Bleach sedimentation method for increased sensitivity of sputum smear microscopy: does it work?
SETTING: A non-governmental organisation (NGO) supported tuberculosis control programme in Bangladesh with good smear microscopy. OBJECTIVE: To verify whether bleach sedimentation method increases the sensitivity of sputum smear microscopy for acid-fast bacilli (AFB), and if so, how. DESIGN: Duplicate smears from successive routine specimens, peripheral centres examining direct smears, and blind examination of bleach sediment smears at central laboratories. RESULTS: When all 3,287 sputum samples were examined in duplicate and the International Union Against Tuberculosis and Lung Disease cut-off for positivity was applied, more positives were not found by bleach sedimentation. Using the much lower American Thoracic Society (ATS) threshold, the percentage positives rose slightly from 15.5% for direct smear to 16.6% after bleach. The gain was more evident when suspect examinations only were taken into consideration, as bleach missed many positives identified by direct follow-up smear. Whe
