Sana Rehman, Rizwan Iqbal, Muhammad Kashif Munir, Arsalan Ahmad Salam, Saqib Saeed.
Incremental yield of submitting three sputum specimens for the diagnosis of pulmonary tuberculosis.
Pak J Med Res Jan ;52(2):35-8.

Objectives: To assess the efficacy and diagnostic yield of third sputum smear among pulmonary TB patients. Study type, settings and duration: This retrospective data analysis was done at PMRC TB Research Centre in collaboration with Institute of Chest Medicine, King Edward Medical University/Mayo Hospital Lahore, from January 2010 to December 2011. Materials and Methods: Patients presenting with respiratory symptoms, having abnormal chest X-rays and having a clinical suspicion of tuberculosis were asked to submit three sputum samples on two consecutive days (1stspot, 2ndearly morning, 3rdspot) for acid-fast bacilli smear microscopy. Smears were prepared and stained by Ziehl-Neelsen method. Results: A total of 7785 TB suspects submitted three sputum samples making a total of 23,355 slides for checking acid-fast bacilli using smear microcopy examinations. The smear positivity rate was 11.8%. About 12% suspects fulfilled the case definition of having one positive smear confirmed by a second smear, while, only 2.5% suspects fulfilled the case definition based on third smear in combination with first or second. A total 1164(15%) suspects had at least one positive smear; of these 896(77%) were positive in first smear, 190(16%) were negative in first smear but positive in second and 78(6.7%) were positive in third smear after two negative smears. Conclusion: Recently changed WHO criteria for examination of two sputum smears is based on evidences collected from the globe however, for Pakistan the value of third smear which picked almost 7% cases is quite significant and should still be practiced. Policy message: Checking AFB using 3 sputum smears should still be practiced in Pakistan especially, for those who are initially negative on 2 smears.

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