Test Catalog

Test Id : MTBT

Mycobacterium tuberculosis Complex, Molecular Detection, PCR, Paraffin, Tissue

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

Preferred method for rapid detection of Mycobacterium tuberculosis complex DNA in formalin-fixed, paraffin-embedded tissue specimens


Detecting M tuberculosis complex


This test is not intended for the detection of latent tuberculosis and must not be used as a substitute for tests intended for detection of latent tuberculosis such as the tuberculin skin test or an interferon gamma release assay.

Method Name
A short description of the method used to perform the test

Real-Time Polymerase Chain Reaction (PCR)

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.


Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

MTB complex PCR, FFPE

Lists additional common names for a test, as an aid in searching

Acid-Fast Bacilli (AFB)

AFB (Acid-Fast Bacilli)

Bacillus, Acid-Fast

MTB (Mycobacterium tuberculosis)

Mycobacterium tuberculosis (MTB)

TB (Tuberculosis)

Tubercle Bacilli: Mycobacterium tuberculosis

Tuberculosis (TB)

Specimen Type
Describes the specimen type validated for testing

Tissue, Paraffin

Additional Testing Requirements

When non-fixed specimen is available, a mycobacterial culture on that specimen must always be performed in addition to this test. If your facility is unable to perform mycobacterial culture, order CTB / Mycobacteria and Nocardia Culture, Varies concurrently with this test.

Necessary Information

Specimen source is required.


Question ID Description Answers
SRCTB MTB Complex PCR, FFPE, Source

Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing

The high sensitivity of amplification by polymerase chain reaction requires the specimen to be processed in an environment in which contamination of the specimen by Mycobacterium tuberculosis DNA is unlikely.


Preferred Paraffin-embedded tissue block:

Supplies: Tissue Block Container (T553)

Specimen Type: Formalin-fixed, paraffin-embedded tissue block (FFPE)

Sources: Body tissue

Container/Tube: Tissue block

Collection Instructions: Submit a FFPE tissue block to be cut and returned.


Acceptable Paraffin-embedded tissue block:

Specimen Type: Formalin-fixed, paraffin-embedded tissue block (FFPE)

Sources: Body tissue

Container/Tube: Sterile container for each individual cut section (scroll).

Collection Instructions: Perform microtomy and prepare five separate 10-micron sections. Each section (scroll) must be placed in a separate sterile container for submission.

Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

See Specimen Required.

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Any non-formalin-fixed, paraffin-embedded tissue block(FFPE)
FFPE slides
FFPE body fluids

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Specimen Type Temperature Time Special Container
Tissue, Paraffin Ambient (preferred)

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

Preferred method for rapid detection of Mycobacterium tuberculosis complex DNA in formalin-fixed, paraffin-embedded tissue specimens


Detecting M tuberculosis complex


This test is not intended for the detection of latent tuberculosis and must not be used as a substitute for tests intended for detection of latent tuberculosis such as the tuberculin skin test or an interferon gamma release assay.

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

Each year, Mycobacterium tuberculosis accounts for approximately 1.4 million deaths and is responsible for 9 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 or all antibiotics currently used if antimycobacterial treatment is not promptly initiated. 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 8 weeks of incubation may be required in some instances. Developed at Mayo Clinic, this rapid polymerase chain reaction (PCR) assay detects M tuberculosis complex DNA directly from respiratory specimens and other specimens without waiting for growth in culture. Therefore, the results are available the same day the specimen is received in the laboratory. A mycobacterial culture should always be performed in addition to the PCR assay. This assay is rapid, but the culture has increased sensitivity over it. The PCR assay targets a unique sequence within the katG gene, which is present in members of the M tuberculosis complex. In addition, the assay can detect genotypic resistance to isoniazid mediated by variants in the katG target, when present.

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.

Not applicable

Provides information to assist in interpretation of the test results

A positive result indicates the presence of Mycobacterium tuberculosis complex DNA. Members of the M tuberculosis complex detected by this assay include M tuberculosis, Mycobacterium bovis, Mycobacterium bovis bacillus Calmette-Guerin (BCG), Mycobacterium africanum, Mycobacterium canettii, and Mycobacterium microti. The other species within the M tuberculosis complex (eg, Mycobacterium caprae, Mycobacterium pinnipedii, and Mycobacterium mungi) should, in theory, be detected using the primer and probe sequences in this assay, but they have not been tested at this time. This assay method does not distinguish between the species of the M tuberculosis complex.


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


Isoniazid (INH) resistance mediated through a katG variant will be reported when observed but lack of a katG variant does not imply that the isolate is susceptible to INH. There are other genetic loci in addition to katG that can contribute to resistance for this drug.


