The biggest issue with colorectal cancer screening is not determining which test should be performed, but that too many individuals do not have any test performed at all. Less than half of adults over 50 have had a test within the recommended time frames. However, you've hit upon a pretty hotly debated subject with new information coming in all the time.
To answer your question, we must first establish that we are talking about a screening for a person with average risk of colon cancer. If the test is being performed on a higher risk person or used as a diagnostic tool (for example, to evaluate a symptom), the issues to consider might change.
For those who may not be familiar with the differences between the screenings, here's a definition of each. A "virtual colonoscopy" is a CT (computed tomography) scan where the images are reconstructed on a computer to create a 3-D image that visually simulates a colonoscopy. A traditional colonoscopy is done with a flexible tube with channels through which biopsy forceps and other tiny surgical instruments can be passed. It uses fiber-optics and a camera to show the colon's interior lining where polyps and cancers may lurk.
When choosing between a traditional and a virtual colonoscopy, the main factors to consider are the ability of the tests to find a cancer or pre-cancerous polyp, the risks of the tests, and the cost effectiveness of the tests. Patient preferences also matter.
Both colonoscopy methods are fairly good at finding cancers or polyps that may become cancers. Neither is perfect, but both methods are getting better. Traditional colonoscopy has the edge and the longer track record, however.
Both tests are safe. Perforation of the intestine or bleeding can occur with either, but is very rare in a screening test (as compared to an emergency colonoscopy). Both procedures require an extensive clean out of the colon with laxatives beforehand. Either can be done with or without sedation, but the virtual colonoscopy is usually performed without sedation, while the traditional colonoscopy is usually done with it. When conducting a cost benefit analysis of the two procedures using typical costs, the better buy for society is the traditional colonoscopy. Meanwhile, patient preference varies, and there are no clear trends.
It's important to note that a virtual colonoscopy can only detect abnormalities, like a mammogram does for breast cancer. We think a lot of cancers begin as polyps. During a traditional colonoscopy, any polyps found can be removed and sent to the lab. So, traditional colonoscopy is both a test and a treatment (potentially). It does not just detect cancer, but may help prevent it as well.
Although I'm not your doctor, I'll say what I tell my patients when I recommend the traditional colonoscopy. It has a great history of success, while virtual colonoscopy is pretty new and not done well by everyone yet. And—here's the clincher—if a virtual colonoscopy finds something, you have to have a traditional colonoscopy performed. Getting the job done the first time seems preferable to me. But, whatever you and your doctor decide, get your screening. A life lost to colon cancer is a mostly preventable tragedy.
