I often receive questions like this from people around me. "I heard that a blood test can check for colon cancer, so does that mean we don't need colonoscopies anymore?" Honestly, I was intrigued at first too.

Anyone who has experienced the process of drinking the bowel prep solution and running to the bathroom all night knows how uncomfortable it is. If it could be replaced with just a tube of blood, who would refuse?

So this time, I set aside emotions and looked at the numbers. To sum it up, blood tests are "definitely better than not doing anything, but they cannot replace colonoscopies."

First, let's clarify the facts. The FDA approved a blood test called Shield from Guardant Health as a primary screening test for colon cancer in July 2024. The target group is adults aged 45 and older who are at average risk.

In July of this year, Freenome's SimpleScreen CRC received FDA approval as the second option. Abbott has announced that it will be released this fall, adding another choice.

So how effective are these tests? The ECLIPSE study, which provided the basis for Shield's approval, involved over 20,000 participants from the average-risk group, and the sensitivity for detecting colon cancer was 83%.

SimpleScreen showed a sensitivity of 81.1% for colon cancer in the PREEMPT CRC study, which included over 48,000 participants. At first glance, these numbers seem quite good.

The problem arises next. The ability to detect advanced adenomas, or precancerous lesions, drops significantly.

According to the FDA label data for Shield, the sensitivity for advanced adenomas is 13%. SimpleScreen was nearly the same at 13.7%. I was somewhat surprised by these numbers.

In simple terms, blood tests are useful for finding cancer that has already developed, but they often miss the opportunity to remove precancerous lesions before they turn into cancer.

The true value of colonoscopy lies here. By removing polyps on the spot, the examination itself becomes a preventive measure.

The Shield label also notes that the sensitivity for early-stage cancer is even lower, and that even if a blood test result is negative, there could still be precancerous lesions that would have been detected during a colonoscopy in 1 out of 10 cases.

Perhaps for this reason, major medical organizations are cautious. The American Cancer Society updated its colon cancer screening guidelines on May 27 of this year, including blood tests in its recommendations for the first time.

However, they classified it as a "nonpreferred" option, meaning it is only recommended for those who refuse visual examinations like colonoscopies or stool tests.

In the same update, two at-home stool tests, Cologuard Plus and ColoSense, were also added. This suggests that if you want a non-invasive test, stool tests are preferred over blood tests.

The blood test is recommended every three years. It's worth noting that this is more frequent than colonoscopies, which are typically done every 10 years if results are normal.

And here's an important point: whether it's a blood test or a stool test, if the result is positive, you will ultimately need to undergo a colonoscopy. The ACS recommends getting it done within six months if possible.

Let's also touch on costs. Medicare covers FDA-approved blood-based colon cancer tests once every three years according to the National Coverage Decision (NCD 210.3).

Regular health insurance varies by plan. Be sure to call your insurance company before the test to check if it will be processed as preventive screening and what your out-of-pocket costs will be for follow-up colonoscopy if the result is positive.

Let's confirm the age criteria as well. The ACS recommends regular screenings starting at age 45 and continuing until age 75 for those at average risk.

Individuals at high risk due to family history or inflammatory bowel disease are not eligible for blood tests. The Shield label also states that it cannot replace surveillance colonoscopies for high-risk individuals.

So what would I do? If I can get a colonoscopy, I would just go for it. The return on investment is clear when a day of discomfort can lead to 10 years of peace of mind.

If I find colonoscopies really scary or can't find the time, I would consider stool tests like FIT or Cologuard next. If that's not an option either, I would choose a blood test.

Still, I want to emphasize one thing: it's much better to have a blood test than to do no testing at all. The real significance of this technology is in attracting people who have been postponing screenings altogether.

Especially for those who have been putting off going to the hospital due to busy schedules or language barriers, this could be a tool that lowers the threshold for access. I welcome this improvement in accessibility.

However, which test is right for your situation depends on family history, past test history, and insurance conditions. Be sure to discuss with your doctor before making a decision.

In summary, blood tests are convenient but do not effectively catch precancerous stages. Therefore, it's more accurate to view them as a "minimum safety net" rather than a first choice.

If you haven't had a screening this year, start by calling your primary care physician's office this week. That's the first step, even before any test.