EVALUATION OF MODIFIED CYTOSPIN SLIDE MICROSCOPY FOR DETECTION OF ACID FAST BACILLI IN BRONCHOALVEOLAR LAVAGE FLUID FOR DIAGNOSIS OF PULMONARY TUBERCULOSIS

Abstract

Objective: To evaluate the cytospin slide microscopy method for detection of acid fast bacilli (AFB) in bronchoalveolar lavage (BAL) fluid comparing it with concentrated smear microscopy.

Study Design: Cross-sectional validation study.

Place and Duration of Study: Department of Microbiology, Armed Forces Institute of Pathology (AFIP), Rawalpindi, from Dec 2016 to Sep 2018.

Methodology: BAL specimens from suspected tuberculosis patients who were sputum smear negative, submitted to AFIP for diagnosis were included in the study. Smears for microscopy were prepared with the modified cytospin method as well as the standard concentrated technique. The prepared smears from both methods were stained with Ziehl–Neelsen (ZN) staining method and examined under 100 × oil immersion lens. TB culture performed on BACTEC MGIT 960 automated culture system (Becton Dickinson, USA) was taken as gold standard for TB diagnosis. The two methods were compared in terms of sensitivity, specificity, positive predictive value and negative predictive value.

Results: Out of the 130 samples tested, 62 (47.7%) were positive on culture using MGIT 960 system. The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of the modified cytospin method for pulmonary TB diagnosis was found to be 68.3%, 100%, 100%, 77% and 84.6%, respectively.

Conclusion: The sensitivity of the modified cytopsin smear method was significantly higher than that of the concentrated method. The study concludes that this is a simpler and more accurate method for BAL fluid microscopy.