Noninvasive Alternatives to Colonoscopy

There are 3 different ways that doctors can look for colon cancer without doing a colonoscopy. Each one has advantages and drawbacks, but can be a good initial screening test if you are not at an increased risk of developing colon cancer. These are the types of noninvasive alternatives:

Stool-based tests

Stool-based tests rely on looking at a stool sample. There are 3 different types of stool tests. 

1. Fecal occult blood test (gFOBT): gFOBT, also called a hemoccult test, checks for blood in your stool that can’t necessarily be seen with the naked eye. It’s easy to do and very inexpensive. The doctor can do it in the office when you have a physical exam. You can also take a kit home with a special card and swab. After a bowel movement you just swab your stool and smear it on the filter paper on the card. You seal the card up and send it back to your doctor. 

 A few drops of a liquid called “guaiac” are placed on the filter. If the color turns blue, it means there’s blood in your stool. This doesn’t mean you have cancer, but it does mean you need to find out why there’s blood in your stool. Your doctor will probably recommend that you get a colonoscopy.

It’s important not to take NSAIDs, eat red meat or have citrus/vitamin C for a few days before the test because they can cause a false positive result.

1. FIT test: “Fecal immunochemical test”(FIT) is done similar to the gFBOT. FIT test is a more specific test, because it uses antibodies to check for blood in the stool. You don’t have to worry about vitamins, medications or what you eat before the test. If it’s abnormal, you’ll need to follow-up with a colonoscopy right away. The FIT test should be done every year.
2. FIT-DNA test: FIT-DNA tests like Cologuard, look for hidden blood. It also detects the abnormal DNA from cancer cells. It’s different from FIT and gFOBT because you’ll need to collect your entire bowel movement in the special container, freeze the container and send it back to the lab in a special package. 

If any abnormal DNA or blood is found, you’ll need a colonoscopy to check for signs of cancer in your colon, such as polyps. FIT-DNA should be done every 3 years if the results are normal.

Radiology test

A CT colonography or “virtual colonoscopy” is done by a radiologist. It uses X-rays to create a 3-dimensional picture of your colon and rectum. Unlike stool tests, it can visualize small abnormalities like tumors or polyps. 

Most people don’t need to be sedated for a virtual colonoscopy. The colon and rectum have to be cleaned out ahead of time using a “bowel prep.” The day before the scan, you’ll be asked to take medications that cause your bowels to completely empty. Stool in the colon will make it hard to read the scans correctly and small polyps might be missed.

Just before the CT scan, you’ll drink a “contrast solution,” which helps show the bowel  lining on the X-rays. A small tube is to introduce air into your rectum and colon. Finally, you’ll need to hold your breath for a few seconds at a time while the scan is done. The main side effect is feeling a little bloated until all the air is passed.

A virtual colonoscopy should be done every 5 years if everything looks ok. If any abnormalities are seen, you’ll need to get a colonoscopy.

Blood test

Blood tests are the latest tools in our arsenal against colon cancer. The Shield Test was the first “liquid biopsy” test FDA approved (2024) for colon and rectal cancer. The test is called a “liquid biopsy” because it uses blood to look for a specific type of cancer; in this case, colorectal cancer. When colon cancer is growing in the gut, cells that die release cancerous DNA into the bloodstream. The abnormal DNA can be detected in the blood by doing a test using antibodies that only recognize genes from cancer cells. The antibodies don’t recognize normal DNA in the blood. This type of DNA is called cell-free DNA (cfDNA) or circulating tumor DNA (ctDNA). The test is only positive if cancer DNA is in the blood.

The advantage of a blood screening test is that it can be done when other routing blood tests are drawn, meaning you’re more likely to follow through and get it done. No bowel prep is needed for the blood test and you don’t have to collect a stool sample.

Since the Shield test was approved last year, several other blood tests have completed testing and are applying for FDA approval. Hopefully, there will be several blood test options available in the near future that offer improvements, like looking for pre-cancerous polyps. 

What are the downsides to colonoscopy screening alternatives?

If you’re ready, willing and able to get colon cancer screening done, one of the noninvasive alternatives might be a good choice for you. The noninvasive alternatives come with a few downsides, however. Some of the disadvantages include:

• They are only options for people who are at “average risk.” If you have any history that raises your risk of colon cancer- a close family member with colon cancer, an abnormal test in the past, or certain genetic conditions– you should opt for a colonoscopy instead.
• They may not find precancerous polyps. Precancerous polyps are best detected with a colonoscopy and they can even be removed at the same time.
• Noninvasive tests are more likely to have false positive and false negative results than a colonoscopy. A false positive test will lead to your doctor recommending a colonoscopy. A false negative test could mean that colon cancer continues to grow inside you until your next screening test. That’s why noninvasive screening tests are done more frequently than colonoscopy.

If you’re reluctant to get a colonoscopy, or unlikely to follow-through with the procedure, staying on top of the noninvasive screening test of your choice is the next best option.