Cologuard vs Colonoscopy: Don’t Be Fooled by the Marketing

Medically reviewed by: Gary H. Hoffman, MD
Last modified on January 4th, 2024

Colorectal cancer is the fourth leading cause of new cancers and the second leading cause of cancer-related deaths in the United States. 

Unfortunately, colon cancer is often a disease with silent signs or symptoms in the early stages. That’s why it’s important to get screened regularly for colorectal cancer, especially if you have a positive family history.

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In 2014, the FDA approved Cologuard as a screening tool for colon cancer, which seems an attractive option since you don’t have to be sedated as you do before a colonoscopy. It is marketed as detecting colorectal cancer in its earliest stages.  But how reliable is it? And who should take it?

To summarize, Cologuard is not accurate or sensitive enough to replace colonoscopies for colon cancer screening. This is especially true for high-risk patients, such as those with a family history of the disease.

And when there are tools to detect pre-cancerous polyps BEFORE they become malignant, why would we use an inferior tool to see a potentially deadly disease when it could have been detected in its benign stage?

Nonetheless, as colorectal surgeons in Beverly Hills, we always look towards the future with patient health and outcomes in mind. We embrace new technologies as they develop (like we did with laparoscopic surgery in the 1980s and robotic surgery in the 2010s) and analyze new procedures and methodology through an objective lens. As such, we are actively following how Cologuard is evolving, and in this article, we review the technological advancements thus far.

What is Cologuard? What is a colonoscopy?

Cologuard is a non-invasive test that checks your stool for DNA mutations, blood, and abnormal cells that may indicate the presence of cancer. The test is done at home, and you do not need to be sedated as you do for a colonoscopy.  And no bowel preparation is necessary.

A colonoscopy is a procedure in which your doctor examines the inside of your large intestine with a lighted tube equipped with a camera. It’s a direct way to identify and remove any abnormalities or precancerous polyps

In other words, a colonoscopy is a direct way to screen for cancer, whereas Cologuard uses an indirect methodology.

Although Cologuard is an approved screening tool for colorectal cancer, it is not very popular with healthcare providers. We’ll find out why in later sections.

How to use Cologuard?

To use Cologuard, you’ll need a doctor’s prescription and meet certain eligibility requirements. Once you have a prescription, you can order Cologuard through a Cologuard website, and the test kit will be shipped to your home.

The kit includes instructions on collecting your stool sample and a prepaid shipping label to send the sample back to their laboratory. The process takes about 10 minutes, although it could take longer if you’re not used to collecting stool samples. 

To ensure accuracy, you must ship the sample back within 24 hours of collection.

Once the laboratory receives your sample, they test it for DNA mutations, blood, and abnormal cells and send the results back to your doctor. Your doctor will then discuss the results with you in their office. 

Who should not use Cologuard?

Cologuard is not recommended for those who have already had a positive screening test, such as an abnormal fecal occult blood test. In this case, a colonoscopy should be done to confirm the results.

It should also not be used by people at a higher-than-average risk for colorectal cancer. These include those with inflammatory bowel disease (such as ulcerative colitis and Crohn’s disease), a family history of colorectal cancer, or a known cancer-causing hereditary syndrome like Lynch syndrome.

Finally, Cologuard is not recommended for those with colorectal cancer or polyps, as it’s unreliable for detecting recurrent colorectal cancer.

Is Cologuard more accurate than a colonoscopy?

No, Cologuard is not more accurate than a colonoscopy. A colonoscopy is the most accurate and sensitive of all the screening tests for colorectal cancer. The sensitivity of a test refers to how well it can detect pre-existing cancer or polyps.

In comparison, Cologuard has a 92.3% sensitivity rate for detecting colorectal cancer, while a colonoscopy is 95% sensitive. But remember, colonoscopy detects PRE-CANCEROUS polyps, while Cologuard does not.

FIT-DNA = Cologuard.

FIT-DNA = Cologuard. Source

But here is the main problem.   A colonoscopy is 75% sensitive for detecting a small adenoma — a pre-cancerous growth that turns into cancer — while Cologuard is only 17.2% sensitive in this case.

