Value of Repeated Direct Smear Sputum Examination in the Diagnosis of Pulmonary Tuberculosis

Abstract

Introduction: The examination of three sputum samples per suspect has been severely criticized from a public health viewpoint and several recent trials have documented the relative inefficiency of the third smear and the necessity for confirmation of a positive smear has also been contested. Aim: This study, undertaken in Qena, Egypt, aimed to determine the usefulness of examining the second and third direct smear microscopy (DSM) specimen in the diagnosis of pulmonary TB. Patients and methods: A retrospective study using record review at TB outpatient clinic; Qena Chest Hospital, Egypt, was done from 2010-2013. Direct smear results were collected as one of the following combinations PNN, PPP, PPN, PNP, NNP, NPP, and NPN, NNN, where N is a negative and P a positive smear. The proportion of positive, first, second and third specimen were calculated. Cases were considered positive having at least one positive smear confirmed by another positive one in the absence of sputum culture. Results: Out of 9420 recorded suspects, 719 of them were positive, so smear positivity was 7.6%. The majority of them were diagnosed from the first sample (96.4%). For only 3.6% (26 of 719), the second smear was positive and a third specimen was required (NPP) to make a definitive diagnosis of TB. No recorded isolated positive or negative smears in the third sample (NNP or PPN). Conclusions: These data indicated that, in our locality with limited financial resources, the incremental yield of a second sputum direct smear examination was low, and the third one was negligible indicating that examination of two sputum samples is enough among pulmonary TB patients. A third sample is required only as confirmatory if the second sample was positive. Smear microscopy can be substantially simplified with favourable resource implications.