What does a positive Cologuard test mean?

Cologuard is a convenient, non-invasive, commercially-available screening test for colorectal cancer. The test is very easy for doctors to order and for patients to complete. There is no bowel prep necessary for this test, and no special diet to follow. The patient doesn’t even need to leave their house to complete the test! Sounds like a pretty good test so far…here’s how it’s done:

Once ordered, the company mails a kit to the patient’s house, and when the urge strikes, the patient places the collection device over the toilet and makes a deposit. There are a few simple preparation steps such as adding in a small amount of liquid that the company provides, and then the entire container is mailed back to the company in the provided packaging. The Cologuard test looks for certain DNA mutations and other abnormalities in the stool to determine if a test is positive or negative. A few weeks later the doctor gets a report indicating the result.

This polyp was found in the rectum of a patient referred due to a positive Cologuard test. It was removed during the colonoscopy: Pathology revealed a tubular adenoma.

This polyp (between red arrows) was found in the rectum of a patient referred due to a positive Cologuard test. It was removed during the colonoscopy: Pathology revealed a tubular adenoma.

The study that determined the characteristics of the Cologuard test basically performed the test on almost 10,000 patients at average-risk of colon cancer, and then had the patients undergo colonoscopy as the gold-standard test. The results of the Cologuard test were not available to the patients or the endoscopist at the time of the colonoscopy. The major results of this study showed that the Cologuard test had an excellent sensitivity (92%) for detecting colorectal cancer. It was far less sensitive for picking up advanced adenomatous polyps (42%). Remember that sensitivity is the main thing we care about in a screening test: we want the test to miss none of the patients who have the disease. A perfect screening test would have a sensitivity of near 100%, meaning that if 10 people have the disease out of the 1000 people screened, all 10 people would get a “positive” test result.

Sensitivity isn’t everything however…we also want a test that gives a negative result when someone does not have the disease in question. Since a full review of statistics is both 1)boring, and 2)not the point of this article, I will cut right to the chase!

What does a positive Cologuard test mean?

First and foremost, a positive result on the Cologuard test means that you need to have a colonoscopy. Not a virtual colonoscopy, or another stool test, or another scan of some sort…you need a real optical colonoscopy. Only about 4% of people will have cancer found on colonoscopy. 51% will have a precancerous polyp. The rest (45%) will have nothing found on colonoscopy. So to simplify even further, just a little more than half of people with positive results will have something abnormal (cancer or a polyp) found on colonoscopy.

What does a negative Cologuard test mean?

A negative test means that there is a less than one-percent (0.06% to be exact) chance of having cancer found on colonoscopy. However, about 34% of people with negative tests still have precancerous polyps found on colonoscopy, with the remainder (66%) of people with negative Cologuard results having truly negative colonoscopies.

What is immediately apparent from these numbers is that Cologuard rarely misses cancer. However, if we count polyps as a significant finding, there are plenty of false-positive results (45%) and plenty of false-negatives too (34%). So is Cologuard a good test overall?

I would argue that it is a great test, with one important caveat: Cologuard is not a replacement for colonoscopy! Colonoscopy is still superior to Cologuard in detecting both cancer and polyps. However, as an alternative to colonoscopy for people who either can’t or won’t get a colonoscopy, Cologuard is an excellent choice. In terms of population-based screening, I think it will get a lot more people screened overall (people who would have otherwise not done anything for screening). When compared to not screening at all, Cologuard is a whole lot better than nothing!

References:

Imperiale TF, Ransohoff DF, Itzkowitz SH, et al. Multitarget stool DNA testing for colorectal-cancer screening. N Engl J Med 2014;370:1287-97.

Cologuard website: http://www.cologuardtest.com/current-patients/how-to-use

  • 			wessoncbob@yahoo.com			

    I recently took a Cologuard test… came back positive… I asked them for the specific results and they refused… why? I suspect that Cologuard is a SCAM. Why would they refuse to at least tell me which of the two samples came back POS??? FDA approved it, but FDA is a tool of Big Pharma, IMO.
    Colonoscopies are dangerous, period. I plan on doing a FIT test twice a year, as the pos result of the Cologuard DOES concern me… wish I had never done it. Dangers of colonoscopies, good series:

    https://www.youtube.com/watch?v=woREV5D1DLQ

    • 			fredgandolfomd@gmail.com			

      Frederick Gandolfo, MD


      The Cologuard test does not report which part of the test came out positive (the fecal blood test or the fecal DNA test), so there is no way to know. However, there is also no reason to need this information because if either one is positive that means that you need further testing to make sure you don’t have colon cancer. It means that you need a colonoscopy, not another FIT.
      I don’t agree that colonoscopies are dangerous (period!) however I am basing my opinion on years of reviewing the pertinent medical literature, intensive subspecialty training, and the experience of personally performing thousands of the exams. In fact, thousands of lives are SAVED every year because of colonoscopies. I think I’ll skip the youtube video…

  • 			mebmus@yahoo.com			

    Colonoscopy is usually a safe test for young, healthy males. Careful reading, however clarifies the risk pools. Risks go up for females, older patients, and especially for post-abdominal-surgery candidates, where a Spanish study of 2018 gave an odds ratio for perforation of 21.59. The probability of adverse consequences for that entire population of 48K was even lower (.033) than the usually cited American risk (.056), but calculating for just that post-surgery group returns a likely risk for perforation at 7.1%. Those of us, like me, who are female, >75, and post-hysterectomy would like to know how to find an endoscopist who can get us through colonoscopy with no adverse consequences.
    I will look forward to your reply. With thanks.

