False negativity in AFB Smear microscopy: An insight into the caveats of the most widely used screening tool for tuberculosis.

Objective: To study the ratio of false negativity in sputum samples in diagnostic smears received for acid fast bacilli smear microscopy.

Methods: The retrospective cross-sectional study was conducted at the Ojha Institute of Chest Diseases, Karachi, and comprised specimens for microscopy and culture from presumptive tuberculosis patients for 38 months starting from November 2010.All laboratory investigations had been done as per the National Tuberculosis Control Programme guidelines.