Chances are you’ve heard of colonoscopies before. Maybe a family member recently had one to screen for cancer. Perhaps you’re wondering when colonoscopies are recommended and why. Or maybe a colonoscopy is in your future, and you’re wondering what it might find.

Read on to learn why your doctor may recommend a colonoscopy and how it’s used to identify colon cancer and gastrointestinal problems.

Reasons for a colonoscopy test: Why your doctor might recommend one

There are four main reasons why a doctor may recommend a colonoscopy: cancer prevention, diagnosis of gastrointestinal symptoms, follow-up and to check if you’re ready for surgery.

Preventive screening for colorectal cancer

A screening colonoscopy is the most common way to test for colorectal cancer in people without any symptoms. Screening is typically recommended for everyone starting at age 45 – but your doctor may recommend you get screened sooner if you have certain risk factors like hereditary colorectal cancer syndromes.

Screenings are important because they can help doctors identify colon or rectal cancer early, when it’s easier to treat. Plus, these types of preventive health screenings are usually 100% covered by insurance, even if you haven’t met your deductible. But it’s always a good idea to check with your insurance provider to see how cancer screenings are covered by your insurance plan.

Also, it’s important to know that diagnostic colonoscopies to explore the potential cause of gastrointestinal symptoms or an issue like anemia are not considered screenings. So, insurance coverage and cost sharing are usually different. We’ll talk more about diagnostic colonoscopies in the next section.

Exploring possible causes of gastrointestinal symptoms

Doctors may recommend a diagnostic colonoscopy if you are experiencing gastrointestinal symptoms that could be related to colorectal cancer or a digestive disorder. These symptoms may include:

  • Abdominal pain, gas or bloating
  • Changes in how often you have a bowel movement
  • Poop that’s consistently not a normal stool color or has an unusual appearance
  • Recurrent diarrhea
  • Recurrent constipation
  • Blood in the toilet, on the toilet tissue or in your poop
  • Frequent indigestion
  • Unexplained weight loss
  • Malnutrition
  • Chronic fatigue

Usually, a colonoscopy is just one step in identifying the cause of gastrointestinal symptoms. Other tests can include blood and stool tests, ultrasounds or X-rays.

If your doctor recommends a colonoscopy, it’s because they want to look at the inside of your colon for visual signs of what could be causing your symptoms. During the procedure, they’ll also be able to take a tissue sample – which is called a colon biopsy – if needed.

Following up on previous colon cancer tests or procedures

If you’ve had colon polyps or abnormal tissues identified by a previous colonoscopy, a follow-up colonoscopy may be recommended to look for or remove more polyps. Or if an at-home FIT test for colorectal cancer screening came back positive, a colonoscopy would be the recommended next step.

Ensuring you’re ready for surgery

A colonoscopy may be used to see if you’re healthy enough for certain types of surgery. For example, if you have liver disease and have been approved for an organ transplant, your doctor may perform a colonoscopy to make sure that you don’t have colorectal cancer before the transplant.

What does a colonoscopy show?

During a colonoscopy procedure, your doctor uses a camera attached to a long tube to visually examine the lining of your colon for growths, inflammation and sores. Based on what they find, they may take a biopsy that’s sent to a lab for testing.

What organs can a doctor see during a colonoscopy?

During the procedure your doctor can see your entire colon, which is also called the large intestine or large bowel.

What can a colonoscopy detect?

Through a combination of visual examination and biopsy analysis, your doctor can identify a range of conditions following a colonoscopy.

Colon polyps

Colon polyps are growths of tissue that start in the inner lining of the colon or rectum. Some lay flat again the colon’s lining, while others have stalks like mushrooms. While most colon polyps don’t turn into cancer, some types are more likely to become cancerous:

  • Hyperplastic polyps and inflammatory polyps – These types of polyps are more common and don’t usually develop into cancer.
  • Adenomatous polyps – Also called adenomas, these polyps are considered precancerous and can develop into cancer.

Most people won’t have any symptoms related to polyps, even precancerous ones. That’s why colonoscopies are so helpful – the procedure allows polyps to be identified and removed before they turn into cancer.

Cancerous tissues

A colonoscopy test is also effective in detecting cancerous tissue. While cancer often starts in polyps, it can also form in abnormal cells, called dysplasia, in the lining of the rectum or colon.

As cancer grows, it can spread to the wall of the colon and rectum. Over time, the cancer can move through all the layers of the colon or rectum wall, affecting blood vessels and lymph vessels. In more advanced stages, the colon cancer can grow beyond the wall, affecting the lymph nodes and other parts of the body.

If your doctor is concerned about cancer or another condition, they’ll likely take a biopsy of suspicious tissues.

Crohn’s disease

Crohn’s disease is an inflammatory bowel disease (IBD). It can affect any part of the digestive tract – from mouth to anus – but it’s usually found at the end of the small intestine and the start of the colon.

People with Crohn’s disease can experience abdominal pain, severe diarrhea, weight loss, fatigue and fever. Also, depending on the location of the Crohn’s disease, people may have symptoms that affect their eyes, skin, liver and joints.

Crohn’s disease usually develops gradually but can also start suddenly. Although there’s no cure, treatment can help manage the symptoms. If left untreated, there may be serious complications.

During a colonoscopy for suspected Crohn’s disease, your doctor will examine the lining of your intestine for inflammation and take a biopsy. If the biopsy shows clusters of inflamed cells (granulomas), it may confirm that you have Crohn’s disease.

Ulcerative colitis is another type of IBD that causes inflammation and ulcers on the lining of your colon. This condition is caused by an overactive immune system that attacks the body’s own tissue. is to know the symptoms you have, how long you have them, and when they’re getting worse. Doing the right things at the right time is essential to bouncing back from a sinus infection.

