With Stool Testing, Fewer Americans May Delay Colon Screening

The test arrived in a compact envelope along with illustrated instructions: Lay the tissue paper in the toilet so it can catch the stool. Then, use the finger-length probe to collect a portion of that stool and place it in the sample bottle. Label the sample bottle, wrap it in the enclosed absorbent pad, and put it inside the plastic biohazard bag. Tuck the bag into the return mailer and ship within 72 hours.

“I wasn’t keen on doing the procedure part of it,” said 50-year-old Leslie Fresch, who lives in Austin, Texas. “But I got it done, because I knew it was important.”

Fresch’s stool test was part of a larger project led by researchers from the University of Texas at Austin. Beginning in 2017, more than 20,000 tests were sent to patients treated at CommUnityCare, a network of clinics for primarily underserved populations in Central Texas, including patients without insurance. Before the project, nearly one in five patients were up to date on colon screening. By 2019, an additional 19 percent of those eligible had completed screening with a stool test.

At $55 per patient for the test and related reminders, this type of stool testing, also known as a fecal immunochemical test, or FIT, is the most cost-effective approach for this underserved group, said Michael Pignone, a primary care physician at UT Austin’s Dell Medical School who leads the research. “In our population, if we spent our money on screening colonoscopies rather than on stool-based screening, we’d be able to serve far fewer people.”

Even before the pandemic, just two-thirds of Americans got timely colon screening. Since then, rates for several cancer screenings, including colorectal, have declined. Last year, the recommended age to start colon screening was lowered from 50 to 45 years old for those at average risk, expanding the pool of eligible adults. Meanwhile, this fall, results published in the New England Journal of Medicine from the first large and rigorous study of the benefit of offering colonoscopies have called into question whether making screening available is quite as effective as prior research indicated.

Stool testing must be done more frequently than colonoscopies. Even so, some researchers and physicians are starting to ask whether the lowly stool test — convenient, affordable, and with no documented risks — should be more often promoted as a viable alternative. People typically don’t realize there are other methods, said Christopher Almario, a gastroenterologist at Cedars-Sinai in Los Angeles.

“A lot of times people think colonoscopy is synonymous with colorectal cancer screening,” he said. “But a lot of people don’t want to do colonoscopy.”

Almario co-authored a recent study that educated unscreened adults about screening methods and then asked them to choose between an annual stool test or a colonoscopy, which is recommended every 10 years. A majority of respondents in the survey selected the stool test, including 77 percent of those 50 and older.

“Ultimately,” said Almario, “the best test is the test that gets done — that the patient is willing to do.”

Colorectal cancer remains the third leading cause of cancer death for both men and women in the U.S., taking about 53,000 lives annually. Screening rates through one of various methods are highest among White adults, at 68 percent, compared with Black adults (65 percent), Hispanic adults (59 percent), and Asian adults (55 percent), according to the most recent federal data from 2018.

The FIT and colonoscopy are the two tests most highly recommended in a screening guideline published in 2017 and jointly authored by several gastroenterology groups. The U.S. Preventive Services Task Force recommendation, published last year, includes various screening options, including colonoscopy, which looks at the entire colon; sigmoidoscopy, which looks at the lower portion; and stool testing. But the Task Force doesn’t rank them in any preferential order.

There are several types of stool tests used in the United States. Both the FIT and the high-sensitivity guaiac fecal occult blood test work by detecting blood in the stool. Of the two, only the FIT requires one stool sample and no changes in diet ahead of time. A newer DNA test detects blood as well as genetic mutations that might indicate cancer. That test has a higher likelihood of false positives compared with the FIT test, leading to more follow up colonoscopies, according to the Task Force.

For the U.S. health system broadly, and for uninsured patients in particular, stool tests are significantly less costly than colonoscopies. Stool tests are also less time-consuming and invasive. During a colonoscopy, the colon is inflated with either air or carbon dioxide in order to accommodate a flexible tube with a tiny camera. The camera scans the rectum and colon, allowing a physician to look for potentially cancerous growths. For the procedure to work, the colon must be empty, so patients are required to take a laxative and make numerous bathroom trips beforehand.

