How to tell if theres blood in your stool

Stories and expert health tips from Sunnybrook

Table of Contents Show

About the author
Conditions that may cause rectal bleeding
Symptoms that may accompany rectal bleeding
Rectal bleeding and cancer
Why the color of the blood matters
Rectal bleeding in young people

Q: I saw a Colorectal Cancer Awareness poster that said to look out for blood in my stools. What exactly am I looking for?

A: A person’s stool (poop) is a window into their health and a precious warning sign of a problem, so look at it before you flush it. Keeping an eye on your stools is an important step in being aware of colorectal cancer and identifying early signs of the disease.

The topic of what one’s stool says about their health is very extensive and I won’t get into it all here, but let’s talk about seeing blood.

Firstly, blood in your poop is not normal. All blood passed in the stool, around the stool or after the stool is abnormal and represents a problem of varying severity.

So to answer the question, you are just looking for blood. And if you see it, you need to report it to your family physician for investigation. It’s just that simple. Having said that, there are certainly more worrisome characteristics of the blood in one’s stool and certain features that you should be aware of in order to report them to your physician. To understand these characteristics, one must imagine where this blood is coming from.

Colorectal cancer is a disease of the cells of the inner lining of the colon or rectum. The cells begin to grow out of control, first forming a cluster of cells called a polyp and eventually becoming a cancer as the cells burrow deeper into the wall. Because these polyps and eventual cancers are growing on the inner lining of the bowel, they ooze or bleed into the bowel and that blood then becomes incorporated with the stool as it passes through.

With that background, one can begin to imagine just how blood in the stool might look if it is coming from a colorectal cancer. If the cancer is in the right side of the colon (the beginning of the colon and furthest from the anus) then the blood might be undetectable by the eye by the time it reaches the toilet. If there is lots of blood coming from a cancer in the right colon, it may no longer look like red blood by the time it reaches the toilet but rather like black tar mixed in with the stool.

If the cancer is further along in the colon or even in the rectum, the blood will still be red smeared along the stool as it hits the toilet or the blood will be mixed in with the stool but still bright red in appearance.

Finally, if the cancer that is bleeding is in the rectum, just before the exit, you might see only blood coming into the toilet either prior to or after the stool as it is bleeding directly out of the anus rather than mixing with stool.

So by understanding how blood in the stool could be a warning sign of a cancer, it also becomes clearer why we use a fecal immunochemical test (FIT) to look at the stool microscopically (and why it’s so important!) This test checks for occult (hidden) blood in the stool as a screening test for colorectal cancer — it can find blood that isn’t visible to the eye when you look in the toilet.

The test isn’t specific — many other things can lead to hidden blood in the stool and the test can’t tell which it is causing the blood. But it is very sensitive, which means that almost all colorectal cancer patients would be positive if the test was done. That means very few false negatives, which is ideal for a screening test.

It is obviously very important to understand that many different colorectal problems can lead to blood in the stools, not just cancer. But do remember that regardless of the cause, blood in your poop it is not normal and needs discussion and investigation by your primary care physician. The characteristics of the blood will offer clues but by no means will it make a diagnosis and almost certainly the next step will be a colonoscopy to definitively sort out what’s going on.

In very simple terms, please do this for me: Turn and look at your stool before flushing. It could save your life.

(This post was updated in August 2020 to reflect a change in Ontario’s colorectal screening test from the fecal occult blood test to the FIT)

About the author

Dr. Ashamalla is a colorectal cancer surgeon at Sunnybrook’s Odette Cancer Centre specializing in minimally invasive surgical treatments. He’s also a teacher and researcher in surgical education and simulation, and he's a consultant surgeon to the Toronto Maple Leafs. Read more posts on his blog.

It can be unsettling to find signs of blood in your stool. But you shouldn’t immediately think the worst. True, blood in the stool may be caused by a variety of conditions or diseases, including cancer, that could develop into serious health issues if left untreated. But the blood may also be a product of more benign conditions, such as hemorrhoids, which, while still unwanted, are often less serious than other conditions.

Still, if you notice blood after a bowel movement, it’s a good idea to contact your doctor to find the cause, says Toufic Kachaamy, MD, Gastroenterologist and Interventional Program Specialist at Cancer Treatment Centers of America® (CTCA), Phoenix.

“Blood in the stool is always abnormal and needs to be investigated,” he says. “Never assume it’s benign or not significant until you’ve had a thorough investigation by your physician.”

In this article, we’ll explore the causes of rectal bleeding and bloody stools and what you should do about them. Topics include:

Conditions that may cause blood in the stool
Symptoms that may accompany rectal bleeding
Rectal bleeding and cancer
Why the color of the blood matters
Rectal bleeding in young adults

If you’ve been diagnosed with cancer of the digestive system, including colorectal cancer, stomach cancer or esophageal cancer, and are interested in a second opinion on your diagnosis and treatment plan, call us or chat online with a member of our team.

