Local Borrelia burgdorferi sensu stricto and Borrelia afzelii strains in a single mixed antigen improves Western blot sensitivity.

Aims: This study evaluates the use of local Borrelia burgdorferi sensu stricto and Borrelia afzelii strains in a single mixed antigen for in-house IgG western blots in the routine diagnostic setting by comparing it with the current in-house protocol. Methods: Sera from 233 patients from areas of Scotland with low and high prevalence for Lyme borreliosis were tested by western blots prepared from reference strain antigen (B burgdorferi sensu stricto) and mixed antigen (B burgdorferi sensu stricto and B afzelii). Results were scored using original and revised criteria, and results were compared. Results: The mixed antigen produced significantly more bands than the reference antigen. Using the original interpretation criteria the mixed antigen produced more positive results than the reference antigen (90 versus 85). When the revised criteria were applied to the mixed antigen there were 14 more patients with positive results than with the reference antigen (99 versus 85); this difference was significant. Although 22 patients were positive with the mixed antigen and revised criteria, but negative/equivocal with the reference antigen, eight patients who were positive with reference antigen remained negative with the mixed antigen. The positive predictive value of the two antigen preparations was the same (96%). The negative predictive value of the mixed antigen with revised criteria was higher than the reference antigen (96% versus 88%), but the specificity was similar (97% versus 98%). Conclusions: The mixed antigen and revised interpretation criteria have been successfully incorporated into the routine diagnostic testing service, increasing the sensitivity of the in-house IgG western blot test for Scottish patients.