It is also one of the most preventable — if caught early, the five-year survival rate exceeds 90%. And yet more than 45 million eligible Americans are due or overdue for screening. While education of colon cancer symptoms and screening guidelines exist, patients still have to contend with understanding of and access to screening tools.
Colonoscopy remains the gold standard, but completing one requires bowel prep, sedation, time off work, and an available specialist. Depending on the research study, only 20 to 40% of patients actually follow through with the entire colonoscopy. For those who complete screening, guidelines for average-risk adults who get a clean colonoscopy result ask patients to return in up to 10 years for repeat colonoscopy.
That 10-year gap is where Kim Turner’s story lives.
Colonoscopy screening intervals
Turner, a physician assistant in Alaska, had her first colonoscopy at 50, which found a one-centimeter precancerous polyp. Her follow-up at 54 was clear. She has no family history of cancer, obesity, or smoking. Her gastroenterologist told her she didn’t need another colonoscopy for 10 years.
In 2025, Kim’s daughter organized a health fair and suggested a blood-based colorectal cancer screening test called Shield, by Guardant Health. Kim agreed casually. “I didn’t expect it to come back positive,” she said. However, at just 61, 3 years before being due for her screening colonoscopy, the blood test returned positive.
A follow-up colonoscopy confirmed adenocarcinoma in a three-centimeter section of her sigmoid colon. She has no rectal bleeding, abdominal pain. The only symptom she could recall was very mild and intermittent constipation, which her doctors had attributed to an unrelated condition. Constipation can be a symptom of colorectal cancer, though in Kim’s case it was subtle enough, and explained away convincingly enough, that it never raised a red flag. “I effectively had no symptoms,” she said. “I was shocked.”
Shortly after diagnosis she had surgery to remove the cancerous mass along with 28 lymph nodes, one of which was positive. That, along with minor vascular involvement, classified her as Stage 3. At the time of this interview, she was in the middle of a twelve-week chemotherapy regimen.
She was three years from her ten-year screening and the single mild, intermittent symptom she had was attributed to another medical condition.
“If I would have waited three years,” she said, “very different story. Very different.”
How does Shield testing impact colon cancer screening?
In a clinical trial of more than 20,000 participants, it demonstrated 83% sensitivity for colorectal cancer and 90% specificity, putting it within range of other recognized non-colonoscopy screening options.
The company recommends testing every three years and it is currently covered by Medicare. Dr. Craig Eagle, the former Chief Medical Officer at Guardant Health, explains the test simply: when a colorectal tumor is present, it continuously sheds tiny fragments of its DNA into the bloodstream. Shield analyzes a blood sample for those fragments, looking for cancer-specific patterns. This is a test that can be ordered by a primary care doctor as an outpatient.
Eagle wants to set correct expectations about the use of Shield in patient care. He states clearly that Shield is not a colonoscopy replacement, “Colonoscopy remains the gold standard.” As well, a positive result with Shield still requires a follow-up colonsocopy. Where it stands out, however, is that it offers is a lower-friction option for the millions who have not completed a colonoscopy on schedule for various reasons: fear, access, scheduling, cost. “We have the best test available to all, colonoscopy, and only 20 to 40% of people actually complete it, depending on the study,” says Eagle, “No matter how good the test is, if it’s not done, it’s a waste of time.”
The American Cancer Society’s updated 2026 guidelines now include blood-based testing as a screening option, though they classify it as secondary to colonoscopy and stool tests. The FDA label uses stronger language, designating Shield as a frontline indicated choice. That gap in recommendation reflects a genuine clinical debate the field is still working through.
As a physician myself, I am still telling patients to prioritize colonoscopy, but if they are declining the more invasive test, supplemental blood-based testing, like Shield, or stool-based testing, like Cologuard or ColoSense, should be discussed.
What is less clear is if there is a role for these less-invasive tests to be used in between longer stretches of colonoscopy screening periods, to assure no disease has progressed while still preserving resources required for colonoscopies.
Limitations around Shield testing
Like any medical test, you need to know what is best for the patient infront of you. Shield states on their website a two key disclaimers.
1. Shield has limited detection (55%-65%) of Stage I colorectal cancer and does not detect 87% of precancerous lesions. One out of 10 patients with a negative Shield result may have a precancer that would have been detected by a screening colonoscopy. Shield demonstrated high detection of Stages II, III, and IV colorectal cancer.
2. The Shield test is not indicated for patients that have personal history of colorectal cancer, adenomas, or other related cancers; or those who had a positive result on another colorectal cancer screening method within the last six months, have been diagnosed with a condition associated with high risk for colorectal cancer such as Inflammatory Bowel Disease (IBD), chronic ulcerative colitis (CUC), Crohn’s disease; or who have a family history of colorectal cancer, or certain hereditary syndromes.
This language is critical for all patients because it clarifies that the test, like most medical diagnostics, is not perfect and there are limitations in how it can be used and how the results can be interpreted.
Education around colon cancer symptoms and screening guidelines
Kim has agreed to share her story publicly for one reason: “You don’t want to wait until you have symptoms,” she said.
Her case raises a question patients increasingly want the medical community to answer. Is a ten-year screening interval too long, especially for patients with a prior polyp history? And for the tens of millions who won’t complete a colonoscopy regardless of the reason, do simpler less-invasive tools, such as blood tests, stool kits, deserve a more prominent place in the standard algorithm?
As of now, here is no formal answer and a lot to consider about simpler less-invasive tools. False positives carry real costs: unnecessary procedures, anxiety, expense. And no blood or stool test matches the sensitivity of a well-performed colonoscopy. The balance between over-screening and missing disease is a clinical judgment call that guidelines are still calibrating.
What Kim’s story makes undeniable is that the current system, even when it works as designed, can miss cancer in compliant, low-risk, asymptomatic patients. Or in patients who are just not very familiar about which symptoms should raise a red flag, such as constipation. In a world with a screening-deficit by the millions, getting screened, by whatever means a patient will actually complete, may eventually matter more than which test they choose.
