A New Option in Colon Cancer Screening: Blood Tests vs Cologuard vs Colonoscopy

Introduction

Colon cancer is one of the few cancers that can often be prevented entirely through early detection and screening. Traditionally, the main options have been colonoscopy or stool-based tests like Cologuard.

Recently, a new blood test was approved for colon cancer screening in adults 45 and older. It’s designed to detect early signs of cancer through a simple blood draw — no prep, no stool collection, and no sedation required. But how does it really compare to the older methods?

What Is the New Blood Test?

The new blood test, called Shield, looks for tiny fragments of DNA shed by colon cancer cells into the bloodstream. It’s intended for people at average risk of colorectal cancer who want a simpler alternative to stool tests or colonoscopy.

In studies, the blood test detected about 8 out of 10 cancers accurately — a promising start for a less invasive screening tool. However, it is not very good at finding precancerous polyps, which means it may miss the opportunity to prevent cancer before it starts.

If a blood test result comes back positive, a follow-up colonoscopy is still required to confirm the diagnosis and remove any polyps or growths.

How It Compares to Cologuard

Cologuard is a stool-based DNA test that looks for traces of blood and genetic markers from abnormal cells in the colon. It’s done at home and mailed to the lab, typically every three years for average-risk patients.

In general:

• Cologuard is slightly more sensitive than the new blood test for detecting existing cancers.

• It also does a better job of identifying precancerous polyps, offering more preventive value.

• However, it can have false positives, which lead to follow-up colonoscopies that may turn out normal.
  

Both tests share one important similarity: if either is positive, a colonoscopy is still needed for confirmation.

How It Compares to Colonoscopy

Colonoscopy remains the gold standard for colon cancer screening. It allows direct visualization of the entire colon and rectum and gives the doctor the ability to remove polyps on the spot, preventing cancer before it begins.

It’s also the most accurate — detecting both cancers and precancerous growths — but it does come with some downsides:

• Requires bowel prep and time off work.

• Involves sedation and some discomfort.

• Carries a small (though rare) risk of complications such as bleeding or perforation.
  

For those who are willing and able, colonoscopy is still the most powerful preventive tool we have. But for patients who avoid it altogether, the new blood test may serve as a helpful “bridge” to getting screened.

When the Blood Test Makes Sense

The blood test may be a good option if you:

• Are 45 or older and at average risk for colon cancer.

• Have avoided colonoscopy or stool tests due to discomfort, inconvenience, or personal preference.

• Would otherwise skip screening entirely.
  

It’s important to understand that while the blood test is more convenient, it does not replace colonoscopy for comprehensive prevention. It’s best viewed as an alternative for people who would otherwise go unscreened.

When to Stick With Colonoscopy or Cologuard

If you have any of the following, you should continue with colonoscopy-based screening:

• A family history of colon cancer or advanced polyps.

• A personal history of polyps, inflammatory bowel disease, or gastrointestinal bleeding.

• Previous abnormal screening results.
  

Patients who want to focus on prevention rather than just early detection will still benefit more from colonoscopy or, secondarily, Cologuard.

The Bottom Line

The new blood test for colon cancer screening represents an exciting step forward — making screening easier and more accessible for those who avoid traditional methods. But it’s not perfect. It’s best seen as an additional option, not a replacement for colonoscopy.

The most important message remains: get screened in some way. Whether through colonoscopy, stool-based testing, or this new blood test, early detection saves lives.

At Woodside Internal Medicine, we help patients choose the screening method that best fits their health, comfort level, and risk factors — so you can stay protected without unnecessary stress.

Disclaimer

This article is for educational purposes only and should not replace professional medical advice. Always discuss your screening options with your healthcare provider to determine what’s best for you.