Evaluation of a passive hemagglutination assay as screening test and of a recombinant immunoblot as confirmatory test for serological diagnosis of Lyme disease.

In order to evaluate a commercially available passive hemagglutination assay (PHA) as a screening test for the diagnosis of Lyme disease, 173 sera were tested by PHA and the results compared with those obtained by an indirect immunofluorescence assay (IFA) and a conventional immunoblot using whole cell antigen (IB). Identical results were found by PHA and IFA in 80% of all cases. The sensitivity of the PHA was comparable to that of the IB (96%). However, confirmation of positive PHA results was necessary due to lack of specificity. A commercially available recombinant immunoblot (RIB) was compared to a conventional IB for its efficiency as a confirmatory assay. The rate of agreement was 86% of 64 sera tested positive or negative by IB. However, in order to obtain this high concordance of the RIB and IB, it was necessary to modify the RIB interpretation criteria of the manufacturer. Thus, screening of serum specimens by the PHA and confirmation of test results by the RIB appears to be a convenient test combination that allows the serological diagnosis of Lyme disease in most cases.