What is a colonoscopy?

Gastroenterologists use colonoscopy to screen for colorectal cancer. This minimally invasive endoscopic procedure enables doctors to examine the lining of a patient’s rectum and large intestine (colon) for abnormalities.

When they perform a colonoscopy, gastroenterologists pass an endoscope or colonoscope (i.e., a thin and flexible tube with a light and camera on the leading end) through a patient’s rectum and into the colon. Doctors then carefully examine the lining of the patient’s colon for polyps or any other abnormalities. If any polyps are detected, they remove them using a small snare that’s attached to the endoscope/colonoscope. Most colorectal cancer can be prevented by removing these polyps.

In addition to using this procedure to screen people for colorectal cancer, gastroenterologists use colonoscopy to evaluate patients who have colorectal bleeding, abdominal pain and chronic diarrhea. This is known as a diagnostic colonoscopy.

Gastroenterologists also perform surveillance colonoscopies to examine patients who have had colon polyps removed in the past.

Why it is crucial to get screened for colorectal cancer?

Some 130,000 Americans are diagnosed with colorectal cancer (cancer of the colon or rectum) every year — and nearly 50,000 of them die from the disease. Colorectal cancer is the second leading cause of cancer deaths in the U.S. behind lung cancer, yet more than 30 percent of the adults in this country aren’t getting screened for this disease.

The good news is that colorectal cancer has a 90 percent survival rate when it’s detected early enough. In fact, gastroenterologists can detect this disease in a person before they exhibit any symptoms. It has been estimated that greater colorectal cancer awareness and screening could save at least 30,000 lives in the U.S. each year.

Current national guidelines recommend that every man and woman (who get the disease in equal numbers) should be screened for colorectal cancer as soon as they turn 45 — even if they haven’t exhibited or experienced any problems or symptoms.

Patients who are under 45 and have high-risk conditions may need to get screened for colorectal cancer on a more regular basis. High-risk conditions include:

  • Family history of colorectal cancer or precancerous polyps in a first degree relative diagnosed before age 60
  • Multiple first-degree relatives with colorectal cancer or precancerous polyps
  • Family history of inherited colorectal cancer syndrome
  • Previous diagnosis of ulcerative colitis or Crohn's disease

Patients should talk to their primary care physician or gastroenterologist about the need to get screened for colorectal cancer.

Why is colonoscopy the optimal colorectal cancer screening option?

There are several ways physicians screen their patients for colorectal cancer, including colonoscopy, flexible sigmoidoscopy, fecal immunochemical (FIT) or stool tests and MT-sDNA (Cologuard) or virtual tests. Colonoscopy is the only test to prevent colorectal cancer, with its unique ability to remove polyps before they turn into cancer. It is the only screening test recommended at 10-year intervals, because it’s by far the best test at finding precancerous polyps. This is important because far more invasive treatments like surgery and/or chemotherapy are required once colorectal cancer develops. Plus, a colonoscopy is still required if a stool test or CT scan flags any abnormalities.

How long does a colonoscopy take?

Colonoscopies are generally performed on an outpatient basis that takes about 30 to 45 minutes to complete. In some cases, patients are given a mild sedative that enables them to relax and make them sleepy during the procedure to minimize any discomfort — which can include abdominal pressure, bloating or cramping. In other cases, patients receive an anesthetic that puts them completely asleep during the procedure.

Do colonoscopies ever have complications?

Colonoscopy is a common outpatient procedure. It does not require hospitalization. Complications from a colonoscopy are rare, but they can occur. This includes a perforation (i.e., a hole or tear) in the gastrointestinal tract lining, which may require emergency surgery. If a biopsy is taken or a polyp is removed during a colonoscopy, bleeding may occur. This bleeding is usually minor, and it normally stops on its own, but it can require additional treatment. A patient’s heart rate, blood pressure or breathing may also change because of the medications that are used to perform a colonoscopy. So while complications after a colonoscopy are uncommon, patients should not hesitate to contact their doctor immediately if they experience any complications following a colonoscopy, including running a fever or abdominal pain or bleeding or black stools.

