Colonoscopy is one method of screening for colorectal cancer. Other methods are also effective and available.

Alternatives to colonoscopy include sigmoidoscopy, which is a less invasive form of colonoscopy, and noninvasive methods, such as stool sample testing.

According to colorectal cancer guidelines published in BMJ, doctors should help people decide on the best screening method and frequency based on their risk of this cancer.

Below, we look at the various tests that doctors use to check for colorectal cancer, as well as the official recommendations for screenings.

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A person can talk to their doctor about the most suitable screening methods.

Medical professionals use colonoscopy to check the large intestine for abnormalities, often when screening for colorectal cancer.

During the procedure, a healthcare professional inserts a long tube, called a colonoscope, into the rectum and along the length of the colon. This tool creates images that help identify colon polyps, and it can also remove them using a small wire loop attached to the tube.

Colonoscopy can be costly, cause uncomfortable side effects, and require substantial preparation and sedation.

Doctors once considered it to be the best screening tool for colorectal cancer, but more recent guidelines acknowledge that other methods can be just as effective, depending on a person’s level of risk and other factors.

Guidelines from the American College of Physicians (ACP), published in 2019, recommend that adults with an average risk of colorectal cancer should undergo screenings between the ages of 50 and 75.

According to the guidelines, a person and their doctor should decide on the method of screening based on a discussion of:

  • the benefits of each technique
  • possible harms
  • costs
  • availability
  • the recommended frequency of screenings
  • the individual’s preferences

Beyond colonoscopy, screening methods for colorectal cancer include:

1. Fecal immunochemical testing

Fecal immunochemical testing (FIT) involves analyzing stool samples. This is a popular screening choice in many areas of the world, and the Food and Drug Administration (FDA) approve its use.

FIT uses antibodies to detect traces of blood in the sample, which indicate that there is bleeding in the gastrointestinal tract.

To help avoid inaccurate results, a person should let their doctor know if they have hemorrhoids or anal fissures, or if they are menstruating before they give the stool sample.

For this test, the person collects a stool sample at home and brings it to their doctor. Most insurance companies cover FIT, and it is low in cost.

A person usually needs to repeat FIT every 1 or 2 years, depending on the doctor’s recommendations.

If FIT results suggest that there is bleeding in the tract, the doctor may recommend colonoscopy for further diagnosis.

2. Fecal occult blood testing

A fecal occult blood test also involves analyzing a stool sample, and it is an alternative to FIT. The ACP particularly recommend high-sensitivity guaiac-based fecal occult blood tests (gFOBT).

For it to screen effectively, a gFOBT should take place every 2 years.

A doctor may recommend having a colonoscopy if the test indicates that there could be an abnormality in the gastrointestinal tract.

3. Stool DNA

This test checks for blood and specific DNA in a stool sample — issues that could indicate the presence of colon cancer. A doctor may use a stool DNA test alongside FIT.

If the test detects any abnormality, the person may need to undergo colonoscopy.

4. Sigmoidoscopy

This is similar to a colonoscopy, but it checks a smaller portion of the large intestine.

Sigmoidoscopy is likewise an invasive procedure that requires preparation, including fasting and taking pills to induce diarrhea or having an enema to clear the colon.

This method is associated with fewer risks than colonoscopy and is often less expensive, but it does not evaluate the whole of the colon.

A doctor can go into more detail about the benefits and risks of colonoscopy and sigmoidoscopy for each individual.

5. CT colonography

CT colonography involves taking detailed images of the colon.

The procedure does not require sedation. However, as with colonoscopy, the person will need to use medications or an enema to clear the colon in advance. A healthcare professional will inflate the colon with air to provide a better view.

If the test detects an abnormality, a colonoscopy is necessary.

6. Double-contrast barium enema

A double-contrast barium enema is a type of X-ray that helps a doctor examine the colon. The barium helps create clear images of the colon.

Doctors rarely use this method because it is less sensitive in detecting small polyps and tumors, compared with colonoscopy. However, it is an option for people at risk of colonoscopy complications.

7. A single-specimen gFOBT

Some doctors collect a single stool sample during a routine rectal examination and analyze it with gFOBT.

However, research has not shown this to be an effective method of screening for colorectal cancer.

Researchers agree that fecal testing, colonoscopy, and sigmoidoscopy are all effective at detecting colorectal cancer.

The most appropriate screening method varies, depending on a person’s risk factors and preferences.

According to BMJ guidelines, yearly FIT or regular sigmoidoscopy or colonoscopy has reduced the incidence of the cancer. However, they note, the incidence reduction of FIT is small, compared with those of sigmoidoscopy and colonoscopy.

Colonoscopies and sigmoidoscopies can help prevent colorectal cancer by finding adenomas, which appear before a tumor develops.

Stool sample tests, on the other hand, cannot prevent colorectal cancer. They can only help a doctor detect it once it is present.

The ACP recommend the following options for adults aged 50–75 with an average risk of colorectal cancer:

  • fecal testing every 2 years, either by FIT or gFOBT
  • a colonoscopy every 10 years
  • a sigmoidoscopy every 10 years plus FIT every 2 years

A range of screening methods can help detect colorectal cancer, including colonoscopy, stool sample testing, sigmoidoscopy, and CT scans of the colon.

If any tests detect abnormalities in the colon, the person will likely need a colonoscopy to help identify the issue.

A doctor will recommend a method and frequency of screening based on a person’s risk factors and preferences.