Nobody looks forward to having a colonoscopy, and it’s true that this colorectal cancer screening test is inconvenient. Beforehand you will need to fast for a day and take a strong laxative to cleanse the bowels. Then you lose at least half a day of work to have the procedure done. Because it involves anesthesiology, you have to recruit a volunteer to drive you home. 

But doctors say a colonoscopy, a way to examine the insides of the rectum and colon (large intestine), is the gold standard for screening for colorectal cancer. It saves lives every day.

While there are easier tests to help detect colorectal cancer, a colonoscopy is one of the best ways to help diagnose it in its early stages, while it is most treatable. It is also the only colorectal screening test that allows the doctor to remove potentially precancerous polyps before they become cancer.

Vikram Reddy, MD, director of colorectal surgery for Yale Medicine, believes colonoscopies are highly effective. They often lead to a cancer diagnosis in time for him to perform lifesaving surgery, while also preserving the patient’s quality of life. “If anyone has any change in their bowel habits, if they have any bleeding—even if they think it’s a hemorrhoid—just get a colonoscopy,” Dr. Reddy advises. 

During a colonoscopy, a doctor examines a patient’s large intestine, or colon, to look for and remove growths that could be precancerous or cancerous. 

Most colonoscopies are done under sedation. The doctor inserts a thin, flexible tube with a tiny light and camera attached to it into the rectum and up through the colon. Photographs or video images of the insides of these organs appear on a monitor, so the doctor can look for growths, such as polyps. The test can also be used to inspect the colon for inflammation, bleeding and ulcers. 

The American Cancer Society and U.S. Preventive Services Task Force recommend that people between the ages of 45 and 75 who are at average risk for colorectal cancer undergo regular screening tests for colorectal cancer. Individuals between the ages of 75 and 85 should talk to their doctor about whether colorectal cancer screening is appropriate for them. Colorectal cancer screening is not recommended for people over 85 years of age.

Several screening tests are recommended, including colonoscopy. For people at average risk for colorectal cancer who choose to undergo colonoscopy screening, it is recommended that they get a colonoscopy once every 10 years between ages 45 and 75.

Colonoscopy is the recommended test for people who are at increased risk for colorectal cancer. Those at increased risk for colorectal cancer may need to begin screening at an earlier age and may have to undergo more frequent screening tests. For instance, a doctor may also want you to take the test earlier if you have a history of colorectal cancer.

An earlier test is also recommended if you have such conditions as inflammatory bowel disease, ulcerative colitis, or Crohn’s disease, which put you at higher risk for getting cancer. Also, your doctor may recommend a colonoscopy sooner if you have such unexplained symptoms as abdominal pain, a change in bowel habits, weight loss, or rectal bleeding. Yale Medicine colorectal surgeons are especially concerned about statistics that show incidence of colorectal cancer is increasing among people younger than 50—even in people in their 20s.

Your doctor will give you detailed instructions on how to prepare for your colonoscopy. The most important thing is to clean out your bowels completely. This enables your doctor to have a clear view of the lining inside your colon during the procedure.

Up to five days before your colonoscopy, you will need to stop taking certain medications, including iron supplements and aspirin—and anything else your doctor identifies. This is also a good time to make arrangements for a ride home after your colonoscopy. Since you will be given anesthesia before the procedure, you will not be able to drive for 24 hours afterwards. Doctors advise against taking public transportation.

On the day before your colonoscopy, you will need to be on a clear liquid diet. This can include clear broth, consommé, coffee and tea (without milk or cream), apple juice, white cranberry juice or white grape juice. You may also have gelatin desserts and popsicles, as long as they are not orange, purple or red.

On that day, you will take pills or drink a gallon of liquid laxative throughout the day. You’ll need to stay close to a bathroom, since the laxative will cause diarrhea.

On the morning of your procedure, you will be able to drink clear liquids up to three hours beforehand. 

Before the colonoscopy begins, you will lie on a table and be given anesthesia. 

There are two kinds of anesthesia used for colonoscopy. One is conscious sedation, which is usually administered by the doctor who performs your procedure. The other is general anesthesia (or deep sedation). If you have the latter, you will be monitored by a credentialed anesthesiologist and nurse anesthetist.

During the procedure, the doctor will insert a tube called a colonoscope into your rectum. The tube has a camera at the end of it. A monitor will display images taken by the camera for the doctor to review. The goal is to find and remove any polyps and other abnormalities.

Your vital signs will be monitored. Most colonoscopies take between 30 minutes and an hour to complete. The general anesthesiology is so effective that most people are surprised when they wake up to discover their procedure is over.

Any polyps will be removed and sent to a pathologist. The pathologist will prepare a tissue sample for analysis, a complex endeavor that takes about a day. The tissue is then examined under the microscope, so the pathologist can determine whether it is benign or cancerous. 

A virtual colonoscopy uses computed tomography (CT) scanning to screen for polyps and masses in the colon. Radiologists interpret these images and report on the findings. If the radiologist discovers any polyps or masses in the virtual colonoscopy scan, the patient may need to have a traditional colonoscopy to remove them.

Because insurance coverage for virtual colonoscopy is not universal in Connecticut, Yale Medicine performs the procedure mostly in cases where a traditional colonoscopy is not possible. This may be because the patient has twists and turns in the colon. Other people have problems with sedation, or they take medication such as blood thinners that make traditional colonoscopy risky. 

When a patient is diagnosed with colorectal cancer, Yale Medicine surgeons treat it using the latest minimally invasive and traditional surgical approaches. They draw upon the expertise of multiple specialists, including oncologists, geneticists, gastroenterologists, and radiologists.

As an academic medical center, Yale Medicine has pathologists who are subspecialists in gastroenterology. They are regularly asked to review diagnoses from community hospitals and other medical centers that do not have these subspecialists on staff. Our pathology team also offers molecular tumor profiling, where they analyze DNA and other biological characteristics of tumor tissue samples. This genetic testing has become increasingly important in providing personalized cancer treatment, including determining the type of medication a patient should get.

Dr. Reddy says surgeons who perform high numbers of a particular surgery tend to have better results than those who perform them less frequently. Yale Medicine surgeons perform one of the largest volumes of colorectal surgery in the region.