What happens if the doctor finds polyps or other abnormalities?

It is not unusual for gastroenterologists to find growths or polyps on the lining of a patient’s colon when they perform a colonoscopy. These polyps come in different shapes and sizes. Because most polyps are pre-cancerous — which means they can develop into colorectal cancer — gastroenterologists generally remove them on the spot using a tiny wire loop that is called a snare, although patients may be referred to a specialist to remove polyps that are unusually large.

Most polyps are typically sent to the pathologist to be checked if they are precancerous or not.

If a gastroenterologist discovers any other abnormalities while they are performing a colonoscopy, they can pass a tiny device through the endoscope/colonoscope to obtain a tissue sample for testing (i.e., biopsy). These devices are also sometimes used to remove polyps.

When a gastroenterologist performs colonoscopy on a patient who is bleeding from the colon, they may inject medications into the affected area. They may stop the bleeding using a heat treatment that is known as cauterization, or they may apply small metal clips to the affected blood vessels. These procedures are usually not painful.

Colonoscopy is the optimal way to prevent colorectal cancer because it allows gastroenterologists to fi nd and remove polyps on the spot.

What are patients required to do before a colonoscopy?

Patients are generally limited to a clear liquid diet (e.g., gelati n) the day before they have a colonoscopy. They also need to undergo a bowel preparation process that will empty and clean their colon the evening before the exam. There are now various ways of doing bowel preparation, including consuming lower amounts of the solution or taking pills, making the process more agreeable for many. This process takes a few hours, and it is the only way to ensure that a gastroenterologist can examine a patient’s colon in a full and comprehensive way.

Patients can continue to take most of their normal medications before a colonoscopy, although some are known to interfere with the bowel preparation process or the safety of the procedure. Patients are consequently encouraged to let their gastroenterologist know about any medications they take, especially insulin or other diabetes medications, aspirin products, arthritis medications, blood thinners (e.g., warfarin, apixaban, rivaroxaban, heparin, etc.) and other drugs that interfere with clotting (e.g., clopidogrel/Plavix, ticagrelor, prasugrel, etc.). Patients should not take over-the-counter medications and supplements on the morning of the procedure.

Patients are also encouraged to let their gastroenterologist know about any medical conditions they have, including heart or kidney or lung disease. And, they should tell their doctor if they are allergic to any medications or latex.

Finally, it is essential for patients to follow their doctor’s instructions before and after they have a colonoscopy.

What happens after a colonoscopy?

Following a colonoscopy, patients are free to go home once most of the effects of any medication or anesthesia have worn off , although they will be required to have a family member or friend drive them home. Patients should also not drive or operate machinery or make legal decisions on the day of the procedure — even if they feel alert after the procedure, as the medications that are used for colonoscopy can affect one’s judgment and reflexes for the rest of the day.

Some patients experience mild discomfort, bloating or pass gas because of the air that is introduced during the examination. Those symptoms usually go away within a day. Patients can also resume their usual diet once the exam is done unless their doctor instructs them to do otherwise. Gastroenterologists normally share the preliminary results of the procedure with their patient on the day of the exam, but the results of some tests like biopsies may take several days.

How often a patient needs their next colonoscopy depends on several factors, which include:

  • How clean their colon was during the procedure (i.e., whether the doctor was able to conduct a full and comprehensive exam)
  • How many pre-cancerous polyps were removed
  • The size of the largest polyp that was removed
  • Whether any of the polyps that were removed had any troubling features (e.g., early cancer)

Once gastroenterologists have this information, they will recommend when the patient should get their next colonoscopy (normally the next three, five or 10 years).

How to find a gastroenterologist in your community

Patients who need to schedule a colonoscopy can visit to fi nd an ASGE member gastroenterologist in your community who has received specialized training in performing this procedure.

Important Reminder: This information is intended only to provide general guidance. It does not provide definitive medical advice. It is very important that you consult your doctor about your specific condition.