45/47 kilodalton (APA) antigen capture and antibody detection assays for the diagnosis of tuberculosis

SETTING: APA complex (45/47 kDa) is an antigen specifically excreted by Myc obacterium tuberculosis and could therefore be a good candidate for diagnos is. OBJECTIVES: TO develop three APA immunocapture ELISA assays using monoclona l antibodies (Mabs) and one IgG anti-APA ELISA test, and to determine their usefulness for the diagnosis of tuberculosis in Madagascar. DESIGN: For the Ag assays, 23 negative sputum and serum samples and 64 pair s of sputum and serum from active smear-positive patients (PTM+) were teste d. For antibody assay, 116 negative controls, 143 PTM+ and 54 extra-pulmona ry tuberculosis patients were tested. RESULTS: The sensitivities of the APA antigen detection assays were low (le ss than 40%) for a specificity of 95.6%, using either monoclonal antibodies or clinical specimens. The anti-APA serology was more sensitive (76.9% for PTM+ patients) but less specific (73.2%). Due to their poor predictive val ues, these tests cannot be recommended for the routine diagnosis of tubercu losis in Madagascar.