Test Catalog

Test ID: MTBXP    
Mycobacterium tuberculosis complex, Molecular Detection, PCR, Sputum

Useful For Suggests clinical disorders or settings where the test may be helpful

Rapid detection of Mycobacterium tuberculosis DNA from respiratory specimens for the diagnosis of pulmonary tuberculosis


Presumptive detection of rifampin resistance based on the presence of resistance-associated mutations

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Mycobacterium tuberculosis is a highly transmissible bacterial pathogen and is the causative agent of tuberculosis, a disease causing significant worldwide morbidity and mortality. Each year, M tuberculosis accounts for nearly 1.3 million deaths and is responsible for 10 million newly diagnosed cases of tuberculosis worldwide. M tuberculosis is spread from person to person via respiratory transmission, and has the potential to become resistant to many of the antibiotics currently used if not treated appropriately. Therefore, rapid and accurate detection of M tuberculosis in patient specimens is of clinical and public health importance.


Conventional culture methods can generally detect M tuberculosis in 2 to 3 weeks, although up to 6 weeks of incubation may be required in some instances. This qualitative molecular assay utilizes PCR-based nucleic acid amplification for the direct detection of M tuberculosis DNA within respiratory specimens without relying on culture growth, leading to more rapid diagnoses and appropriate patient care. This assay also detects the presence of mutations in the rpoB gene that have been documented to confer more than 95% of cases of rifampin resistance.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Interpretation Provides information to assist in interpretation of the test results

A positive result indicates the presence of Mycobacterium tuberculosis complex DNA.


A negative result indicates the absence of detectable M tuberculosis complex DNA.


Presumptive rifampin (RIF) resistance mediated through mutations within the resistance determining region of the rpoB gene will be reported when detected.


One to 2 negative PCR results in conjunction with 1 to 2 negative acid-fast smears may provide evidence supporting the removal of a patient from airborne isolation. Consult your local Infection Prevention and Control for guidance.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test should always be performed in conjunction with mycobacterial culture, which is required for epidemiological strain typing and definitive drug susceptibility testing.


Per current CDC recommendations, rifampin resistance results should be considered as preliminary pending confirmation with gene sequencing or growth-based phenotypic drug susceptibility testing.


This PCR-based molecular assay detects Mycobacterium tuberculosis nucleic acid and, therefore, does not distinguish between viable, disease-related organisms and nucleic acid persisting from prior infection. Test results should be correlated with patient symptoms and clinical presentation before a definitive diagnosis is made.


A negative result does not rule-out infection with M tuberculosis or active disease because the organism may be present at levels below the limit of detection for this assay.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. World Health Organization. Global Tuberculosis Report, 20th edition. Geneva, Switzerland. 2015 Available at www.who.int/tb/publications/global_report/gtbr15_main_text.pdf

2. Centers for Disease Control and Prevention. Availability of an assay for detecting Mycobacterium tuberculosis, including rifampin-resistant strains, and considerations for its use - United States, 2013. MMWR Morb Mortali wkly rep 2013;62:821-827

3. Boehme CC, Nabeta P, Hillemann D, et al: Rapid Molecular Detection of Tuberculosis and Rifampin Resistance. N Engl J Med 2010;9:1005-1015

4. Food and Drug Administration. New data shows test can help physicians remove patients with suspected TB from isolation earlier. Press Release. 2015 Feb 12. Available at www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm434226.htm