Conditions that may cause rectal bleeding

Your poop is made up of about 75 percent water, but it also contains an amalgam of undigested bits of food, mucus, dead cells and bacteria.

What shouldn’t be in your poop? Blood.

Many conditions, including cancer, that cause blood to appear in your stool may become serious if not addressed early. Some are related to auto-immune conditions, caused when an overactive immune system attacks healthy cells in the body. Others develop over time, perhaps due to diet or lifestyle, and may cause only minor pain or discomfort.

Conditions, other than cancer, that may cause blood in stool include:

Anal fissures: Small tears in the lining of the anus may be caused by constipation, difficult bowel movements or sexual activity.

Crohn’s disease or colitis: These auto-immune conditions may cause inflammation of the digestive system, leading to diarrhea and abdominal pain.

Diarrhea: Runny stools caused by illness, contaminated food or overindulgences may result in a sore or inflamed anus and blood streaks that appear on toilet paper after multiple bathroom trips.

Food poisoning: Tainted food may lead to infections that cause severe digestive distress.

Diverticulosis: Pouches in the lining of the colon, called diverticula, may become inflamed or infected.

Hemorrhoids: Swollen blood vessels in the rectum or on the anus may develop due to constipation or frequent sitting.

Ulcers: Open sores in the lining of the stomach or bowels are often caused by a bacterial infection.

Some of these conditions may heal or resolve themselves within a few days. But if they produce blood in the stool at any time, you should still tell your doctor, Dr. Kachaamy says.

“Sometimes blood in the stool can be caused by benign conditions such as hemorrhoids, a small fissure after constipation or an infection and can resolve on its own,” he says. “However, bleeding from cancer or inflammatory bowel disease can also be intermittent, and so any bleeding needs to be investigated.”

Symptoms that may accompany rectal bleeding

In addition to bleeding, other symptoms may develop from some of these conditions. It’s important to tell your doctor about all the symptoms you’ve been experiencing and any family or personal history that may be related to your condition.

Other symptoms may include:

Itching or burning in the anus
Diarrhea or constipation
Nausea or vomiting
Cramps
Bloating
Pain
Fever

Rectal bleeding and cancer

Blood in the stool often is a sign of bleeding in some area of the digestive tract, from the esophagus to the anus. And while bleeding may occur for a number of reasons, including the conditions listed above, it’s important to either rule out cancer or catch it when signs appear.

Cancer develops when mutated or damaged cells grow out of control. In many cases, the damage has affected the systems in the cells that regulate their growth and division. Cancers in the digestive system often develop in the soft lining of the esophagus, stomach, bowels or rectum and typically cause inflammation and bleeding.

Why the color of the blood matters

The color of the blood and the texture of the bloody stool may be influenced by many factors, especially what you’ve eaten. Beets can produce stool that turns the toilet water red or purple, while green, leafy vegetables rich in chlorophyl may produce darker stools.

If the bloody stool was caused by diseases such as cancer, the color may indicate where the bleeding is coming from in the digestive tract and may help doctors find its source.

For instance:

Bright red blood in stool often means the blood is fresh and the bleeding is lower in the colon or rectum. This condition is called hematochezia.
Dark red blood may mean the bleeding is higher in the colon or in the small intestine.
Dark, tar-like stool may mean the bleeding is in the stomach or the gastroesophageal junction—where the stomach meets the esophagus. This condition is called melena.

Polyps, which are small growths in the lining of the colon, may also grow and begin to bleed. Polyps may be benign at first, but they may develop into cancer. That’s why it’s important to talk to your doctor about when to get a colonoscopy, which is considered the gold standard for detecting colorectal cancer early. Polyps found during the procedure may be removed during the colonoscopy.

Rectal bleeding in young people

While cancer is most commonly diagnosed in older adults, young adults often develop conditions that may cause rectal bleeding. Irritable bowel diseases such as ulcerative colitis or Crohn’s disease often first begin affecting adults in their 20s or 30. These conditions may increase the risk of colorectal cancer later in life.

Also, new diagnoses of colorectal cancer are surging in young adults. The disease is now the leading cause of cancer deaths in people 20 to 45 years old. Dr. Kachaamy says young adults should not ignore blood in the stool, even if it goes away after a few days.

“While some conditions that cause bleeding resolve themselves quickly without treatment, other conditions like cancer and inflammatory disease will need treatment. Identifying them early offers you a stronger change for a better outcome,” he says. “Colorectal cancer—especially rectal cancer—is on the rise in young adults, and we currently do not screen average-risk adults below the age of 45. This means that to diagnose these diseases early, you need to be vigilant to early symptoms such as bleeding and not neglect these symptoms.”