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Bleach sedimentation method for increased sensitivity of sputum smear microscopy: does it work?
A Van Deun1, A K Maug, E Cooreman
1Mycobacteriology Unit, Institute of Tropical Medicine, Antwerpen, Belgium. avdeun@microbiol.itg.be
Summary
The bleach sedimentation method offers a minor increase in detecting tuberculosis (TB) via sputum smear microscopy, particularly for borderline cases. However, it requires careful implementation to avoid false results and manage the increased workload.
Area of Science:
- Microbiology
- Infectious Diseases
- Public Health
Background:
- Tuberculosis (TB) diagnosis relies heavily on sputum smear microscopy.
- Optimizing diagnostic sensitivity is crucial for effective TB control programs.
- The bleach sedimentation method is proposed to enhance AFB detection in sputum samples.
Purpose of the Study:
- To evaluate the efficacy of the bleach sedimentation method in increasing the sensitivity of sputum smear microscopy for acid-fast bacilli (AFB).
- To understand the mechanism by which bleach sedimentation might improve AFB detection.
Main Methods:
- A non-governmental organization (NGO)-supported TB control program in Bangladesh utilized the method.
- Duplicate smears from routine sputum specimens were examined.
- Peripheral centers performed direct smear microscopy, while central labs conducted blind examination of bleach sediment smears.
Main Results:
- Using the International Union Against Tuberculosis and Lung Disease (IUATLD) cut-off, bleach sedimentation did not increase positivity rates.
- At the lower American Thoracic Society (ATS) threshold, positivity increased slightly from 15.5% to 16.6%.
- Patient-based detection showed an average gain of 10% (range 6-16%), but with significant inter-center variability.
Conclusions:
- Bleach sedimentation can marginally improve diagnostic yield when other factors are already optimized.
- The method is not a universal solution and requires precautions against false positives and negatives.
- The additional workload associated with bleach sedimentation is a significant consideration.