JC polyomavirus (JCPyV) can cause progressive multifocal leukoencephalopathy (PML), a debilitating, often fatal brain disease in immunocompromised patients. JCPyV-seropositive multiple sclerosis (MS) patients treated with natalizumab have a 2- to 10-fold increased risk of developing PML. Therefore, JCPyV serology has been recommended for PML risk stratification. However, different antibody tests may not be equivalent. To study intra- and inter-laboratory variability, sera from 398 healthy blood donors were compared in 4 independent enzyme-linked immunoassay (ELISA) measurements generating >1592 data points. Three datasets (Basel1, Basel2, Basel3) used the same basic protocol, but different JCPyV virus-like p... More
JC polyomavirus (JCPyV) can cause progressive multifocal leukoencephalopathy (PML), a debilitating, often fatal brain disease in immunocompromised patients. JCPyV-seropositive multiple sclerosis (MS) patients treated with natalizumab have a 2- to 10-fold increased risk of developing PML. Therefore, JCPyV serology has been recommended for PML risk stratification. However, different antibody tests may not be equivalent. To study intra- and inter-laboratory variability, sera from 398 healthy blood donors were compared in 4 independent enzyme-linked immunoassay (ELISA) measurements generating >1592 data points. Three datasets (Basel1, Basel2, Basel3) used the same basic protocol, but different JCPyV virus-like particle (VLP) preparations and introduced normalization to a reference serum. The datasets were also compared with an independent method using biotinylated VLPs (Helsinki1). VLP preadsorption reducing ≥35% activity was used to identify seropositive sera. The results indicated that Basel1, Basel2, Basel3, and Helsinki1 were similar regarding overall data distribution (P=0.79) and seroprevalence (58.0%, 54.5%, 54.8%, 53.5%, respectively; P=0.95). However, intra-assay intra-laboratory comparison yielded 3.7% to 12% discordant results, most of which were close to the cut-off (0.080<OD<0.250) according to Bland-Altman analysis. Introducing normalization improved overall performance and reduced discordance. The inter-laboratory inter-assay comparison between Basel3 and Helsinki1 revealed only 15 discordant results, of which 14 (93%) were close to cut-off. Preadsorption identified specificities of 99.44% and 97.78% and sensitivities of 99.54% and 95.87% for Basel3 and Helsinki, respectively. Thus, normalization to a preferably WHO-approved reference serum, duplicate testing and preadsorption for samples around the cut-off may be necessary for reliable JCPyV-serology and PML risk stratification.
