Same-day sputum smear microscopy for the diagnosis of pulmonary tuberculosis: direct vs. concentrated smear

To evaluate the efficacy of sputum microscopy by the concentration method using spot and morning and same-day smears for the diagnosis of pulmonary tuberculosis.

Three sputum specimens (spot, second spot and morning) were collected from study participants. Three smears were prepared from the direct sample and three using the N-acetyl-l-cysteine-sodium hydroxide concentration method. The smears were stained using Ziehl-Neelsen (ZN) staining, modified ZN (MZN) staining and fluorescent staining (FS). Smear results were pooled and compared in two categories: standard spot and morning, and same-day smears. The χ(2) test was used to evaluate the statistical difference in smear-positive cases.

Among 3186 participants included in the study, smear positivity was respectively 9.6%, 9.8% and 10.8% for ZN, MZN and FS smears using spot and morning smears. Using same-day smears, smear positivity was respectively 9.5%, 9.8% and 10.6% for ZN, MZN and FS smears. Smear positivity increased to 16% with the concentration method.

Nil dropouts and patient convenience are the added advantages of using same-day smears, and the concentration method improved smear positivity. Given these advantages, using same-day smears with the concentration method should be considered by the World Health Organization and India's Revised National Tuberculosis Control Programme.