Aims: This study evaluates the use of local B. burgdorferi sensu stricto and B. afzelii strains in a single mixed antigen for in-house IgG Western blots in the routine diagnostic setting, by comparing it with our current protocol.
Methods: Sera from 233 patients from low and high prevalence areas of Scotland 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 compared.
Results: The mixed antigen produced significantly more bands than the reference antigen. Using the original interpretation criteria the mixed antigen produced more positives than the reference antigen (90 vs 85). When the revised criteria was applied to the mixed antigen there were 14 more positive patients than with the reference antigen (99 vs 85), this difference was significant. Although 22 patients were positive with the mixed antigen and revised criteria, but negative/ equivocal with the reference antigen, 8 reference antigen positive patients remained negative with the mixed antigen. The positive predictive value of both antigen preparations was the same (96%). The negative predictive value of the mixed antigen with revised criteria was higher than the reference antigen (96 vs 88%), but the specificity was similar (97 vs 98%).
Conclusions: The mixed antigen and revised interpretation criteria has successfully been incorporated into the routine diagnostic testing service, increasing the sensitivity of the in-house IgG Western blot test for Scottish patients.