Comparison of passive particle agglutination test and ELISA determination of antibody isotype on Mycoplasma pneumonia infection

Objective To investigate the consistency between the results of passive particle agglutination test (PPA) and ELISA on Mycoplasma pneumonia (M.pneumonia) infection.Study the diagnostic value of both assays. Methods From November 2010 to May 2011, the serum samples of ］191 patients with respiratory symptoms were collected from Affiliated Hospital of Jining Medical University.All samples were tested for antibody levels against M.pneumonia using PPA, and for IgM, IgG, IgA subclass using ELISA.The correlation between the results of two methods was evaluated by Kappa test and Spearman rank correlation analysis.The variances of the antibody subclasses among samples with different PPA titers and different age groups were analyzed by Kruskal-Wallis test.The infection status of patients was analyzed based on ELISA results and the clinical relevance of both assays was evaluated in comparison with clinical diagnosis for samples with high PPA titer. Results The level of agreement between the results of PPA and ELISA was 84.3%, with Kappa value of 0.642 (P<0.01).The prevalence of IgM and IgA antibody against M.pneumonia was significantly different among samples with various PPA titers (P<0.05).The prevalence of IgM subclass was higher in child and teenager groups, while that of IgA and IgG were higher in elderly group.Antibody isotyping results suggested that 58.1% of PPA positive samples (75 cases), especially 96.4% of samples with high PPA titer (27 cases), were of current infection, which was in consistent with clinical diagnosis. Conclusion PPA showed good consistency with ELISA on diagnosis of Mycoplasma pneumonia infection.Antibody subclass determination by ELISA indicates disease progression, thus to differentiate current infection from past.（Chin J Lab Med，2012,35：639-642） Key words: Mycoplasma pneumonia; Agglutination tests; Immunoglobulin M; Immunoglobulin G; Immunoglobulin A