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Mycobacterium tuberculosis Complex PCR

Mtb, Acid Fast Bacilli, TB, Tuberculosis, Mtb Complex, Tubercule, MTB/RIF, Rifampin

Test Codes

EPIC: LAB8770

Department

Microbiology

Instructions

Because this test must be accompanied by an AFB culture, if an MTB PCR is ordered without an AFB culture for sputum samples, an AFB culture will be automatically added by the Microbiology Lab.

This test is only available for sputum specimens. For PCR testing on non-sputum samples, order the send out test Mycobacterium tuberculosis Complex, PCR, non-sputum [LAB1230037].

Specimen Collection Criteria

Collect: Sputum (induced or expectorated) in a sterile, leak-proof collection container.

Physician Office/Draw Specimen Preparation

Maintain original specimens refrigerated (2-8°C or 36-46°F) and transport to the Laboratory within 24 hours of collection.

Preparation for Courier Transport

Transport: Sputum and tracheal aspirate specimens, refrigerated (2-8°C or 36-46°F).

Rejection Criteria

• Specimen types other than sputum.
• Unlabeled specimens.
• Specimens contaminated with food or other solid particles.
• Swab specimens.
• This test will not be performed on previously positive patients more frequently than every 12 months.
• This test is limited to 2 orders/30 days for each patient.

Storage

Specimen Stability for Testing:

Original Specimens
Room Temperature (20-26°C or 68-78.8°F): 3 days
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Re-suspended Specimens
Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): Up to 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Royal Oak Microbiology Laboratory

Performed

Sunday – Saturday.
Results available within 24 hours. 

Reference Range

Negative.

Test Methodology

Nucleic Acid Amplification (FDA Approved). 

Interpretation

• A negative result does not rule out MTB infection. The sensitivity of the Xpert MTB/RIF assay on smear-negative specimens is reported to be <70%.
• A positive result indicates the presence of M. tuberculosis complex DNA.
• A “Detected” result for Rifampin resistance indicates presumptive Rifampin resistance through the detection of mutations within the rpoB gene.
• A “Not Detected” result for Rifampin resistance indicates that mutations within the rpoB gene associated with Rifampin resistance were not detected.
• This test does not differentiate among the members of the M. tuberculosis complex (M. tuberculosis, M. bovis, M. bovis BCG, M. africanum, and M. microti).
• Cross-reactions can occur with M. scrofulaceum if present at a concentration greater than 10⁸ CFU/mL.
• A positive or indeterminate result for Rifampin will be sent to a reference laboratory for confirmation. 
• This test is FDA-Approved for smear-positive and smear-negative specimens.

Clinical Utility

To aid in the diagnosis of tuberculosis and in the detection of M. tuberculosis isolates that are resistant to rifampin.

Clinical Disease

Tuberculosis (TB) is caused by Mycobacterium tuberculosis. There are three stages of TB; primary or initial infection, latent or dormant infection, and reactivation TB. Ninety to 95% of primary TB infections are asymptomatic. Patients have a positive tuberculin skin test and a latent or dormant infection. This infection may activate at any age producing clinical TB in whatever organ it inhabits. Approximately 20% of pulmonary TB in adults results from a newly acquired infection, the rest of the cases are due to reactivation of a previously acquired infection. The general symptoms of tuberculosis are: unexplained weight loss, loss of appetite, night sweats, fever, fatigue, and chills. The symptoms of tuberculosis of the lungs include: coughing for 3 weeks or longer, hemoptysis (coughing up blood), and chest pain. Other symptoms depend on the area of the body that is infected.

Epidemiology

The number of cases varies according to county, age, race, sex, and socioeconomic status. In the U.S. in 2019, 8,920 cases of TB were reported. Worldwide, 10 million people are ill with tuberculosis. TB has been almost eliminated in some segments of the population. It is still prevalent in persons greater 70 years old, and TB is twice as prevalent in blacks as in whites in all age groups. TB has also increased greatly in persons with AIDS. There has been an increase in TB caused by drug-resistant organisms. The incidence of TB is increasing and the likelihood of a steeper rise and outbreaks of drug-resistant organisms appears certain.

Incubation Period

Latent or dormant TB infections usually occur within 1-2 years of initial exposure. TB can develop more easily if the immune system is weakened by malnutrition, AIDS, diabetes, cancer, or following treatment with immunosuppressant drugs.

Transmission

In developed countries, M. tuberculosis is spread through airborne particles that are generated when persons with active pulmonary tuberculosis cough or sneeze. The organisms may remain in the room air for several hours, increasing the chance of infecting people who enter the room during this time.

CPT Codes

87581

Contacts

Last Updated

8/26/2025