From the Guidelines
Cologuard can produce false positive results in a significant proportion of cases, highlighting the need for follow-up colonoscopy to confirm findings. When considering the use of Cologuard for colorectal cancer screening, it is essential to weigh the benefits and harms, including the potential for false positives, as outlined in the guidance statement from the American College of Physicians 1. The test's sensitivity for detecting colorectal cancer is around 92%, but it is less accurate for detecting precancerous polyps, with a sensitivity of about 42% for advanced adenomas. Some key points to consider about Cologuard and other screening methods include:
- The American College of Physicians recommends selecting a colorectal cancer screening test based on a discussion of benefits, harms, costs, availability, frequency, and patient preferences 1.
- Fecal immunochemical testing (FIT) or high-sensitivity guaiac-based fecal occult blood testing (HSgFOBT) are suggested every 2 years, while colonoscopy is recommended every 10 years, or flexible sigmoidoscopy every 10 years plus FIT every 2 years 1.
- Cologuard, which combines FIT with stool DNA (sDNA) testing, has a higher sensitivity than FIT alone but also has lower specificity and higher false-positive rates, leading to increased harms associated with colonoscopy follow-ups 1.
- The net benefit of Cologuard compared to other screening options is uncertain due to its higher false-positive rate and the potential for overtreatment of incidental findings 1. Given these considerations, patients with a positive Cologuard result should undergo follow-up colonoscopy to confirm the presence of cancer or polyps, and those at average risk for colorectal cancer should discuss appropriate screening intervals with their healthcare provider.
From the Research
Cologuard False Positives
- The study 2 found that out of 78 patients who underwent colonoscopy after a positive Cologuard test, 53 (68.0%) had either a totally normal colonoscopy or hyperplastic polyps, and 70 (89.7%) had normal findings, hyperplastic polyps, or non-advanced adenomas.
- The positive predictive value (PPV) for colorectal cancer was 1.3%, and for precancerous lesions plus colorectal cancer was 7.7% 2.
- This suggests that Cologuard may have a high rate of false positives, as a significant proportion of patients with a positive test result did not have colorectal cancer or advanced adenomas.
- In comparison, other studies have found that fecal immunochemical tests (FITs) and flexible sigmoidoscopy have different detection rates for colorectal cancer and advanced adenomas 3, 4.
- However, these studies did not specifically examine the false positive rate of Cologuard, and more research is needed to fully understand the accuracy of this test.