Colonoscopy

A colonoscopy is used to check for polyps or colorectal cancer, or to find the cause of symptoms such as changes in bowel habits, bleeding, or weight loss. It’s done by a gastroenterologist, a specialist in the digestive tract.

What is a colonoscopy?

A colonoscopy is a procedure used to look inside the colon and rectum, which are part of your digestive system. This test is different from a virtual colonoscopy (CT colonography), which is a type of CT scan.

This procedure is done with a colonoscope, a long, thin, flexible tube with a light and camera on the end. It’s put in through your anus into the rectum and colon. Special tools can be passed through the colonoscope to take samples or treat problems, if needed.

Why might you need a colonoscopy?

There are a few reasons you might need a colonoscopy.

Screen for colorectal cancer

A colonoscopy can be used for colorectal cancer screening. Screening means looking for cancer in people who don’t have symptoms.

If abnormal areas are seen during colonoscopy, they can be removed (biopsied) by passing special tools through the colonoscope. The samples are then looked at under a microscope in the lab to see if they are cancer.

A colonoscopy can also prevent some colorectal cancers by finding and removing polyps (growths on the inner lining) before they turn into cancer.

Check for problems in the colon or rectum

Colonoscopy can be used to look for the causes of signs or symptoms that might be from colon or rectal cancer such as changes in bowel movements, bleeding from the rectum, pain, unexplained weight loss, or other non-cancerous conditions.  

If you have had colon or rectal cancer, colonoscopy can be used to detect new tumors. It can also be done for people at high risk for colorectal cancer due to a personal history of adenomatous polyps, those with a family history of polyps, or those with certain family cancer syndromes.

Treat colon or rectum problems other than polyps

Colonoscopy can be used to monitor or treat problems in the colon or rectum such as blockages (obstruction) or bleeding.

For some advanced cancers that can’t be removed because they are too big or have spread, a colonoscope can be used to place a rigid tube called a stent into part of the colon or rectum to help keep it open.

What’s it like to have a colonoscopy?

This is a general outline of what often happens before, during, and after a colonoscopy. Your experience might be a little different, depending on why you’re having it, where you’re having it done, what prep is required, and your overall health.

Be sure to talk to your doctor before having this test so you understand what to expect. Ask questions if there’s anything you’re not sure about.

Before your colonoscopy

Be sure your doctor knows about any medicines you are taking, including vitamins, herbs, and supplements, as well as if you have allergies to any medicines.

You might be asked to stop taking blood-thinning medicines, including aspirin, for several days before the test to reduce the risk of bleeding. Your doctor might also ask you to adjust some medicines, such as those for diabetes, or stop others, such as iron. If you normally take prescription medicines in the morning, talk with your doctor or nurse about how to manage them on the day of your test.

You will be given instructions by your health care team on what to eat and drink in the days leading up to the test. It is very important that you follow these instructions as failing to do so might affect the procedure or the results of the test. In general, you will be asked to:

• Eat a low-fiber diet, avoiding foods such as nuts, whole grains, and raw fruits and vegetables for a few days before the test. This will make bowel prep easier.
• Drink only clear liquids such as broth, black coffee, gelatin, and clear juice, starting 1 day before the test up to a certain time set by your health care team.
• Stop eating or drinking anything after a certain time the night before your test.

Because a sedative is used to help keep you comfortable during the procedure, you will need to arrange for a ride home after the test. If you are sleepy or dizzy, you might need someone to help you get safely into your home, so a cab or a rideshare service might not be a good option. Some clinics will not allow you to use a cab or rideshare after this procedure.

If transportation or help getting home might be a problem, talk with your health care provider. There might be other resources available, depending on the situation.

What is a bowel prep and why is it needed?

For a colonoscopy, the colon and rectum must be empty and clean so your doctor can see well during the test. You might hear this referred to as a bowel prep. There are different ways to do this, such as pills, liquids, enemas, or combinations of these. Talk to your health care provider about all your options for the bowel prep. They will prescribe one for you to follow.

