Patients' lives could be being put at risk because one in 10 scan results are not reported to doctors, a report by the healthcare watchdog warns today.

The Healthcare Commission found that the results of almost 10% of diagnostic scans - including x-rays, ultrasounds and MRI or CT scans - are never formally reported to the clinicians who order them.

In some cases there will be an agreement that an x-ray is fine if no written result is offered; in others, doctors may have been told the results informally. Clinicians may also look at scans and reach their own conclusions. But such an approach risks leaving injuries or serious conditions undetected - particularly when scans have been ordered by GPs, who will not normally be able to view the images, or by relatively- inexperienced A&E doctors.

"The fact that the results from 10% of imaging examinations are never formally reported means that injuries and serious conditions can go undetected, and this potentially puts patients at risk," said Anna Walker, chief executive of the Healthcare Commission.

The study, An Improving Picture? Imaging Services in Acute and Specialist Trusts, covered all 196 imaging departments in England. It found most had significantly reduced their waiting times for diagnostic tests between 2001 and 2005, when the survey was conducted. Average waiting times for a non-urgent CT scan had dropped from seven to five weeks, and for an MRI scan from 21 weeks to 14 weeks.