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At-home screening test is effective alternative to colonoscopy, study finds

At-home screening test
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In the first year of this study, FIT detected colorectal cancer in 84.5 percent of participants who were diagnosed with the disease.

An at-home non-invasive screening test for colorectal cancer that can detect microscopic amounts of blood in stool is a “feasible and effective” alternative to colonoscopy, even if used year after year, according to a study published this week in the Annals of Internal Medicine.

That last finding is important, as health experts had been concerned that the effectiveness of this method of colorectal cancer screening — known as the fecal immunochemical test (FIT) — might wane after the first year an individual used it.

The findings also suggest a way of reaching the third of American adults for whom preventive colorectal screening is recommended, but who have never been screened or who are not up to date with it. Many people avoid colonoscopy because of the long and uncomfortable preparation it requires, as well as the invasiveness and unpleasantness of the test itself. Others can’t afford the screening. They are either uninsured, or loopholes in their insurance require high co-pays for the procedure.

Colorectal cancer kills about 52,000 people annually in the United States, making it the nation’s second leading cause of cancer death, according to the Centers for Disease Control and Prevention. It is also one of the most curable types of cancer — if diagnosed and treated early 

Screening for colorectal cancer can be very effective, and is recommended for people who are 50 to 75 years old, which is the age group at greatest risk of developing the cancer. FIT is simple and inexpensive, but needs to be done every year. Colonoscopy is a much more complicated and expensive procedure, but is required only once every 10 years.

A four-year study

For this study, researchers at Kaiser Permanente in Oakland, Calif., analyzed data collected from 323,349 of their health plan members between the ages of 50 and 70 who participated in FIT screening for colorectal cancer over a four-year period. (Those numbers represented about half of the people who were originally sent the screening test and asked to participate.)

To use FIT, people collect a small sample of their stool and then mail it to a laboratory, which looks for microscopic amounts of blood that might indicate a slowly bleeding polyp or cancerous tumor. FIT is similar to, but not the same, as the fecal occult blood test, which uses a different laboratory technique and is not considered quite as effective as FIT at detecting colorectal cancer.

In the first year of this study, FIT detected colorectal cancer in 84.5 percent of participants who were diagnosed with the disease. In the next three years, the test picked up between 73 and 78 percent of the cancers.

“We found that the sensitivity for cancer was somewhat higher in the first year, and that's not surprising,” said Dr. Douglas Corley, a Kaiser Permanente research scientist, in an interview with HealthDay reporter Dennis Thompson. “The first year you screen someone, for breast cancer or for anything, you’re going to find cancers that have been there for a while that may be larger or are easier to detect.”

High adherence

Another positive finding from the study was that adherence to the screening was high: 86 percent of the participants completed the test for all four years.

All those numbers combined led Corley and his colleagues to conclude that FIT was “both feasible and effective” for screening large groups of people.

Again, this is good news for people who have avoided getting screened for colorectal cancer because they dreaded (or couldn’t afford) a colonoscopy.

“There are a couple different effective tests for colorectal cancer screening, including colonoscopy and FIT,” Corley said in his interview with HealthDay. “They have different strengths and weaknesses. This study provides additional support that FIT can be an important tool for getting more people screened in a way that is both sensitive to picking up cancers and making it easier for people to comply.”

FMI: You’ll find the abstract of the study at the Annals of Internal Medicine website, although the full study is behind a paywall. For information about colorectal cancer, including screening, go to the National Cancer Institute’s website on the disease.

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Comments (2)

False positives

Does the article discuss the rate of false positives with this test?

False Positive Rate for FIT

At least in its abstract, this journal article doesn’t provide the specificity rate, and so you can’t obtain an estimate of the False Positive rate directly. It does give the “positive predictive value” for CRC and a sensitivity rate for FIT for just CRC. If you supply some CRC incidence rate estimate to those taking this test, you can solve for the False Positive rate from the “positive predictive value” and a sensitivity rate. These incidence rates vary quite a bit by age and some, but less dramatically, by gender, with most new cases (~ 90%) occurring among those > 50 years old. Given the range of CRC incidence rates by age groups (50-64, ≥ 65) and gender from the most recent data of the Amer. Cancer Society, I get a range of False Positive rates of from 1.1% (Fem 50-64) to 5.5% (Male ≥ 65) from this study’s results.

There was a meta-analysis of FIT testing results in the Ann Intern Med in 2014 and its specificity rate was 0.94 (CI, 0.92 to 0.95), giving a False Positive rate between 5% and 8%. I have seen another study’s results from Holland of FIT testing, and from its abstract results, which give the rate at which those taking the test have a positive test result (positivity rate) and the proportion of those positive tests that were later confirmed on subsequent colonoscopy to have advanced adenomas or cancer, I infer a False Positive rate also right around 5%.

But I, not an MD to be sure, think that the way to think about FIT testing is that it’s very easy and agreeable to take, and if your test comes back positive, then you go on to have a full colonoscopy. But the totally agreeable thing about FIT testing—besides its not being a colonoscopy—is that if your test does return negative, the (negative predictive value) is such that you’re essentially 100% sure you don’t have CRC. They do recommend taking the FIT every year, however.