Donors can carry disease, but standard screening will miss it

She said: "If somebody has only been very recently infected (with these viruses) it may not show up in a test.

"After infection, the body starts to react against the virus and builds up antibodies to fight it. Our tests look for the antibodies. So if you're only infected a week ago, it might not have shown up yet."

She said that in reality it was very rare that this happens.

Hepatitis C infections are the most likely to slip through, as it takes the body a relatively long time to start producing antibodies for the condition - up to 60 days.

However, there has only been one case of HIV slipping through the screening programme in 11 years, she said.

This was particularly rare when the amount of blood collected and used is taken into consideration - the service collects 10,000 units of blood every day.

The typical donor would contribute one unit (450ml) in a session, and would attend two to three sessions a year.

Genetic technique

The Lancet study indicates that the genetic method could prevent infected samples making it through the screening process.

Thoroughly screened blood can be sent for use quickly

Dr Willi Kurt Roth and colleagues from Frankfurt am Main, Germany, studied the use of polymerase chain reaction (PCR) tests in blood samples taken from blood donated by 373,423 people.

PCRs are used to study genetic material. A short piece of DNA or RNA, the body's genetic blueprints, can be amplified more than 1bn times.

Using the technique they were able to test 3,000 samples a day, and testing was completed within eight hours.

They found two samples that carried the hepatitis C virus that would have been missed using standard screening methods.

The researchers concluded: "PCR is a suitable and fast blood-donor screening procedure and contributes to a reduction in viral transmission by transfusion of blood components."

Implementing the technology

Ms Murchie said the National Blood Service already has plans to implement the technology in the UK.

The service will introduce PCR screening for hepatitis C, as that is the virus that has most chance of getting through.

There are then plans to expand it to hepatitis B and HIV, although Ms Murchie warned that it was more expensive than standard methods.

"It's going to be a challenge to get it in for everything, but within the next year we should have it in for hepatitis C and follow on with the other tests as well," she said.

"Any sort of tests or new technology that can improve the safety of blood are very welcome, but I'm afraid it takes a little time to get them through," she added.