Fluorescence polarization assay for the diagnosis of bovine brucellosis: adaptation to field use

Abstract A fluorescence polarization assay (FPA) was used to test whole blood samples prepared by mixing blood cells from cattle without exposure to Brucella abortus ( B. abortus ) with sera from animals with confirmed (bacteriologically) infection. A cut-off value between negative and positive values was initially established to be 87.2 mP. This value was changed to 95 mP to increase assay specificity without loss of sensitivity when testing blood samples from negative animals. The FPA technology was applied to whole blood samples in the field and to stored whole blood samples using two diluent buffers. Relative sensitivity and specificity values for the FPA performed in the field, based on buffered antigen plate agglutination test and competitive enzyme immunoassay results were 95.3 and 97.3%, respectively. However, to obtain maximum sensitivity and specificity, a cut-off value of 105 mP was determined for fresh whole blood samples. The relative sensitivity and specificity values of the FPA when testing stored whole blood samples were 100% each using a 95 mP cut-off. The usefulness of the FPA for testing whole blood samples in the field was demonstrated.