Chlamydia pneumoniae serology: Interlaboratory variation in microimmunofluorescence assay results

The lack of standardization in chlamydia serology has made interpretation o f published data difficult. This study was initiated to determine the exten t of interlaboratory variation of microimmunofluorescence (MIF) test result s for the serodiagnosis of Chlamydia pneumoniae infections. Identical panel s of 22 sera were sent to 14 laboratories in eight countries for the determ ination of IgG and IgM antibodies by MIF Although there was extensive varia tion in the numeric titer values, the overall percentage agreement with the reference standard titers from the University of Washington was 80%. For r esults by serodiagnostic category, the best agreement was for four-fold ris e in IgG titers, while the lowest agreement was for negative or low IgG tit ers. Agreement for IgM titers was 50%-95%. Four laboratories failed to disc ern false-positive IgM titers possibly because of the presence of rheumatoi d factor. Further studies are underway to determine the source of interlabo ratory variation for the MIF test.