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Molecular & Growth Detection of NTM & TB

For detailed information about mycobacterial testing, please visit the Advanced Diagnostic Laboratories Test Menu.

National Jewish Health Mycobacteriology Laboratory provides acid-fast bacilli (AFB) microscopy testing, molecular assays (NAAT, MDR TB screen, etc.), primary isolation and growth detection to health care providers throughout the United States.

AFB Testing

Our laboratory provides AFB smear testing from sputum or other clinical specimens within 24 hours using fluorescent microscopy. These acid-fast bacilli assays are performed six days a week and by request on Sunday to ensure rapid identification of highly infectious TB patients.

Molecular Detection: NAAT, MDR-TB

A Nucleic Acid Amplification Test (NAAT) for TB is performed on the first specimen or by request for subsequent specimens. NAAT testing includes screening for amplification inhibition. NAAT results are reported within 24 hours upon receipt or called-in request.

The Centers for Disease Control and Prevention (CDC) recommends that NAAT testing be performed on at least one respiratory specimen from each patient with signs and symptoms of pulmonary TB for whom a diagnosis of TB is being considered but has not yet been established, and for whom the test result would alter case management or TB control activities.

If AFB smear and NAAT are positive, a direct 10-drug agar proportion AST and molecular MDR-TB screen is performed.

In Fall 2012, the Association of State and Territorial Health Officials (ASTHO) recognized the use of a universal laboratory screening test for multidrug-resistant tuberculosis (MDR TB). Reflex testing is beneficial, as it allows the most rapid detection of a MDR TB patient.

Growth Detection

After decontamination, digestion and concentration, four media are inoculated for growth detection (1 broth, 1 Lowenstein-Jensen slant and a 7H11 biplate). Negative cultures are reported after 6 weeks of incubation; LJ slants are incubated for 8 weeks. In the event of growth detection beyond 6 weeks, an amended report is issued.

If colony morphology resembles Mycobacterium tuberculosis (MTB) complex, a TB DNA probe is performed.

If positive, differentiation within the MTB complex and first-line drug antimicrobial susceptibility testing is completed on all initial isolates.

All other mycobacteria are identified using DNA sequencing.