Sputum processing methods to improve the sensitivity of smear microscopy for tuberculosis: a systematic review

Area of Science:

• Medical Diagnostics
• Microbiology
• Public Health

Background:

• Direct sputum smear microscopy is the primary tuberculosis diagnostic tool in low- and middle-income countries.
• Its main limitations include low sensitivity, particularly in HIV-coinfected individuals, and variable quality control.
• Improved sensitivity is crucial for effective tuberculosis case detection.

Purpose of the Study:

• To systematically review methods for enhancing sputum smear microscopy sensitivity.
• To compare the effectiveness of various physical and chemical sputum processing techniques.
• To assess the impact of these methods on diagnostic accuracy for pulmonary tuberculosis.

Main Methods:

• A systematic review of 83 studies was conducted.
• Studies evaluated physical (centrifugation, sedimentation) and chemical (bleach) sputum processing methods.
• Sensitivity and specificity of processed smears were compared to direct smears.

Main Results:

• Centrifugation combined with chemical methods demonstrated increased sensitivity compared to direct smears.
• Overnight sedimentation after chemical processing also showed improved sensitivity.
• Specificity remained comparable across methods; data for HIV-coinfected patients were insufficient.

Conclusions:

• Sputum processing techniques, particularly centrifugation and sedimentation, enhance microscopy sensitivity for tuberculosis diagnosis.
• Further operational studies are required to evaluate cost, complexity, biohazards, and feasibility.
• The value in HIV-coinfected populations needs additional investigation.