Diagnosis of pulmonary tuberculosis by smear microscopy and culture in a tertiary health care facility

Smear microscopy and culture forms the backbone of tuberculosis (TB) laboratory investigations in tertiary healthcare facilities which have a large number of cases and financial constraints. The present study aimed to re-evaluate the efficiency of smear microscopy and culture on Lowenstein Jensen (LJ) medium for acid fast bacilli (AFB) isolated from patients with pulmonary tuberculosis. 210 samples were processed for detection of AFB by Ziehl Neelsen (ZN)staining. Concentration method of N-acetly-L-cystein-NaOH was used and the samples were isolated on LJ medium.AFB was seen in 168 (80.0%) primary smear samples. The primary smear missed 5 (11.9%) samples that were detected by secondary smear (Sensitivity 93.45%, Specificity 88.10%, Positive predictive value (PPV) 96.91% and Negative Predictive value (NPV) 77.08%). Growth was observed in 155 (83.30%) samples (Sensitivity 95.39%,Specificity 70.59%, PPV 93.55%and NPV 77.42%). The values were statistically significant. The present study reconfirms the efficiency of conventional ZN staining method and culture on LJ medium in the detection of AFB in sputum samples of patients with pulmonary tuberculosis.