Welcome to CRC 101!
The Basics
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What is a colonoscopy?

Colonoscopies are used to detect changes or abnormalities in the lining of your colon and rectum — abnormalities that can result in colorectal cancer over time.

In the US, regular colonoscopy screening starts at age 45, and should be done every 10 years. If you have a higher risk of developing CRC or have recently finished treatment for CRC, these recommendations will be different, so it important to follow the screening advice of your doctor. We will talk more about this later on!

During a colonoscopy, a doctor looks at your intestines with a colonoscope. This is a flexible tube about the width of a finger, with a light and small video camera on the end. It is inserted through the anus, and into the rectum and colon. If your doctor sees anything concerning, they can use special instruments to remove it if small, or take a biopsy (tissue sample) for analysis. 

How do I prepare for a colonoscopy?

Before your colonoscopy, you will need to empty out your colon. Poop can obscure the view of your intestinal walls, meaning your doctor can’t get a good look at the lining of your colon & rectum.

Typically, you will be asked to avoid certain foods, like nuts and seeds for several days before the procedure. Then you will be put on a liquid diet the day before the exam. This means you can only drink clear liquids — plain water, tea and coffee without milk, broth, and carbonated beverages. Don’t drink or eat anything after midnight the day before the exam.

Then, you will take a “bowel prep.” This contains laxatives that help clear the colon and rectum. Speak to your physician about what they specifically recommend. It is very important that you follow the bowel prep instructions carefully or the procedure may have to be repeated.

Discuss your medications with your doctor — especially if you have diabetes, high blood pressure, or heart problems. Tell your doctor if you take aspirin, medications that thin the blood, or contain iron. Your healthcare team will advise you if you need to pause or adjust your medication doses.

What should I do on colonoscopy day?

Arrive at your appointment early. Make sure you get directions ahead of time! Because you will be receiving sedation, you will need to arrange for someone to drop you off and pick you up from your appointment. When you arrive, you will register at the front desk then be asked to change into a gown. 

You will likely be given a sedative. Sometimes the sedative is combined with pain medication to minimize any discomfort. Many patients will be under what is called “twilight sedation” where you will be able to respond to the doctor’s questions, but you will not remember much after the procedure. You will have an opportunity to speak with the doctor before your procedure. 

What happens during the colonoscopy?

The procedure typically takes 30-60 minutes.

The doctor will ask you to lay on your left side on the exam table, with your knees drawn towards your chest. Then, the colonoscope will be inserted in your anus, through your rectum, and into your colon. You may feel some pressure while this is happening, but the sedatives should prevent you from feeling pain or remembering this later. If you feel uncomfortable during the procedure, let the technician know.

The scope contains a tube that allows the doctor to pump air or carbon dioxide into your intestines. This inflates your colon, making it easier to see what’s going on. Being pumped full of air might be uncomfortable — you might feel abdominal cramping or the urge to go to the bathroom.

If the doctor sees anything concerning, they will take a biopsy. Smaller polyps may be removed during the procedure — and if they are, your report will tell you. The sedative will prevent you from feeling any pain during the procedure.

What happens after the colonoscopy?

It will likely take you about an hour to start recovering from the sedative. Make sure you have organized someone to pick you up from the procedure, because it can take up to 24 hours for the sedative to fully wear off. Remember to not drive or go back to work that day.

If a polyp was removed during the procedure, your doctor may advise you to temporarily eat a special diet. 

For a few hours after the exam, you’ll likely feel bloated and farty as you expel the air used in the exam. Don’t worry, this feeling will dissipate quickly. Walking around can help speed up the process!

When you go to the bathroom, you might notice a small amount of blood. This is normal. If you continue to pass blood or blood clots, have persistent abdominal pain, or a fever, contact your doctor. 

How do I get my results and what do they mean?

Your doctor will tell you what they found during the colonoscopy after you recover from sedation. Usually, you’ll be given a report that tells you what was done and the findings of the colonoscopy. If a biopsy was taken or polyps were removed, they will be submitted to pathology for examination. Once results are available, they’ll appear on your patient portal. Your doctor may call you to discuss.

If the colonoscopy was all clear or normal, that means the doctor didn’t find any abnormalities in your rectum or colon. You will likely be asked to come back for another colonoscopy in 10 years if you’re at average risk of colorectal cancer, in 5 years if you have a history of polyps or a family history of CRC, or in 1 year if the doctor could not get a good look at your colon.

If you have recently finished treatment for colorectal cancer, you will need more frequent colonoscopies for the first few years following your treatment. Your doctor will give you recommendations based on your individual diagnosis and risk factors.

If the colonoscopy was not all clear, this means the doctor found polyps or other abnormal tissue. Most polyps aren’t cancerous, but some can be precancerous. You may be asked to come back for a repeat colonoscopy. Please make sure to ask what the results mean for you — because a predisposition for polyps may indicate an increased risk for CRC in your family. So make sure to ask if there is any information that needs to be shared with your family.

How often do I need to get a colonoscopy?

If you are in the US, routine screening for colon cancer begins at age 45. Colonoscopies are then recommended every ten years for screening. People with additional risk factors will need to have them more often, approximately every five years.

If you have been diagnosed with colorectal cancer and have had germline/genetic testing done, the report will provide screening recommendations for your immediate family members. Read them carefully and make sure that you understand them, as they may be different from recommendations for the general population.

If you have been diagnosed with stage I, II or III CRC, you will need to get a colonoscopy one year after your surgery. If the results are normal, then you will come back again after three years, and every five years after that. If polyps are found, then patients are asked to return in a year.

If you have been diagnosed with stage IV CRC and reach NED (no evidence of disease) status, the recommendations are similar. Here are the surveillance recommendations for colonoscopies from the NCCN patient guidelines for colon and rectal cancer.

How useful are colonoscopies?

If the bowel prep didn’t clear your colon and rectum out well, your doctor might not be able to get a good look. They may recommend a repeat colonoscopy, or other exams to image your intestines.

Colonoscopies are highly accurate at detecting CRC, but are not perfect. Overall, this procedure can capture 94% of all colorectal cancer.