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Blood test good enough to screen for vCJD

Assay picked up 71% of true cases – without a single false-negative result

Louise Prime

Tuesday, 04 March 2014

A blood test for variant Creutzfeldt-Jakob disease (vCJD) is sufficiently reliable to be used to screen at-risk populations for the fatal neurological disease, shows UK research. Authors of the study, published today in JAMA Neurology, suggest that the test could now be used to screen a large sample of the UK population, to estimate the proportion carrying prions in their blood – up to 3 million cattle in the UK may have been infected with bovine spongiform encephalopathy, and eating infected beef is the most common way of contracting vCJD.

Researchers led from University College London had already developed an assay to detect low blood concentrations of prions. In this study, funded by the Medical Research Council, they assessed its usefulness for large-scale screening by testing it on blood samples from various groups of people. These included 5000 healthy blood donors from the US, and 200 from the UK; 352 people with non-prion neurodegenerative disease; 105 people thought likely to have a diagnosis of prion disease; and 10 patients with confirmed vCJD.

The assay was shown to have 100% specificity – it didn’t identify a single false-positive among the samples from healthy blood donors. The study authors said: “The lack of cross-reactivity and false positives in a range of non-prion neurodegenerative diseases supports the use of the assay in patient diagnosis.”

In addition, the assay had high sensitivity – it picked up 71.4% of true cases of vCJD. The authors said the results show that their assay is sufficiently accurate to screen prion-exposed populations for vCJD in order to accurately establish its prevalence.

They concluded: “Most importantly, the prototype vCJD assay has sufficient performance to justify now screening a large UK population sample and at-risk groups to produce an initial estimate of the level of prionaemia in the UK blood donor population … A blood prevalence study would provide essential information for policy makers for deciding if routine vCJD screening is needed for blood, tissue, and organ donations and patients prior to high-risk surgical procedures.”

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