Comparative Performance Analysis of Different Methods of Diagnosis in Patients with Suspected Pulmonary Tuberculosis

Dr. Aparna Aparajita; Dr. Manoj Kumar; Dr. Ashok Kumar Sharma

Volume : IX, Issue : VIII, August - 2020

Comparative Performance Analysis of Different Methods of Diagnosis in Patients with Suspected Pulmonary Tuberculosis

Dr. Aparna Aparajita, Dr. Manoj Kumar, Dr. Ashok Kumar Sharma

Abstract :

Background: Tuberculosis occurs in every part of world and India accounts for two thirds of new TB cases. A number of tests are available to diagnose TB, ranging from conventional microscopy to nucleic acid tests which are new tools for rapid and early diagnosis. The conventional microscopy has low sensitivity and culture is considered as gold standard but takes ample time for positivity. The newer outlook with nucleic acid amplification tests provide rapid and early detection of tuberculosis with rifampicin resistance especially in patients with high clinical suspicion of infection with Mycobacterium tuberculosis as well as decrease the transmission of disease. The study was carried out to compare such rapid tests with liquid culture and microscopy using ZN stain and AO stain. Aim: To evaluate the sensitivity, specificity, positive predictive value, negative predictive value of nucleic acid amplification testing (CBNAAT) using sputum samples in patients suspected of pulmonary tuberculosis and compare with AFB smear microscopy using ZN stain, AO stain and acid fast bacilli culture (AFB liquid culture). Materials and Methods: The study was a cross sectional study conducted from April 2018 to October 2018 in Department of Microbiology, RIMS, Ranchi. A total of 157 sputum samples were tested. The sensitivity, specificity, positive predictive value, negative predictive value of CBNAAT, ZN stain, AO stain were calculated using Liquid culture of Mycobacterium tuberculosis by MGIT 960 as reference standard. Results: A total of 157 samples were evaluated . Out of these 28 were positive by all the four methods. The sensitivity, specificity, PPV & NPV of CBNAAT were 89.6%, 82.8%, 75.3% and 93.1% . The sensitivity, specificity, PPV & NPV of AFB smear microscopy using ZN stain were 48.3%, 100%, 100% and 76.7% and that of fluorescent microscopy with AO stain were 75.8%, 91.9%, 84.6% & 86.7% respectively. Conclusion: CBNAAT has higher sensitivity than AFB smear microscopy in sputum samples. Fluorescent microscopy has higher sensitivity than conventional microscopy and can help detect the bacteria in samples with less bacterial load in lesser time. Culture is the gold standard and so results that are culture negative but CBNAAT positive should be correlated with history and clinical presentation.