CJD test evaluation

We generate reference reagents for evaluating assays intended to diagnose variant and sporadic CJD, and for screening blood for markers of variant CJD infection.  Several groups from commercial and research backgrounds are developing methods to diagnose variant CJD using blood samples.

Diagnostic assays where a positive result represents a significant impact to the life of the tested individual (for instance HIV, Hepatitis B and Hepatitis C) must meet strict performance criteria requirements under EU law as outlined in a common technical specification. This includes rigorous assessment of:

• sensitivity – the proportion of true positive samples correctly scored positive.

• specificity – the proportion of negative samples incorrectly scored positive.

These evaluations are normally performed using an abundance of known positive and negative samples. However, for variant CJD the availability of blood samples is limited both in terms of both volume and quantity. As such new alternative protocols are needed to establish assay performance. The Centre has prepared and assembled a bank of samples for the four stages of test evaluation:

• analytical sensitivity - disease associated aggregated PrPSc protein spiked into various blood components. This allows for laboratories to directly compare test sensitivity using identical samples where limits of detection are known.

• diagnostic sensitivity- initial assessments are performed using blood components from infected animals (we offer naturally infected sheep scrapie and experimentally infected sheep BSE samples respectively). This allows for laboratories to assess compatibility of test reagents with potentially problematic endogenous material. A final assessment is conducted using clinically derived vCJD blood components.

• analytical specificity- assessment of various blood components derived from the more common form of CJD (sporadic).

• diagnostic specificity- disease free blood and blood products originating from the USA, a country considered low risk for BSE.

The high quality reagents provided by the Centre for test evaluation are sourced  from groups researching human and animal TSEs and from blood services worldwide.

Access to rare samples of animal or human origin held by the CJD Research and Resource Centre is granted by the NIBSC CJD Research and Resource Centre Oversight Committee, comprised of the foremost experts on CJD from the UK and Europe.

To become a candidate for test evaluation, or to learn more about how the test evaluation process can help you, contact jillian.cooper@nibsc.org.