about blood in my stool?

There’s no way to tell what’s causing blood in your stool without getting checked by your doctor or other health care professional. Remember that blood in your stool is a warning from your body. It might be a mild, annoying problem that isn’t serious. But it could also be something more serious that needs medical attention.

How much blood in stool is too much? Is blood in stool an emergency?

Regardless of the cause, GI bleeding often starts and stops. This means you might see blood in your stool one day but not the next. Or it might happen every day but not with every stool.  The important thing to remember is to talk to your doctor if you see blood in your stool.