Detection of Mycobacterium tuberculosis in clinical samples by smear and culture

Objective: To compare the smear stained by Ziehl-Neilsen (ZN) and Lowenstein-Jensen (LJ) medium for the detection of Mycobacterium tuberculosis in clinical samples from different categories. Materials / Methods: This laboratory based retrospective study was carried out at Sir Ganga Ram Hospital / Fatima Jinnah Medical College, Lahore over a 5 year period between January 2001and June 2006. A total of 798 clinical samples were collected from patients with a provisional diagnosis of tuberculosis. A ZN stain of smear and culture on LJ medium were performed for the detection of Mycobacterium. The specimen categories were sputum, pus, lymph node aspirate, urine and endometrial curetting. Results: Out of 798 specimens received over the study period, only 46.3% (n=369) were respiratory whereas 53.7% (n=429) were non respiratory tract category samples. Among these, 3.578% were positive in ZN stain while 11.65% were positive on culture. Out of a total of 369 respiratory tract category samples, 38(10.3%) sputum samples were positive for AFB on both ZN and culture. Among the non respiratory tract category, 47(28.2 %) pus, 26(31%) lymph node aspirates, 05(15.6%) urine, 05(3.42%) endometrial curetting were positive. Conclusion: Fifteen percent of clinical samples belonging to 05 different categories of specimens with a provisional diagnosis of tuberculosis, tested positive for Mycobacterium by both Zn stain smear and culture on LJ medium. Among these, 3.57% were positive for AFB on ZN smear and 11.65 % were positive on culture on LJ medium. These conventional techniques have proved to be reliable testing tools for detection of Mycobacterium tuberculosis in our setting.