Symptoms include the urgent need to have a bowel movement, loose and bloody stool, and abdominal cramping. It’s different than Crohn’s disease because ulcerative colitis only affects the colon. And depending on what type you have your symptoms can be pretty mild.

During the diagnostic colonoscopy, your doctor will look for sores, swelling and the location of the disease. What the doctor finds will help them determine if you have ulcerative colitis, Crohn’s disease or something else. They may take a biopsy tissue sample for testing just to make sure.

Microscopic colitis

Microscopic colitis is another IBD that causes inflammation in the colon, which can cause symptoms like watery diarrhea and abdominal bloating and pain. As the name suggests, this type of colitis doesn’t cause visible signs of inflammation, so the tissue must be examined under a microscope. A colonoscopy is one of the procedures that can be used to take a tissue sample for examination.

Doctors sometimes put microscopic colitis into three categories:

  • Lymphocytic colitis where there’s an increased amount of colon tissue created by white blood cells.
  • Collagenous colitis which causes a layer of protein to develop in the colon tissue, making the lining thicker.
  • Incomplete microscopic colitis where a person has both types of microscopic colitis.

Diverticulosis, diverticular bleeding and diverticulitis

Diverticulosis is a relatively common condition caused by small pockets called diverticula in the wall or lining of the intestines. Most of the time, people who have these pockets aren’t aware of them since they don’t usually cause any problems. However, issues with these pockets sometimes cause noticeable symptoms, including:

  • Diverticular bleeding – This is when the pockets bleed, resulting in dark or bright red blood in your poop. A little bleeding is fine, but if there’s a lot, you should see the doctor right away.
  • Diverticulitis – This condition happens when you have an infection or inflammation in the pockets. Diverticulitis can block your bowels, causing constipation or diarrhea, thin stools, bloating, abdominal cramping and a low fever. When you have diverticulitis, you can have severe symptoms that come on very suddenly.

These conditions are usually diagnosed through an examination, bloodwork and sometimes X-rays. But your doctor may also recommend a colonoscopy to confirm that your symptoms are related to the diverticula and not another condition such as colon cancer.


Hemorrhoids, also known as piles, are swollen veins that form inside the lower rectum or under the skin around the anus. There are two types of hemorrhoids: external and internal.

If you have external hemorrhoids – the ones around the anus – you may notice itchiness, discomfort, swelling or bleeding. If you have internal hemorrhoids, you’re likely not even aware of them, but you may experience painless bleeding when you poop. It’s also possible for an internal hemorrhoid to push through the anal opening and cause pain and irritation.

A colonoscopy isn’t typically recommended for diagnosing or treating hemorrhoids since they’re easy to find with a visual or physical exam. But if you have a colonoscopy for another reason, you may find out that you have internal hemorrhoids you weren’t aware of.

Also, if you know you have hemorrhoids, but you’re experiencing certain symptoms like heavy or continuous rectal bleeding, your doctor may recommend a colonoscopy to rule out other possible causes.

What a colonoscopy can’t detect: Answers to frequently asked questions

While a colonoscopy is an incredibly powerful screening and diagnostic tool, it may not be useful for every abdominal symptom.

Can a colonoscopy detect IBS?

No, a colonoscopy can’t detect IBS, a condition also known as irritable bowel syndrome. You may wonder why a colonoscopy can’t detect IBS when it can diagnose the IBD conditions we outlined earlier.

IBS is different from IBD. The biggest difference is that IBS doesn’t change bowel tissue, so there’s no way to identify it during a colonoscopy test – either visually or through a biopsy.

But since IBS is a digestive disorder that affects the large intestine, it has similar symptoms to IBD conditions. Common symptoms of IBS include abdominal cramping, changes in the appearance of your poop and how often you need to go.

So, there’s a chance that your doctor may recommend a colonoscopy to make sure you don’t have IBD or another condition. But if it’s IBS, your doctor won’t be able to find anything to confirm it’s IBS.

Can a colonoscopy detect stomach problems?

No, a colonoscopy only shows your lower gastrointestinal (GI) tract, which is your large intestine and anus. Your stomach is part of your upper GI, along with your esophagus and small intestine. A gastroscopy, also called an upper endoscopy, is used to examine your upper GI.

Abdominal pain and gastrointestinal bleeding can be symptoms of both upper and lower GI conditions. But if you’re also experiencing heartburn, nausea or vomiting, an upper GI condition is most likely.

Can a colonoscopy detect pancreatic problems?

No. Again, a colonoscopy only examines your large intestine and anus. If your doctor suspects that you have a problem with your pancreas, there are different tests they can use for diagnosis. They’ll likely do blood and stool tests to see if there are any abnormalities. They may also use endoscopic ultrasound imaging to get clear pictures of what’s happening inside your body.

Get help for your digestion and colon problems

If you experience changes in your bowel habits, have abdominal cramping or notice blood in your stool, you should talk with your primary care doctor. They can diagnose and treat hundreds of conditions. If you need a colonoscopy, your doctor will share what you need to know about your procedure, including how to make colonoscopy prep easier. And if needed, your doctor will refer you to a gastroenterologist, health, or to a colorectal surgeon who provides medical treatment for conditions that affect the colon, rectum or anus.

Remember that your colon does a lot for you. The main thing, of course, is breaking down food so that it can pass out of your body. But it also plays an important role in your immune system and overall health. So, try to eat a colon-healthy diet and stay up to date on your cancer screenings.

For most people, a colonoscopy is needed just once every 10 years or so. And even though it may not be at the top of your fun list, one colonoscopy can give you peace of mind for years.