    (Preventive medicine 2018 Nov 08; 118: 304-308: Risk factors for severe complications of colonoscopy in screening programs)

    • 			fredgandolfomd@gmail.com			

      Frederick Gandolfo, MD


      Thanks for the comment. I think you are interpreting the statistics incorrectly however. That study states that out of a total of 48,730 colonoscopies, there were a total of “83 [serious complications] SC were immediate. Of these, 75.9% were perforations and 24.1% were bleeding events requiring transfusion.”
      Therefore there were a total of 63 total perforations, which makes the total risk of perforation 0.13%.
      The odd ratio you refer to are the odds of cases (perforations) in a patient vs. a control subject, NOT the same as saying that the odds of a complication are 21-times higher if a patient had prior surgery etc. They are saying that the odds of a super-rare outcome is 21x higher if you had prior abdominal surgery, vs control patients who didn’t have prior abdominal surgery, since the control patients virtually never have perforations. (The odds of me being struck by lightning are thousands of times higher in the middle of a thunderstorm, but are still very low overall.)
      I cover how to find a good endoscopist to perform a colonoscopy in my free ebook. You can find it on this site and download it.
      Thanks again for the comment!

  • 			cschall@ymail.com			

    Why isn’t there a patient portal online to see your results? It’s either neg or pos. With technology today there should be no reason that a patient shouldn’t be able to go online and see the results instead of waiting 2 weeks to hear from Dr. If the test had to be received within 72 hrs why is it taking so long to get results?

    • 			fredgandolfomd@gmail.com			

      Frederick Gandolfo, MD


      Good question! You should write to the Cologuard people!

      • 			dobbers2@charter.net			

        I had a cologuard test come back positive 4weeks ago. Started checking online to find out what this ment
        According to most sites, I already had colorectal cancer or large precancerous poylp. Only 13% chance of false positive. Therefore I had lots of anxiety waiting 3 weeks for colonoscopy.
        One week before colonoscopy, I found your article. 4% cancer, 51% precancerous, and 45% nothing. Anxiety gone.
        Prep and colonoscopy we’re easy and I had one small benign poylp.
        Don’t waste your time on Cologuard.
        Thank you Dr. Gandolfo for your easy read and informative article.

    • 			cschall@ymail.com			

      I did talk to cologard. You can only talk to cust serv. I pushed for answers and they kept putting me on hold and would come back. I was told by them after 72 hrs the sample is no longer any good. I asked what is the delay. I was told they get so many kits in a day that some have to be put in a freezer. How do they know the sample will give accurate results after 72 hrs. I told her
      what I’m hearing is there are not enough people to do them in the 72 hr period. She said I didn’t say that. I told her I know you didn’t. Just from this conversation that’s what’s happening. I wish I would of just had the colonoscopy but like others I’m a big baby. I told my Dr what was going on. She appreciated. I told her nurse I won’t believe either result. I just hope my insurance will pay for the colonoscopy since they pd for cologard. People get a colonosopy. Skip cologard

  • 			donnaamartin@hotmail.com			

    TOTALLY agree 100% with Cathy Schall. Mine came back positive also, after almost 3 weeks. I also wish I had never taken it. I think I will change primary care physicians for even recommending it, among other things. I am done with Big Pharma! And no, even though I live in a state that has passed medical marijuana, I have not applied for a license, so it isn’t about that. It is that I no longer feel the medical profession can be trusted. Doctors are now “owned” and for the most part, no longer take poride in caring for their patients, as they are “told” HOW to care for them. They are as much a victim, but that does not help me. Wish to God I’d have never taken the damn test.

    • 			skthln@yahoo.com			

      If you are done with “big pharma” you should just drop your doctor completely. I mean, if you are done, then you won’t be able to benefit from any life saving treatments that have come along due to “big pharma”.

      Statements such as this are so ridiculous. You took a test with a high sensitivity and didn’t like the results. Let me tell you, as a wife of a husband with stage 4 colorectal cancer, something that was diagnosed at 36, so wayyyyy before any doctor would have suggested any testing, you should be thanking God that there are these amazing non invasive tests that are available. Go get your colonoscopy for heaven’s sake. Chances are you don’t have cancer. But you could have a polyp that is precancerous. Get it out now and go on with your life. Or, you know, ignore it and have a colostomy bag, liver surgery, lung surgery, chemo, radiation, and all the other Sh*t that comes with advanced cancer. Quit being a whiny baby.

  • 			skthln@yahoo.com			

    Seriously, you are basing your life on a youtube video? I mean, perhaps this is Darwinism at work.

    Lets see here, should I take the word of a non medical professional that produces pseudo-science books full of quackery, or the word of a doctor(s) that has devoted his/her career to gastro diseases. Hmmm, hard choice

    If you had a positive cologaurd test, you need a colonoscopy. They are not dangerous (far more dangerous to drive to your appointment!). The prep for them kind of sucks, but its over in a day. You know what you will like even less then a colonoscopy? Getting a colostomy or ileostomy bag due to having your colon taken out. Or having your rectum removed and your anus sewn shut. Or even better, having your lungs and/or liver riddled with tumors and being told that there is a 11% 5 yr survival rate for stage 4 colon cancer patients. Or you could trust Dr. Quack on Youtube. Good plan

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