Rapid laboratory diagnosis of tuberculosis in clinical practice

: The laboratory diagnosis of tuberculosis relies on direct microscopy of smears for acid-fast bacilli and culturing. Microscopy is a rapid, but neither sensitive nor specific diagnostic method. Cultivation on solid media is a time-consuming procedure, and isolation and identification of Mycobacterium tuberculosis takes 3-8 weeks. Introduction of new selective liquid media with a sensitive growth-detection system, dramatically decreased time necessary for isolation and susceptibility testing, so that positive results can be obtained in two weeks. However, wide use of these systems is limited by high cost of instruments and media. Nucleic acid amplification techniques have in recent years been introduced in clinical laboratories for diagnosis of tuberculosis. Amplification techniques are highly sensitive and specific, and positive results are available in a few hours. Nevertheless, molecular methods cannot replace culturing, when drug susceptibility testing is required.