Does a Positive Cologuard Mean I Have Cancer?

Cologuard is a sophisticated stool test that checks for microscopic blood and altered DNA which can signal the presence of colon cancer or precancerous polyps.  Some patients are attracted to this non-invasive option rather than to traditional colonoscopy experience which includes the ever popular cathartic cocktail.

This test was approved by the Food and Drug Administration (FDA) in 2014.   The test was initially quite popular as patients and physicians were enthusiastic about this new colon cancer screening option.  Often in medicine, what’s new becomes popular but initial enthusiasm tends to ebb over time.  (With time, the initial safety and efficacy reports for medicines and diagnostic tests may not be sustained.  This is why post-marketing surveillance after initial approval is so critical.) Patients were advised early on, as they are now, that a positive Cologuard test meant that a follow up colonoscopy was mandatory. Certainly, when I order this test for a patient who is aiming to avoid a colonoscopy, I secure their agreement to a subsequent colon exam if the stool test result is positive. 

Gastroenterologists and physicians in those early years after FDA approval regarded positive Cologuard results very seriously.   This was not yesterday’s stool smear for microscopic blood.  Cologuard detected actual DNA fragments that could be derived from actual cancer or significant colon polyps.

Cologuard detects abnormal DNA fragments.

In those early years, when I was evaluating positive Cologuard patients, I was concerned that these colons had a high probability of harboring significant lesions.  When I was doing colonoscopies on such patients and discovered no abnormalities, I would prolong the exam to re-examine various regions of the colon concerned that I had overlooked the important finding that caused the positive Cologuard.   I often had lingering worry afterwards that I had missed a significant finding.

As the years went by, and the medical profession accumulated more experience, we learned that false positive Cologuard tests were common.  Now, when these colon exams are normal, I recognize that this is a fortunate and common outcome. 

Many positive Cologuard patients are often positive that they have cancer.  The vast majority of them will have either a normal colonoscopy or benign polyps.  So, while I still recommend that every individual with a positive Cologuard result pursue the joy of colonoscopy, the probability that they have an actual cancer is quite low.