A fecal immunochemical test, or FIT, which is used to screen for colon cancer, is convenient, affordable, and has no documented risks. Some researchers and physicians are starting to ask whether it should be more frequently promoted as a viable alternative to a colonoscopy.
Visual: UCLA Health/YouTube

Yet in the U.S., just 11 percent of adults ages 50 and older rely on stool testing to look for colon cancer, according to federal data. Far more individuals, 61 percent, reported getting a colonoscopy within the prior decade.

Those numbers might be due, in part, to financial incentives, said Rita Redberg, a physician at the University of California, San Francisco, who has critiqued colonoscopy’s status as the optimal method. “It’s a lot simpler to do a fecal test,” she said. “But the gastroenterologists cannot bill for a fecal test.”

Ma Somsouk, a gastroenterologist at Zuckerberg San Francisco General Hospital, agreed. “There’s an incentive within the health system to do more colonoscopies,” said Somsouk, noting that not only does the physician get paid but the hospital gains a facility fee.

How much a colonoscopy costs is difficult to nail down, as it varies based on insurance coverage, where it’s performed, and other elements. Medicare reimbursement rates range between $600 and $1,000, including physician and facility fees. David Lieberman, a gastroenterologist at Oregon Health & Science University, said that the procedure, including sedation, can easily cost a few thousand dollars. A recent article detailing a billing dispute shows that insurance may pay as much as $4,000.

Under the Affordable Care Act, colon screening, including stool tests and other options listed in the Task Force statement, must be free for insured patients once they reach the eligible age. That free coverage extends to patients who have already taken a stool test and received a positive result, according to guidance that federal officials released in early 2022.

Primary care physicians may also have an incentive to steer patients to colonoscopy, said Theodore Levin, a gastroenterologist and clinical lead for colorectal cancer screening at Kaiser Permanente in Northern California. When a person decides to take a stool test, the onus is on the primary care physician to ensure the patient receives and takes the mail-in test. If the result is positive, the physician will typically recommend a colonoscopy. Physicians are not always reimbursed for their extra time, said Levin, and they may be inclined to avoid the stool test.

There’s also the perception that spotting and removing any growths from the colon is inherently beneficial, said Somsouk, who has studied the use of stool tests to reach underserved populations. But, he added, “I don’t think that we have the data to clearly prove that colonoscopy is better.”

“There’s an incentive within the health system to do more colonoscopies,” said Somsouk.

Gastroenterologists have marketed colonoscopy as the gold standard, Levin acknowledged. “So many people feel like if they’re not getting colonoscopy, they are getting kind of substandard care,” he said, “which is not necessarily completely supported by the evidence.”

Colonoscopy proponents describe the procedure as the gold standard test, citing it as the best screening approach to prevent the disease. During the procedure, physicians can remove any bumps on the inner lining of the colon, called polyps, that can potentially develop into cancer.

While larger polyps are more likely to become malignant, physicians typically remove all visible polyps no matter how small to ensure they don’t miss any malignancies, said Rick Boland, a retired gastroenterologist in San Diego and an author on the 2017 gastroenterologists’ joint screening guideline. “The pathologist has to look at the polyp under the microscope and tell us what it is.”

And with a stool test, there’s an ick factor to start. “The bottom line is people don’t like to mess around with their stools,” Boland said. The test needs to be repeated frequently — from one to several years depending upon the method — and people will still need a colonoscopy if the test is positive. The FIT test also can pick up bleeding from other causes, such as hemorrhoids. Some cancers may be missed if they don’t bleed at all.

Still, both screening approaches are “effective, and both of them have their advocates,” Boland said.

Almario, who cites a recent study showing waiting lists for screening colonoscopies, argues that encouraging more lower-risk adults to consider stool testing could free up space for patients who are more likely to have colorectal cancer, due to a family history or a positive stool result. As it is, he said, the U.S. health care system “cannot handle doing a colonoscopy for every 45- to 49-year-old at this point.”

Prior to the fall publication of the New England Journal of Medicine paper, previous findings from less rigorous studies indicated that colonoscopies could significantly impact diagnoses and deaths. One analysis of 29 studies, for example, found the procedure reduced colorectal cancer diagnoses by 52 percent and deaths by 62 percent.

The NEJM study authors ran a randomized controlled trial, an experimental design that aims to eliminate bias by randomly assigning study participants to two or more groups. In this study, which randomly assigned nearly 85,000 adults across several European countries, one group was invited to get a colonoscopy — similar to what happens in the real world — while the other group wasn’t offered any screening. The researchers then followed the study participants for a decade to see which group had lower rates of colon cancer.