Similarly, a colonoscopy is 85-95% sensitive for detecting moderate to large adenomas, while Cologuard is far behind at only 17-40% sensitive.   The larger the adenoma, the greater the chance that it will be, or already is, malignant within the body of the polyp.

This brings us to our next question — can Cologuard miss cancer?

Can Cologuard miss cancer?

Yes, Cologuard can miss cancer. However, this is not very common because, as we saw above, the test has a 92.3% sensitivity for established cancer.

But what Cologuard can very easily miss are precursors to cancer (or adenomas). This means that it might not show up as positive even though you have a precancerous growth in your colon. Over time, this growth may turn into cancer, rendering Cologuard a failure as a screening tool.

This is supported by a 2019 study by researchers at Mayo Clinic Rochester, Minnesota, which found that Cologuard can miss precancerous growths, especially if they are larger.

On the other hand, there have also been reports of false positives with Cologuard. This means that Cologuard may sometimes show up as positive even when there’s no colorectal cancer present.

For example, in this review of Cologuard that evaluated 1585 patients, researchers found that it has a positive predictive value (PPV) of only 7.7% for precancerous polyps and cancer. 

This means that out of every 100 patients who test positive for Cologuard, only eight have cancer or precancerous growth. 

The researchers concluded: “Multitarget stool DNA (or Cologuard) testing carries an unacceptably low PPV to be utilized as a screening test for colorectal cancer. The study fails to detect adenomas and colon cancer at a higher rate than screening colonoscopy in selected studies”.

As you can imagine, this can be very stressful for people, leading to unnecessary follow-up tests and procedures.

This is in contrast to colonoscopy, which does not carry a high risk of false positives, giving patients peace of mind when they test negative. 

Does a positive Cologuard test mean cancer?

No, a positive Cologuard test does not mean cancer. It’s important to understand that Cologuard is a screening tool for cancer. And most screening tests out there aim to catch cancer before it develops.

When Cologuard is positive, it has picked up something suspicious in your stool sample. This does not necessarily mean you have cancer, but you might have something that can turn into cancer if not promptly removed.

This is why doctors never diagnose colorectal cancer based on Cologuard test results. If someone has a positive Cologuard test result, they will usually be asked to undergo a colonoscopy. 

If the doctor finds growth on colonoscopy, it will be biopsied, meaning a small piece of tissue will be removed and tested for cancer. Only then can a definitive diagnosis be made.

Plus, as we’ve already discussed, there’s always a chance of false positives with Cologuard, so a positive test doesn’t mean you have cancer.

What is the best test for colon cancer?

The best colon cancer test is a colonoscopy with a biopsy. This is especially true for those at higher risk for colorectal cancer, such as those with a family history or a known hereditary cancer syndrome.

In addition to diagnosing colon cancer, a colonoscopy can also remove it during the same procedure. This spares you from needing to undergo a separate surgery later on.

But of course, a colonoscopy has its drawbacks. For one, it’s an invasive procedure, and you’ll need to come to an outpatient surgicenter.

You’ll also need to prepare for colonoscopy by taking a laxative the day before to clear out your bowels, as well as having someone drive you home after the procedure because of sedation.

In addition, some people don’t react well to the sedatives used during a colonoscopy, and there’s a small risk of complications like colonic perforation.

A Cologuard test doesn’t come with all these problems, but it’s also not as accurate as a colonoscopy.

The best way to figure out which test is the best for you is to talk with your doctor. They’ll be able to consider your age, risk factors, and overall health when deciding.

You should get a colonoscopy, not cologuard

If you’re feeling a bit lost after all of that information, here’s a quick summary:

  • Cologuard is a new stool-based screening tool for colorectal cancer.
  • People may use Cologuard at average risk for colon cancer. Those at a higher-than-average risk should undergo a colonoscopy.
  • You will need a doctor’s prescription to take the Cologuard test, which will be shipped to your home.
  • A positive Cologuard result doesn’t mean you have cancer. A positive test is always followed up by a colonoscopy and biopsy, which is the only way to make a definitive diagnosis of colorectal cancer.
  • Cologuard is not more accurate than a colonoscopy for detecting precancerous lesions.

If you have more questions about Cologuard, feel free to contact us!

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