Kim Turner at the hospital with her daughter
Kim Turner
It’s 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 colorectal cancer symptom education and screening guidelines exist, patients still struggle to understand and access screening tools.
Colonoscopy remains the gold standard, but completion requires bowel preparation, 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 receive a clear colonoscopy result call for patients to return in up to 10 years for a repeat colonoscopy.
This 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. He 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 held a health fair and proposed a blood-based colon cancer screening test called Shield, from Guardant Health. Kim casually agreed. “I didn’t expect it to come back positive,” he said. However, it wasn’t until she was 61, 3 years before her screening colonoscopy, that the blood test came back positive.
A follow-up colonoscopy confirmed adenocarcinoma in a three-centimeter segment of her sigmoid colon. He 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 colon cancer, although in Kim’s case it was quite subtle, and she explained quite convincingly, that it never raised a red flag. “I had virtually no symptoms,” he said. “I was shocked.”
Shortly after diagnosis she underwent surgery to remove the cancerous mass along with 28 lymph nodes, one of which was positive. This, 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.
It was three years since her ten-year screening and the only mild, intermittent symptom she had attributed to another medical condition.
“If I had waited three years,” he said, “a very different story. Very different.”
How does the Shield test affect colon cancer screening?
In a clinical trial with more than 20,000 participants, it demonstrated 83% sensitivity for colon cancer and 90% specificity, placing it within the range of other recognized non-colonoscopy screening options.
The company recommends testing every three years and is currently covered by Medicare. Dr. Craig Eagle, the former Chief Medical Officer at Guardant Health, explains the test simply: when a colon tumor is present, it constantly sheds tiny fragments of its DNA into the bloodstream. Shield analyzes a blood sample for these fragments, looking for cancer-specific patterns. This is a test that can be ordered by a primary care physician as an outpatient.
Eagle wants to set the right expectations about using Shield in patient care. It clearly states that Shield is not a substitute for colonoscopy, “colonoscopy remains the gold standard.” Also, a positive result with Shield still requires a follow-up colonoscopy. What stands out, however, is that it offers a lower-friction option for the millions who haven’t completed a colonoscopy on schedule for a variety of reasons: fear, access, scheduling, cost. “We have the best test available to everyone, the colonoscopy, and only 20 to 40 percent of people 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 the blood-based test as a screening option, although they classify it as secondary to colonoscopy and stool tests. The FDA label uses stronger language, identifying Shield as a first-line indicated option. This gap in recommendations reflects a genuine clinical debate in which the field is still working.
As a physician myself, I still tell patients to prioritize colonoscopy, but if they refuse the more invasive test, a complementary blood test, such as Shield, or a stool-based test, such as Cologuard or ColoSense, should be discussed.
What is less clear is whether there is a role for these less invasive tests to be used between longer colonoscopy screening periods, to ensure that no disease has progressed while preserving the resources needed for colonoscopies.
Limitations around Shield testing
Like any medical exam, you need to know what is best for the patient in front of you. Shield lists two key disclaimers on its website.
1. Shield has limited detection (55%-65%) of Stage I colon cancer and misses 87% of precancerous lesions. One in 10 patients with a negative Shield result may have precancerous cancer that would have been detected by a screening colonoscopy. Shield showed high detection of stage II, III and IV colon cancer.
2. The Shield test is not indicated for patients who have a personal history of colon cancer, adenomas, or other related cancers. or who have had a positive result on another colon cancer screening method in the past six months, have been diagnosed with a condition associated with a high risk for colon cancer, such as inflammatory bowel disease (IBD), chronic ulcerative colitis (CUC), Crohn’s disease. or who have a family history of colon cancer or certain inherited 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 to how it can be used and how the results can be interpreted.
Colorectal cancer symptom education and screening guidelines
Kim 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 that patients increasingly want the medical community to answer. Is a ten-year screening interval too long, especially for patients with a previous history of polyps? And for the tens of millions who won’t complete a colonoscopy for whatever reason, do simpler less invasive tools like blood tests, stool kits deserve a more prominent place in the standard algorithm?
Currently, there is no official answer and much to consider regarding simpler less invasive tools. False positives have real costs: unnecessary procedures, stress, expense. And no blood or stool test can match the sensitivity of a well-performed colonoscopy. The balance between overscreening and obliterated disease is a clinical judgment call that guidelines are still being calibrated.
What Kim’s story makes undeniable is that the current system, even when working as designed, can miss cancer in compliant, low-risk, asymptomatic patients. Or in patients who are just not very familiar with symptoms that should raise a red flag, such as constipation. In a world with a screening deficit of millions, screening, by whatever means a patient completes, may ultimately matter more than which test they choose.
