The American Cancer Society updated its colorectal cancer screening guidelines on Wednesday, officially adding blood-based testing as a recommended option for average-risk adults aged 45 and older. This shift provides an alternative for individuals who are unable or unwilling to complete traditional visual exams, such as colonoscopies, or stool-based screening methods.
Expanding Screening Options for Colorectal Cancer
Colorectal cancer remains a major public health concern, with recent trends showing an increase in cases among younger populations. While clinical experts maintain that colonoscopies remain the gold standard for detection—allowing physicians to physically examine the colon and rectum and remove warning signs like polyps—the physical and logistical barriers associated with these exams have led many patients to skip screening entirely.
American Cancer Society
To address these gaps, the American Cancer Society has updated its guidance to include blood-based screening. The specific test now endorsed is the Shield test, manufactured by the biotech firm Guardant Health, which received approval from the U.S. Food and Drug Administration in 2024. This inclusion marks a significant change in how health organizations approach patient compliance, acknowledging that the most effective screening test is often the one a patient is actually willing to complete.
The updated guidelines also emphasize new advancements in stool-based testing, including the introduction of Cologuard Plus and the FDA-approved ColoSense, developed by Geneoscopy. Like earlier iterations, these tests allow for at-home sample collection, which are then processed in a laboratory to identify molecular markers associated with colorectal cancer.
Clinical Context and Limitations of Blood-Based Tests
Despite the addition of blood testing to the recommended list, medical professionals are careful to define its role within a broader diagnostic strategy. Research published in CA: A Cancer Journal for Clinicians indicates that these blood tests are not intended to replace established visual or stool-based diagnostics for the average patient. Instead, they serve as a secondary pathway for those who have declined or failed to complete other, more sensitive options.
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“At this time, blood‐based tests should be recommended only to individuals who decline or do not complete preferred screening tests, because it’s not as sensitive as the other testing options in detecting precancerous polyps, but I do think it is the right option for the right population of patients.”
American Cancer Society's new guidelines for breast cancer testing
Dr. William Dahut, chief scientific officer for the American Cancer Society
The primary concern cited by experts is sensitivity. While a blood test can detect circulating markers of cancer, it is currently less effective at identifying precancerous polyps compared to a colonoscopy. However, the potential for increased participation rates is viewed as a major benefit. By removing the “squeamishness” associated with fecal sample collection or the invasiveness of a colonoscopy, health officials hope to capture a larger percentage of the eligible population.
“There are a lot of people who can’t or won’t do a colonoscopy, or the idea of collecting their own stool for testing, they just won’t do. Having more options hopefully will allow more people to be screened to find cancers earlier on, and we’ll be able to cure more patients.”
Dr. William Dahut, chief scientific officer for the American Cancer Society
Understanding the Biological Components of Blood
The shift toward blood-based diagnostics highlights the increasing precision of blood analysis in modern medicine. Human blood is a complex tissue comprised of several specialized components, each performing vital transport functions. According to the Cleveland Clinic, an average adult possesses between 4 and 5 liters of blood, which circulates through the body to deliver oxygen and nutrients while removing metabolic waste.
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Plasma: A yellowish fluid making up about 55% of blood volume, primarily composed of water, proteins, and salts.
Red blood cells: Erythrocytes, which account for approximately 44% to 45% of blood volume, contain hemoglobin to transport oxygen.
White blood cells and platelets: These constitute roughly 1% of blood volume and are essential for immune response and clotting, respectively.
As noted by Britannica, the body maintains the composition of these components through highly regulated feedback systems, such as the kidney’s release of erythropoietin (EPO) to stimulate red blood cell production. Because blood is a transport liquid that reaches nearly every part of the body, it serves as a unique medium for detecting systemic signals, including the molecular markers now utilized in the ACS-recommended cancer screening tests.
Looking Ahead: The Role of Screening in Patient Outcomes
The move to incorporate blood-based testing reflects a broader trend toward personalized screening protocols. By diversifying the available methods, the medical community aims to reduce the mortality rate associated with late-stage colorectal cancer. Early diagnosis remains the most significant variable in patient survival, as it allows for intervention before symptoms manifest.
Patients are encouraged to discuss these updated options with their healthcare providers to determine which screening method is most appropriate for their specific risk profile and personal preferences. As the adoption of these new tests proceeds, the focus will remain on monitoring how effectively they bridge the current gap in population-wide screening compliance.
Dr. Nadia Rowe oversees medical, science, and wellness reporting. Holding a public-health doctorate and having contributed to Health Spectrum Review, she bridges scientific rigor with accessible communication. Her mission: make accurate health information available to everyone.