An inhibition result indicates that inhibitors are present in the specimen that could prevent the detection of M tuberculosis DNA. A new specimen can be resubmitted under a new order, if desired.

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

This rapid polymerase chain reaction (PCR) assay detects Mycobacterium tuberculosis complex 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 the presence of M tuberculosis complex or active disease because the organism may be present at levels below the limit of detection for this assay.


This test has not been studied for use with specimens from patients being treated with antituberculous agents and, therefore, should not be used to determine bacteriologic cure or to monitor response to therapy. It is not known how long the PCR assay can remain positive following treatment for M tuberculosis.


The sensitivity of this test from formalin-fixed, paraffin-embedded tissue is approximately 63%; therefore, testing of additional specimens should be considered if the result from the first specimen is negative.


A mycobacterial culture on a non-formalin-fixed specimen must always be performed in addition to the PCR test when non-fixed specimen is available. If your facility is unable to perform a mycobacterial culture, CTB / Mycobacteria and Nocardia Culture, Varies  should be ordered.


The sensitivity of the PCR assay from acid-fast smear positive specimens is approximately 96% compared to mycobacterial culture, but sensitivity of the PCR from a smear negative specimen is lower, and a negative result does not rule out M tuberculosis complex.

Supportive Data

The analytical specificity of the assay was determined using Basic Local Alignment Search Tool (BLAST) analysis of the National Center for Biotechnology Information GenBank database, and no sequences were detected that would interfere with the LightCycler polymerase chain reaction (PCR) assay. Further, the assay was tested using a panel of 104 respiratory pathogens (bacteria and viruses) that were extracted and subjected to the LightCycler PCR assay. As predicted, only Mycobacterium tuberculosis complex was detected from this panel. In addition, nearly 100 species of nontuberculous mycobacteria were evaluated using this PCR assay and there was no cross-reactivity detected. The analytical sensitivity of the assay was determined to be 10 target copies/microliter using a dilution series of M tuberculosis spiked into respiratory specimens in triplicate.


The inhibition rate from formalin-fixed, paraffin-embedded tissue was 37% (19 of 30 spiked specimens were positive).


Two melt peaks can be produced during this assay. A melt peak at a Tm 64.0 degrees C + or - 2.5 degrees C can correspond to either isoniazid-susceptible or isoniazid-resistant M tuberculosis and, therefore, no indication of isoniazid susceptibility is provided for these isolates. However, an isolate with a melt peak occurring at a Tm of 58.0 degrees C + or - 2.5 degrees C correlated with isoniazid resistance determined using a broth reference method in 100% (26/26) of isolates tested. Isolates with a peak at a Tm of 58.0 degrees C + or - 2.5 degrees C are reported as "Positive, probable isoniazid resistance detected." The PCR result is available 7 to 14 days prior to the broth method and, therefore, may be helpful in selecting appropriate antibiotic therapy for these patients. Confirmation of isoniazid resistance must be ordered if the isolate grows in culture.

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

1. Iseman MD: A Clinician's Guide to Tuberculosis. 2nd ed. Lippincott Williams and Wilkins; 2013

2. American Thoracic Society; Centers for Disease Control and Prevention; Infectious Diseases Society of America. Treatment of tuberculosis. MMWR Recomm Rep. 2003 Jun 20;52(RR-11):1-77. Erratum in: MMWR Recomm Rep. 2005 Jan 7;53(51):1203

Method Description
Describes how the test is performed and provides a method-specific reference

Following specimen processing, genomic DNA is extracted, and the purified genomic DNA is placed on the LightCycler instrument, which amplifies and monitors, by fluorescence, the development of target nucleotide sequences after each polymerase chain reaction (PCR) cycle. A specific target sequence from a portion of the katG gene from Mycobacterium tuberculosis complex is amplified and the resulting segment is detected by melt-curve analysis using sequence-specific fluorescence resonance energy transfer hybridization probes. The LightCycler PCR assay is a closed PCR system that greatly reduces the potential for false-positive results due to specimen cross-contamination as compared with traditional open-system PCR or other amplification methods like transcription-mediated amplification.(Unpublished Mayo method)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Friday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

5 to 7 days

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

7 days; after which time the block will be returned to the client

Performing Laboratory Location
Indicates the location of the laboratory that performs the test


Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.

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  • Prospective clients should contact their Regional Manager. For assistance, contact Customer Service.

Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.


LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
MTBT MTB complex PCR, FFPE 38379-4
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
SRCTB MTB Complex PCR, FFPE, Source 31208-2
TBRR MTB Complex PCR, FFPE, Result 38379-4

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports