A Patient Guide to Cancer Screening Blood Tests
Blood tests are becoming a bigger part of the cancer screening conversation. That can be helpful, but it can also be confusing.
If you have heard about Shield, Freenome, Galleri, Cancerguard, or other blood tests, you are not alone. Many patients are trying to sort out what these tests do, who they are for, and whether they replace colonoscopy or stool-based screening.
We want to break it down in plain language for you.
What patients need to know about colorectal cancer blood tests and multi cancer blood tests:
Blood tests for cancer screening are getting a lot of attention. You may be seeing ads, news stories, or social posts that make it sound like one blood test can answer every question about cancer screening.
That is where things can get confusing.
A blood draw may feel simpler and easier to fit into daily life than a colonoscopy or stool test. But not all cancer blood tests are designed to do the same job.
Some blood tests are designed to look for colorectal cancer specifically. Others are designed to look for signals from many cancers at once. These are often called multi cancer early detection tests, or MCED tests.
At Fight CRC, we want patients to have clear, practical information that helps them ask better questions and make informed decisions.
| Test | Company | Type | Main purpose | Current status | Key patient takeaway |
| Shield | Guardant Health | Single cancer blood test | Colorectal cancer screening | FDA approved for average risk adults 45 and older | Designed for colorectal cancer screening, but positive results still need colonoscopy |
| Freenome CRC test | Freenome, licensed to Abbott Laboratories in the U.S | Single cancer blood test | Colorectal cancer screening | Investigational | Important emerging option, but not the same as an approved screening choice today |
| Galleri | GRAIL | MCED blood test | Looks for signals from many cancers | Commercially available, not FDA approved | Not a colorectal cancer screening test and does not replace standard screening |
| Cancerguard | Abbott Laboratories | MCED blood test | Looks for signals from many cancers | Commercially available as an LDT, not FDA approved | Not a colorectal cancer screening test and does not replace standard screening |
| Shield MCD | Guardant Health | MCED platform under study | Looks for signals from many cancers | Research setting | Different from Shield CRC screening and easy for patients to confuse |
| Avante ct MCD | ClearNote Health | MCED platform under study | Looks for signals from many cancers | Research setting | Another emerging platform being studied in national trials |
What is the difference between a colorectal cancer blood test and an MCED test?
| Question | Colorectal cancer blood test | MCED blood test |
| What is it designed to find? | Colorectal cancer | Signals linked to many cancers |
| Is it a colorectal cancer screening test? | Yes, if it is specifically designed and approved or validated for that purpose | No |
| Does it detect polyps or precancers? | Sometimes, but current blood based CRC tests are much less effective at finding advanced precancerous lesions than cancer itself | No. MCED tests are not designed to find colorectal polyps or precancers |
| Can it diagnose cancer? | No | No |
| What happens after a positive test? | Colonoscopy is usually the next step | Additional workup, often imaging and sometimes procedures |
What do sensitivity and specificity mean?
These terms can sound technical, but the ideas are simple.
| Term | Plain language meaning | Why it matters |
| Sensitivity | How often the test finds cancer when cancer is really there | Higher sensitivity means fewer cancers are missed |
| Specificity | How often the test is negative when cancer is not there | Higher specificity means fewer false alarms |
| False positive | The test says something may be wrong when no cancer is found | Can lead to stress, imaging, procedures, and extra cost |
| False negative | The test misses a cancer that is actually present | Can create false reassurance |
In everyday terms:
- Higher sensitivity means the test is better at finding cancer when it is there.
- Higher specificity means the test is better at avoiding false alarms.
- False positives can lead to more testing, more worry, and more cost.
- False negatives can create false reassurance and delay follow up.
Why Precancer Matters in Colorectal Cancer Screening
This is one of the most important things to understand.
Colorectal cancer screening is not only about finding cancer early. It is also about finding advanced precancerous lesions before they turn into cancer.
That is why a test should not be judged only by whether it can find cancer that is already there. In colorectal cancer, the ability to catch precancer matters too.
What Patients Should Know About MCED Tests
MCED tests are designed to look for signals from many cancers, not specifically to screen for colorectal cancer.
Patients may hear about tests such as Galleri and Cancerguard. They may also hear about MCED platforms under study such as Shield MCD and Avantect MCD. The National Cancer Institute (NCI) selected Shield MCD and Avantect MCD for its Vanguard Study, which shows how quickly this area is evolving. (NCI Vanguard Study)
The most important takeaway for patients is this: MCED tests do not replace recommended colorectal cancer screening. The American Cancer Society says blood-based tests are not currently included in the ACS colorectal screening guideline, and the USPSTF says its colorectal cancer screening recommendation does not include serum tests because of limited available evidence. (American Cancer Society screening tests page, USPSTF recommendation)
A simple way to think about MCED tests:
- They may sound broader, but broader does not mean they replace standard screening.
- They are not colorectal cancer screening tests.
- A positive result can lead to additional workup, including imaging or other follow up testing.
