Acid-fast microscopy on polycarbonate membrane filter sputum sediments

Polycarbonate membrane filters were used to concentrate 916 sputum specimens for detecting acid-fast bacilli by microscopic examination. These results were compared with those of smears prepared from centrifugates and direct smears of the same specimens. Culture isolation, the control procedure, demonstrated the presence of acid-fast bacilli in 76 specimens. The number of positive specimens detected by microscopy was 82 on polycarbonate membrane filter concentrates, with an 80.2% sensitivity; 53 on centrifugate smears, with a 62.2% sensitivity; and 44 on direct smears, with a 55.8% sensitivity. Acid-fast microscopy results demonstrated that the sensitivity of the polycarbonate membrane filter sputum concentration method was superior to that of the recommended centrifuge concentration method and that the former method may be considered a rapid alternative when culture for acid-fast bacilli is impractical.