Many mycobacterial species, including M. tuberculosis, grow extremely slowly in the laboratory and require 3–8 weeks of incubation on solid medium or at least 2 weeks in a radiometric liquid culture system (BACTEC). This slow growth often leads to delay in TB diagnosis. Nucleic acid amplification (NAA) methods allow for detection of mycobacterial DNA or RNA directly from the specimens before the culture results are available. The Food and Drug Administration (FDA) has approved two NAA tests for direct detection of M. tuberculosis from clinical specimens. These are the Enhanced Mycobacterium tuberculosis Direct Test (E-MTD; Gen-Probe, San.