The participants in the invited group weren’t any less likely to die from colorectal cancer over a decade, but diagnoses declined by 18 percent, according to the findings. In the invited group, 259 people developed cancer versus 622 in the group who weren’t invited.

If this seems like a small benefit, it may be because enthusiasm for colonoscopy was not strong; only 42 percent of invited individuals followed through.

Those who did get a colonoscopy had a 50 percent lower risk of colorectal cancer death, noted Lieberman, who heads up an American Gastroenterological Association committee to improve colon screening. This result demonstrates that colonoscopy “can be extremely effective,” he said, for patients who actually undergo the procedure.

“The bottom line is people don’t like to mess around with their stools,” Boland pointed out.

Studies that compare the effectiveness of colonoscopy to stool testing are ongoing, but the results will take time. One U.S.-based study that Lieberman is involved with, which has enrolled slightly more than 50,000 U.S. adults, will track study participants over 10 years. It is currently estimated to wrap up by 2028.

But the recent findings provide yet another reminder that longstanding health assumptions don’t necessarily hold up once randomized studies are completed, said Redberg, who has long studied the benefits and risks of medical care, including screenings. If patients aren’t randomized, differences between the groups can skew the results, she has written. For instance, adults who get a colonoscopy might be healthier than those who do not.

Plus, the procedure is not risk-free. For every 10,000 colonoscopies, there are 14.6 major bleeding episodes and 3.1 perforations of the colon, according to data provided in the Task Force colon screening statement.

And in the U.S., the procedure is often performed with sedation, said Redberg, which carries additional risks. “When someone is sedated, they don’t feel the pain,” she said. If, as a physician, “you cut something you shouldn’t have,” she said, your sedated patient likely won’t realize and speak up.

According to the UT-Austin researchers, stool testing could reduce longstanding disparities in colon cancer screening, by reaching more adults who are uninsured or live in rural areas. CommUnityCare patients can struggle to get to the clinic for any medical treatment, never mind preventive care like cancer screenings, said Eda Baykal-Caglar, who directs education and research there, and collaborates with the UT-Austin researchers. “Some of our patients say they cannot take time off because they need to work; they’re the bread earners of their households,” she said.

Soon after Leslie Fresch completed her stool test, a physician told her that it had picked up traces of blood and referred her for a colonoscopy. The procedure this fall was easy, she said, other than the “horrible stuff” she had to drink the day before. A polyp was removed, and Fresch was told that she doesn’t need to return for 10 years.

Three-quarters of CommUnityCare adults with positive stool findings, nearly 200 patients, got a colonoscopy. Eight of them were diagnosed with cancer.

At Kaiser Permanente Northern California, an even larger program built around mailing FIT tests annually along with providing colonoscopy upon request dramatically boosted screening rates in that insured population. The initiative, which began with a pilot study in 2006, doubled the percent of individuals current on screening from just under 40 percent in 2000 to nearly 83 percent by 2015, according to the study findings.

A later analysis, which followed screening results from the program through 2019, found that it had reduced the higher rates of colorectal cancers and deaths among Black adults to nearly the rates of White adults. One possible explanation, Levin said, is that Kaiser Permanente’s systematic approach helps eliminate any disparities in treatment. “You’re not relying on an individual physician to remember to invite someone to screen, or advise them to get screened, which is where implicit bias might play a role,” he said.

For those adults who can afford either screening test, Pignone said, they should be offered a choice based on their preferences. He’s opted for colonoscopy. “I personally would rather do something once every 5 or 10 years and get it out of the way than do it every year,” he said.

In some circumstances, colonoscopy might be optimal, Levin said: “If you absolutely need to know and are uncomfortable with any uncertainty about what’s going on in your colon — that’s the advantage of colonoscopy.” But even then, there are no guarantees, he added. Physicians can miss cancers in the colon or rectum, or they can appear between procedures.

Since Levin turned 50, he has gotten the FIT test annually, believing that he should “walk the walk” given his research. Plus, “it’s just so convenient,” he said. “It takes five minutes. I do it once a year in the privacy of my house, walk out to the mailbox right afterwards, drop it in. And then I’m done.”

Charlotte Huff is a Texas-based journalist who writes about the intersection of medicine, money, and ethics. Her work has appeared in Kaiser Health News, Slate, STAT, and Texas Monthly, among other publications.