oa African Journal of Laboratory Medicine - Improved sensitivity, safety and laboratory turnaround time in the diagnosis of pulmonary tuberculosis by use of bleach sedimentation : original research

Volume 4, Issue 1
  • ISSN : 2225-2002
  • E-ISSN: 2225-2010



Inadequate diagnostic processes and human resources in laboratories contribute to a high burden of tuberculosis (TB) in low- and middle-income countries. Direct smear microscopy is relied on for TB diagnosis; however, sensitivity rates vary. To improve sensitivity of direct microscopy, the researchers employed several approaches, including sputum digestion and concentration of acid-fast bacilli (AFB), a technique which uses commercial bleach.

This study compared methods used to diagnose active Mycobacterium tuberculosis infections.
Three sputum specimens were collected from each of 340 participants in Abuja,Nigeria, over two consecutive days. Direct microscopy was performed on all specimens; following microscopy, one specimen from each patient was selected randomly for bleach sedimentation and one for Lowenstein-Jensen culture.
Direct microscopy produced 28.8% AFB-positive results, whilst bleach sedimentation resulted in 30.3%. When compared with the cultures, 26.5% were AFB true positive using direct microscopy and 27.1% using bleach sedimentation. Whilst the specificity rate between these two methods was not statistically significant ( = 0.548), the sensitivity rate was significant ( = 0.004).
Based on these results, bleach increases the sensitivity of microscopy compared with direct smear and has similar specificity. When diagnosing new cases of pulmonary TB, one bleach-digested smear is as sensitive as three direct smears, reducing waiting times for patients and ensuring the safety of laboratory technicians.

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