Common questions about blood tests for cancer screening
| If you are asking… | The most helpful answer is… |
| I want screening specifically for colorectal cancer | Choose a colorectal screening option with your doctor based on your risk level, symptoms, and which test you are most likely to complete |
| I want a blood test instead of a stool test or colonoscopy | Ask whether you are average risk and whether a blood based CRC screening option is appropriate |
| I want one blood test to replace all screening | No blood test does that today |
| I want a test that looks for many cancers | Understand that MCED tests are different from colorectal screening tests and do not replace standard screening |
Questions patients should ask before choosing a blood test
These questions can help start the conversation with your doctor:
- Am I average risk or high risk for colorectal cancer?
- Is this test meant for colorectal cancer specifically or for many cancers?
- Is this test FDA approved, investigational, or offered as a laboratory developed test?
- How well does it detect colorectal cancer?
- How well does it detect advanced precancerous lesions?
- What happens if my result is positive?
- What happens if my result is negative but I have symptoms?
- Will my insurance cover the test and any follow up testing?
- Would a stool based test or colonoscopy be a better fit for me?
Bottom line
Blood tests are becoming a bigger part of the cancer screening conversation, but patients still need clear information.
A colorectal cancer blood test is not the same as a multi cancer blood test.
Some blood tests are designed for colorectal cancer screening. Others are designed to look for many cancers at once. They have different goals, different evidence, and different follow up steps.
What matters most is understanding:
- what the test is actually designed to find
- whether it fits your risk level
- what the next step will be if the result is positive
- whether a different screening option may be a better fit for you
The best screening choice is the one that fits your risk, your questions, and the next steps you are willing and able to take.
And whatever option you choose, do not ignore symptoms and do not assume one blood test can replace every recommended screening test.
For readers who want to review the guidance directly, start with the American Cancer Society colorectal cancer screening guideline, the American Cancer Society screening tests page, and the USPSTF colorectal cancer screening recommendation. (ACS guideline, ACS screening tests page, USPSTF recommendation)
Blood Test FAQ:
Can a blood test replace a colonoscopy?
No. A blood test cannot replace colonoscopy in every situation. If a colorectal cancer blood test is positive, colonoscopy is usually the next step. The FDA also states that Shield is not a replacement for diagnostic or surveillance colonoscopy. (FDA Shield approval)
Are multi cancer blood tests the same as colon cancer blood tests?
No. MCED tests and colorectal cancer blood tests are built for different purposes.
- MCED tests look for possible signals from many cancers.
- Colorectal cancer blood tests are designed specifically around colorectal screening.
Is a negative blood test enough to rule out colorectal cancer?
No. A negative test does not rule out cancer and should not override symptoms or medical advice. The FDA says a negative Shield result does not guarantee that a person does not have colorectal cancer. (FDA Shield approval)
Does insurance cover a colorectal cancer blood test or an MCED test?
Sometimes, but coverage is uneven and depends on the test and your insurance.
- Medicare covers blood-based biomarker screening tests for colorectal cancer every 3 years for eligible adults ages 45 to 85 who are at average risk and have no symptoms. Medicare says you pay nothing if your provider accepts assignment. (Medicare blood based biomarker screening coverage)
- Medicare also says that if you have a positive result from a Medicare covered blood based colorectal screening test, it covers a follow up colonoscopy as a screening test. (Medicare colonoscopy coverage)
- Private insurance coverage for colorectal cancer blood tests is still evolving and can vary by plan, network, and whether the test is included in that plan’s preventive benefits.
- MCED tests are often not covered by insurance. Galleri says most health insurance plans do not cover the test, and Cancerguard says it is not currently covered by health insurance. (Galleri cost and coverage, Cancerguard request page)
If I pay out of pocket for the blood test, will that cause problems getting follow up testing covered?
It can, depending on your insurance and what follow up care is needed.
- With Medicare, the clearest coverage language applies when the original blood based colorectal screening test itself is Medicare covered. Medicare says a positive result from a Medicare covered blood based biomarker screening test can be followed by a covered screening colonoscopy. (Medicare colonoscopy coverage, Medicare blood based biomarker screening coverage)
- With private insurance, patients should not assume that paying cash for the original test automatically guarantees coverage of all follow up imaging, procedures, or colonoscopy. Plans may treat follow up care differently depending on whether the first test was covered, whether the next step is considered screening or diagnostic, and whether the provider and facility are in network.
- For MCED tests, follow-up may include imaging or other diagnostic workup, and Galleri states that the cost of the test does not include that diagnostic testing. (Galleri for HCPs)
A practical way to protect yourself is to ask these questions before testing:
- Is this test covered by my plan?
- If the result is positive, is the next step considered screening or diagnostic?
- Will the follow up colonoscopy, imaging, lab work, or specialist visits be covered?
- Do I need to use a specific in network lab, doctor, or facility?
Reference Links:
American Cancer Society colorectal cancer screening guideline: https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/acs-recommendations.html
American Cancer Society colorectal cancer screening tests page: https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/screening-tests-used.html
USPSTF colorectal cancer screening recommendation: https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening
FDA Shield approval information: https://www.fda.gov/medical-devices/recently-approved-devices/shield-p230009