US President Barack Obama has reportedly undergone CT colonography, a screening tool to detect colorectal cancer, as part of his annual physical examination (www.clinica.co.uk, 4 March 2010).

This begs the question of why the procedure, also known as virtual colonoscopy, is not covered by Medicare in the US. If it's good enough for the president, then why not for the general public?

The decision not to reimburse CT colonography, taken last May, was met with anger in some quarters (www.clinica.co.uk, 15 May 2009). The Centers for Medicare and Medicaid Services said at the time that there was not enough evidence to support covering its costs, but the American Cancer Society argued that randomised clinical trials have shown it to be as effective as traditional optical colonoscopy for detecting early cases of colorectal cancer and precancerous polyps.

The president's decision to pick the more convenient, more expensive technique that is denied to uninsured Americans is likely to stoke this anger.

CT colonography has obvious advantages over conventional optical colonoscopy, which involves a camera on a flexible tube being inserted into the intestine via the anus. It is widely acknowledged that the invasive nature of the test is a major reason why many people currently forgo screening.

Virtual colonoscopy, which reconstructs images of the intestine from an abdominal CT scan, is a patient-friendly alternative that could encourage more people to attend screening. It is also safer for elderly patients, who are more likely to suffer complications such as bowel perforation during optical colonoscopy, and does not require sedation, unlike the traditional technique.

The main argument has therefore been over whether the virtual method is as effective at detecting colon cancer as the optical technique. And Obama's decision speaks volumes. Would the president, after talking to his doctors and advisors, have opted for the test if there were serious doubts over its efficacy? Surely that would not be allowed to happen.