ABSTRACT

               The notable increase in the new cases of tuberculosis and the evident limitation of the currently used conventional micro-biological techniques have prompted the development of  rapid and specific diagnostic tests for direct detection of Mycobacterium tuberculosis in clinical specimens. Most of these tests have involved the amplification of small amounts of mycobacterial nucleic acid and of which, the best known is the polymerase chain reaction (PCR). This study was conducted prospectively to compare the results of PCR with those of conventional methods (sputum direct smear and culture) in the diagnosis of pulmonary T.B. The study included 50 patients with suspected pulmonary T.B. (study group, group A) and another 10 patients with pulmonary diseases other than T.B. as control group (group B). All patients were subjected for thorough history, complete clinical examination, complete biochemical examination, tuberculin skin test, chest X–ray (P–A and lateral views), sputum direct smear for acid-fast bacilli (AFB), sputum culture for AFB and PCR examination of the sputum samples. Pulmonary tuberculosis was finally confirmed in 45 0ut of 50 patients (90%) in the study group. Forty-four cases (97.8%) were diagnosed by positive cultures and one case (2.2%) by complete clinical and radiographic improvement with antituberculous therapy. Forty-five patients (90%) in the study group had abnormal chest X-ray findings ranging from minimal to moderately advanced and far advanced lesions (the predominant lesion was the minimal, 38%). Tuberculin test had sensitivity, specificity, positive and negative predictive values of 80%, 60%, 85.7% and 50% respectively. The sensitivity, specificity, positive and negative predictive values of direct smear were 75.5%, 100%, 100% and 57.7% respectively. The sensitivity, specificity, positive and negative predictive values of culture were 97.8%, 100%, 100% and 93.7% respectively. The PCR had sensitivity, specificity, positive and negative predictive values of 86.7%, 93.3%, 97.5% and 70% respectively. The differences between results of tuberculin test and direct smear in relation to culture results in patients with proven pulmonary T.B. were significant statistically while those between results of direct smear and culture in relation to PCR results were statistically insignificant. From this study it can be concluded that PCR is a reliable, rapid and specific diagnostic test and in diagnosing pulmonary T.B. it has the advantages of both conventional methods