Thousands of patients across the State may need to have their medical tests redone after a major flaw was identified in the Health Service Executive’s (HSE) computer systems.

Others may have received unnecessary treatment as a result of faulty information on the HSE’s system for storing scans electronically.

At least 25,000 X-rays, MRIs, CTs and ultrasounds taken since 2011 are affected by the error, which was discovered only last week.

The HSE says it does not know to what extent patients may be affected, but a major investigation is now under way to establish the extent of the issue.

The problem has arisen with images of patients’ tests held at the HSE’s National Integrated Medical Imaging System (NIMIS), which is used to store radiology, cardiology and other diagnostic images electronically.

It has been discovered that when images are archived, the “less than” symbol, “<”, when used in a report, was omitted and is not visible.

This would mean that, for example, where a patient had stenosis (narrowing) of the arteries of <50 per cent, this would be recorded wrongly as 50 per cent. The radiologist who wrote the original report would remain unaware of the error.

One radiologist said some patients could have been treated unnecessarily as a result of their symptoms appearing worse than they were.

System ‘glitch’

The HSE’s national clinical adviser for acute hospitals, Dr Colm Henry, described the issue as a “glitch”. He said it was “unlikely” to have led to patients suffering serious clinical harm or being treated inappropriately.

A review of other keyboard symbols used in medical imaging reports has found the problem was confined to the “less than” symbol, he said.

“The quality of radiology is not affected. In addition, clinical decisions on a patient are rarely based nowadays on a written report or single X-ray alone. For important decisions, doctors looking at reports will usually verify by other means, usually by looking at the scans themselves,” he said.

The HSE has convened a serious incident management team to assess the risk to patients as a result of the error. It is examining a representative sample of 10 per cent of the affected scans to see if a further clinical review is required.

If this initial investigation shows a higher than expected number of affected patients, a more comprehensive review would be carried out, Dr Henry said.

An investigation is also under way to see if pre-2011 scans that were migrated to the NIMIS system are affected.

The error was spotted by a radiologist working in a provincial hospital last Friday, and escalated to HSE headquarters. A patch was applied to the NIMIS system, by replacing the “<” with the words “less than”.

“The system has been checked and no new issues have been created since 7pm on Thursday, July 27th,” according to a statement from the HSE.

It said reports reviewed on paper, and those sent electronically to GP practices, were not affected by the issue.

All hospitals and radiology departments operating the NIMIS system have been notified of the problem and will be asked to examine affected records.

The €40 million NIMIS system was introduced to replace traditional film records of patients’ scans with electronic images that can be shared between different treating doctors and hospitals. The rollout of the programme was subject to major delays but most hospitals are now connected to the system.