Enhanced ELISA for detection of anti-JC virus antibodies in MSers
Biogen Idec, the company that markets natalizumab, has introduced an improved STRATIFY JCV assay, called STRATIFY DxSelect. This second generation test has an improved ability to detect seropositivity in samples with low levels of anti-JCV antibodies; it should minimises the occurrence of false negative results. It is anticipated that approximately 5-10% of MSers with very low anti-JCV antibody levels who tested negative using first generation STRATIFY JCV test may test positive with STRATIFY DxSelect. As a result, there may be an increase in the number of MSers who had previously tested anti-JCV antibody negative prior to March 2012 now test anti-JCV antibody positive at a rate above what might be expected from the scientific literature. Over time, once MSers have been tested with STRATIFY JCV DxSelect, we expect the rate of MSers changing serostatus to stabilise.
“This may affect a handful of MSers on natalizumab who have already tested negative with the first assay. Please be prepared that if your first test was negative the second may be positive due to the better performance of the assay or you may have been exposed to the virus, and seroconverted, between tests.”