The screening process for the brain condition is not completely reliable and can lead to people being wrongly told they are suffering from variant Creutzfeldt-Jakob disease (vCJD).

The test, carried out on samples of body tissue, looks for abnormal proteins known as prions which kill off brain cells and are thought to cause the disease. But researchers at Edinburgh University have now come up with a way of confirming whether someone has fatal levels of the proteins.

The technique, known as protein misfolding cyclic amplification (PMCA), works by boosting the replication of prions so they are more easily detected in test samples.

This is done by exposing the sample to repeated rounds of ultrasound, which break the prions up into more numerous smaller particles.

Further research is needed to establish whether the technique, which has been applied to brain tissue, can be applied to other tissues, such as blood, that might be used in tests for vCJD.

Professor James Ironside said: "While this method, due to the length of time it takes to carry out, is unlikely to produce a rapid screening test that could be implemented in blood donation centres, it may well be suitable as a confirmatory test that could be conducted at a national centre."

Prof Ironside, of the National CJD Surveillance Unit at the University of Edinburgh, said: "One of the issues common to screening tests is that of 'false' positive results.

"By developing a reliable confirmatory test, such as this one, the impact of these false positives can be minimised."

There have been 161 deaths from variant CJD since the disease emerged in early 1990. The figure includes three people who received blood transfusions from donors who later developed the disease.