From the Research
The false negative rate for colon cancer screening using CT colonography is approximately 6.7%. This means that CT colonography may miss around 6.7% of significant colorectal lesions or cancers that are actually present. The false negative rate varies depending on several factors including the size of the lesions, with CT colonography being more accurate for detecting larger polyps (≥10 mm) than smaller ones. Technical factors such as bowel preparation quality, imaging technique, and the radiologist's experience also significantly impact detection rates. CT colonography is generally better at detecting polyps in the distal colon compared to the proximal colon. For context, traditional optical colonoscopy, which remains the gold standard, has a lower false negative rate of approximately 2-6% for significant lesions, as seen in a study where the false negative rate for colonoscopy was 3.5% 1. Patients should understand that while CT colonography is less invasive than conventional colonoscopy, it does have limitations in detecting smaller lesions and flat polyps, which contributes to its higher false negative rate.
Some of the key factors that influence the false negative rate of CT colonography include:
- Size of the lesions: CT colonography is more accurate for detecting larger polyps (≥10 mm) than smaller ones
- Technical factors: bowel preparation quality, imaging technique, and the radiologist's experience significantly impact detection rates
- Location of the polyps: CT colonography is generally better at detecting polyps in the distal colon compared to the proximal colon
It's worth noting that the false negative rate of CT colonography can be improved with advancements in technology and techniques, such as the use of primary three-dimensional review methods and the addition of oral contrast agents to bowel preparation, as discussed in a study from 2005 2. However, the most recent and highest quality study available, from 2015, reports a false negative rate of 6.7% for CT colonography 1.
In real-life clinical practice, it's essential to consider the potential false negative rate of CT colonography and weigh it against the benefits of the screening method, including its less invasive nature and lower risk of complications compared to traditional colonoscopy. Patients should be informed about the potential limitations of CT colonography and the importance of follow-up screening and diagnostic testing if symptoms persist or if a false negative result is suspected.