Many preps involve drinking liquid laxative solutions, sometimes in large amounts, along with electrolytes the evening before the procedure. This often results in frequent trips to the bathroom. Newer options include pills that you take by mouth. They might make the bowel prep process easier.

It’s important to read the instructions carefully a few days ahead of time, since you might need to shop for supplies and laxatives. If you’re not sure about any of the instructions, call the health care provider’s office and get your questions answered.

During your colonoscopy

Colonoscopy can usually be done as an outpatient procedure, where you don’t need to stay overnight in a hospital. Your doctor will review the procedure with you and ask you to sign a consent form. For this test, you’ll change into a hospital gown and lie on your side on an exam table with your knees pulled up.

Your blood pressure, heart rate, and breathing will be monitored. You’ll likely get sedative and pain medicines through an intravenous (IV) line to help you relax, or less often, be asleep (under general anesthesia) for the test.

The doctor will gently insert the lubricated colonoscope into the rectum through your anus, up to the beginning of your colon. Air is added to help the doctor see more clearly. If you’re awake, you might feel pressure or an urge to have a bowel movement. As the scope is slowly pulled out, the doctor will carefully check the inside of the colon and rectum.

If a small polyp is found, it might be removed and then sent to a lab to check for cancer. If your doctor sees a larger polyp, tumor, or an abnormal area, a small sample will be taken through the scope and tested to see if it’s cancer, a benign (non-cancerous) growth, or something else.

The doctor might also treat any narrowed or blocked areas, depending on why the colonoscopy is being done.

The test itself usually takes about 30 minutes, but it might take longer if polyps are found and removed.

Is colonoscopy painful?

Many people feel some discomfort during a colonoscopy, but it’s usually not painful. The type of sedation that is used is called conscious sedation, which helps you relax and be less aware of what’s happening. You might be awake or fall asleep, and you might feel some pressure or mild cramping. Tell your health care team if you’re uncomfortable so they can help.

Some people cannot have conscious sedation because of other health conditions. In these cases, deep sedation with general anesthesia might be used. This means you are fully asleep and closely monitored by an anesthesia specialist.

Having no sedation is also an option, though it’s uncommon.

After your colonoscopy

After the procedure, you will be watched closely for any problems for about an hour before you are able to go home. If you had a sedative, you might not remember the procedure.

You might feel bloated, have gas pains, or get cramps from the air used during the test. If you had the procedure as an outpatient, you should be able to go home after a few hours.

If you were given a sedative, someone will need to drive you home and stay with you until it wears off. Your doctor or nurse will give you specific instructions to follow after the test, including when to start taking medicines again that might have been stopped for the procedure.

If biopsies were taken, test results are usually ready within a few days, although some might take longer. You will need to follow up with your doctor after the procedure to get your results.

Possible risks of colonoscopy

Colonoscopy is usually safe, but there are some risks.

Bleeding: If a polyp is removed or a biopsy is done during the colonoscopy, you might notice some blood in your stool for a day or 2 after the test. Serious bleeding is uncommon, but in rare cases, bleeding might need to be treated or can even be life-threatening.

Perforation (puncture of the wall of the colon or rectum): This is rare, but it can be a life-threatening complication, and the hole might need to be repaired with surgery.

Drug reactions: Sometimes the drugs used to help you relax and stay comfortable during a colonoscopy can cause changes in blood pressure, confusion, dizziness, or even an allergic reaction. You will be watched closely for any medicine side effects and they will be treated, if needed.

When to call your care team

Before you go home, your doctor or nurse should give you specific instructions on when you might need to call the doctor’s office for problems. In general, these include:

• Severe abdominal (belly) pain
• Fever
• Swelling or distension in your belly that lasts after a few days
• Bloody bowel movements
• Dizziness
• Weakness

Be sure you understand what you should watch out for, the possible timing of when problems might occur, and when you should call for problems.