Value of three sputum smears microscopy in diagnosis of pulmonary tuberculosis

ABSTRACT

Early diagnosis and treatment are essential to prevent transmission of tuberculosis in the community. Smear microscopy with Zeihl-Neelsen [ZN] staining is currently the most feasible microbiological method for diagnosis of pulmonary TB in developing countries due to its rapidity, low cost and high positive predictive value for Mycobacterium tuberculosis. This study was carried out to assess the diagnostic yield of three AFB smears microscopy among suspected pulmonary tuberculosis patients of Lahore district. This descriptive study was conducted at PMRC TB Research Centre King Edward Medical University/Mayo Hospital, Lahore Pakistan where DOTS has been implemented. Patients with respiratory symptoms and or abnormal chest X-rays provided three sputum samples each for acid-fast bacilli smear microscopy. Smears were prepared and stained by Ziehl-Neelsen staining method. In 2006 a total of 2,222 TB suspects submitted three sputum samples on two consecutive days [spot, early morning, spot], therefore 6,666 AFB smear microcopy examinations were performed. The smear positivity rate was 11.5% and 257 [11.56%] suspects fulfilled the case definition of having one positive smear confirmed by a second smear. A total of 438 [19.7%] suspects had a least one positive smear; of these 290 [66.2%] were positive in first smear, 105 [24%] were negative in first smear but positive in second and 43 [9.8%] were positive in third smear after two negative smears. At least three smear microscopy examinations are required for proper diagnosis. The higher diagnostic yield of 9.8% in third smear is indicative of the importance of third smear