Incremental yield of submitting three sputum specimens for the diagnosis of pulmonary tuberculosis

ABSTRACT

To assess the efficacy and diagnostic yield of third sputum smear among pulmonary TB patients. 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. 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 [1[st]spot, 2[nd]early morning, 3[rd]spot] for acid-fast bacilli smear microscopy. Smears were prepared and stained by Ziehl-Neelsen method. 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. 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. Checking AFB using 3 sputum smears should still be practiced in Pakistan especially, for those who are initially negative on 2 smears