Résumé
OBJECTIVES: The conventional methods such as smear or culture of Mycobacteria have been proved either low sensitivity and specificity or time-consuming. Polymerase chain reaction (PCR) is a rapid and sensitive alternative method to diagnose mycobacterial infection. We investigated the positive rate of sputum PCR for Mycobacterium tuberculosis by consecutive tests for its application in clinical practice. METHODS: Sputum AFB smear, culture and serial AFB PCR test were performed in all patients who were suspected of pulmonary tuberculosis. Among them, 128 patients with positive sputum PCR test were enrolled from January 1996 through March 1997. The diagnostic criteria of pulmonary tuberculosis were sputum AFB smear positive, culture positive or pathologically proven granuloma. TB-CR TM kit (Bioneer, seoul, Korea), which amplifies insertion sequence (IS6110) of Mycobacterium tuberculosis complex, was used for sputum AFB PCR. RESULTS: Of 128 patients, active pulmonary tuberculosis were 107 (male:74, female:33, mean age:48.9 year). Cumulative positive rate of sputum AFB PCR test was 89% at 1st test, 95% at 2nd test, 98% at 3rd test and 100% at 4th test. The sensitivity of sputum PCR, smear and culture was 98.0% (105/107), 85.0% (91/107) and 82.8% (77/107), respectively. The positive predictive value of sputum PCR was 83.6% (107/128). There were 21 patients who showed positive PCR test did not meet the diagnostic criteria of active tuberculosis. They had old tuberculosis with destroyed lung, history of anti- tuberculous medication (9/21), extrapulmonary tuberculosis (6/21) and other diseases (6/21). CONCLUSION: Sputum PCR test is a sensitive diagnostic tool in early diagnosis of pulmonary tuberculosis when it has been performed serially, we recommend at least 2 consecutive PCR test to achieve the sensitivity of 95%.