Comparison of direct versus concentrated smear microscopy in detection of pulmonary tuberculosis

BMC Research Notes

Sayera Banu²  Frank van Leth¹  Razia Khatun²  Md Toufiq Rahman²  Shahriar Ahmed²  Md Raihan Chowdhury²  Mohammad Khaja Mafij Uddin² 

[1] Department of Global Health, Amsterdam Institute for Global Health and Development, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands;International Centre for Diarrhoeal Disease Research, Bangladesh

关键词: Sputum smear microscopy;    Direct vs. Concentrated smear microscopy;    Sensitivity;    Tuberculosis;   

Others  :  1142059
DOI  :  10.1186/1756-0500-6-291

 received in 2012-11-01, accepted in 2013-07-23,  发布年份 2013

【 摘 要 】

Background

Sputum smear microscopy is fast and inexpensive technique for detecting tuberculosis (TB) in high incidence areas but has low sensitivity. Physical and chemical sputum processing along with centrifugation have been found to show promise in overcoming this limitation. Our objective was to compare the sensitivity of smear microscopy obtained with smears made directly from respiratory specimens to those from concentrated specimens.

Methods

By active screening, 915 TB suspects were identified from Dhaka Central Jail and sputum specimens were aseptically collected. Direct smears were prepared by taking a small portion of the purulent part of the sputum with a sterile loop. The specimens were then processed by a standard N-acetyl-L-cysteine-NaOH digestion-decontamination method to prepare concentrated specimens. Both smears were then air dried, heat fixed, and stained by the Ziehl-Neelsen staining technique. The stained slides were examined under oil immersion and were graded following International Union Against Tuberculosis and Lung Diseases guidelines. All the specimens were inoculated into Lowenstein-Jensen (L-J) media and culture results were considered as gold standard to calculate sensitivity.

Results

Of 915 specimens, 73 (8%) specimens were positive both on direct and concentrated methods, one sample was positive on direct microscopy but was negative on concentrated method. An extra 14 (1.5%) samples were positive on concentrated method which were negative on direct smear. In L-J media 105 specimens were found positive for TB bacilli and of them, 74 (70.5%) and 87 (82.9%) were positive in direct and concentrated smear, respectively. The sensitivity of direct and concentrated smear microscopy was different when using positive culture as the gold standard (71% vs. 83%).

Conclusions

The results showed that concentrated technique increases the sensitivity of microscopy up to 12%. Therefore, the national programs in high TB burden countries may consider incorporating the technique into their guidelines at least in the district and higher level laboratories to improve case finding strategy.

【 授权许可】

   
2013 Uddin et al.; licensee BioMed Central Ltd.

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