From the Guidelines
The positive predictive value (PPV) of Cologuard is approximately 42% for colorectal cancer detection, as reported in the most recent and highest quality study available 1. This means that about 42% of positive test results truly indicate cancer, while the remaining 58% are false positives. The PPV varies based on the prevalence of colorectal cancer in the tested population, with higher PPVs in higher-risk groups. For advanced precancerous lesions, the PPV is lower, around 20% 1. Despite this limitation, Cologuard remains a valuable non-invasive screening option with high sensitivity (92%) for detecting colorectal cancer, making it effective at ruling out disease when negative 1. The test works by detecting altered DNA and blood in stool samples that may indicate cancer or precancerous growths. Anyone with a positive Cologuard result should promptly undergo a diagnostic colonoscopy, as this is essential for definitive diagnosis and potential removal of any concerning lesions. It's worth noting that while other studies discuss the effectiveness of fecal immunochemical testing (FIT) for colorectal cancer screening 1, the question specifically asks about the PPV of Cologuard, making the 2015 study 1 the most relevant and highest quality evidence available. Key points to consider when interpreting Cologuard results include:
- High sensitivity for detecting colorectal cancer
- Moderate positive predictive value
- Need for follow-up colonoscopy after a positive test result
- Importance of considering the prevalence of colorectal cancer in the tested population when interpreting results.
From the Research
Positive Predictive Value (PPV) of Cologuard
- The PPV of Cologuard for colorectal cancer was found to be 1.3% in a retrospective review of patients referred for colonoscopy after a positive Cologuard test 2.
- The PPV for precancerous lesions plus colorectal cancer was 7.7% in the same study 2.
- A comparison of different screening tests, including Cologuard, found that the sensitivity of Cologuard for colorectal cancer was not significantly different from that of fecal immunochemical testing (FIT) when the specificity of FIT was adjusted to match that of Cologuard 3.
- A study on the cost-effectiveness of different screening tests, including Cologuard, found that Cologuard was less effective than FIT and colonoscopy in reducing colorectal cancer incidence and mortality, but could still contribute to colorectal cancer control by achieving screening in those who will not use established methods 4.
Comparison with Other Screening Tests
- A study comparing the performance of Cologuard with FIT found that FIT had a higher sensitivity for advanced neoplasia than Cologuard when the specificity of FIT was adjusted to match that of Cologuard 3.
- A study on the cost-effectiveness of different screening tests found that FIT and colonoscopy were less costly and more effective than Cologuard in reducing colorectal cancer incidence and mortality 4.
- A study on the positive predictive values of fecal immunochemical tests found that the PPV for advanced neoplasia varied by brand, and that patient factors such as female sex and history of a colorectal condition were associated with false-positive results 5.