Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

QTBG
83896
polymorphisms in the pncA gene that have not previously been seen in our laboratory will require
additional testing using a reference broth method to determine their correlation with PZA resistance.
Reference Values:
Pyrazinamide resistance not detected
Clinical References: 1. Somoskovi A, Dormandy J, Parson LM, et al: Sequencing of the pncA
Gene in members of the Mycobacterium tuberculosis complex has important diagnostic applications:
identification of a species-specific pncA mutation in "Mycobacterium canettii" and the reliable and
rapid predictor of pyrazinamide resistance. J Clin Microbiol 2007;45:595-599 2. Dormandy J,
Somoskovi A, Kreiswirth BN, et al: Discrepant results between pyrazinamide susceptibility testing by
the reference BACTEC 460TB method and pncA DNA sequencing in patients infected with multi-drug
resistant W-Beijing Mycobacterium tuberculosis strains. Chest 2007;131:497-501 3. Somoskovi A,
Parson LM, Salfinger M: The molecular basis of resistance to isoniazid, rifampin, and pyrazinamide in
Mycobacterium tuberculosis. Respir Res 2001;2:164-168
Mycobacterium tuberculosis Infection Determination by
QuantiFERON-TB Gold, Blood
Clinical Information: Latent tuberculosis infection (LTBI) is a noncommunicable, asymptomatic
condition that persists for many years in individuals and may progress to tuberculosis disease. The main
purpose of diagnosing LTBI is to consider medical treatment for preventing active tuberculosis disease.
Until recently, the tuberculin skin test (TST) was the only method available for diagnosing LTBI.
Unfortunately, the TST is a subjective test that can be falsely positive for individuals who have been
vaccinated with Bacille Calmett-Guerin (BCG), are infected with other mycobacteria than
Mycobacterium tuberculosis complex, or due to other factors such as a digital palpitation error when
reading the test. The QuantiFERON-TB Gold In-Tube test is a measure of cell-mediated immune
response to antigens simulating the mycobacterial proteins ESAT-6, CFP-10, and TB7.7. Individuals
infected with Mycobacterium tuberculosis complex organisms including Mycobacterium tuberculosis,
Mycobacterium bovis, Mycobacterium africanum, Mycobacterium microti, and Mycobacterium canetti
usually have lymphocytes in their blood that recognize these specific antigens. The recognition process
involves the generation and secretion of the cytokine, gamma interferon (IFN-gamma). The detection
and quantification of IFN-gamma by enzyme-linked immunosorbent assay (ELISA) is used to identify
in vitro responses to TB antigens that are associated with Mycobacterium tuberculosis complex
infection. The ESAT-6, CFP-10, and TB7.7 antigens are absent from the Mycobacterium bovis BCG
strains and from most nontuberculous mycobacteria with the exception of Mycobacterium kanasii,
Mycobacterium szulgai, and Mycobacterium marinum. Numerous studies have demonstrated that
ESAT-6, CFP-10, and TB7.7 stimulate IFN-gamma responses in T cells from individuals infected with
Mycobacterium tuberculosis but usually not from uninfected or BCG-vaccinated persons without
disease or risk for LTBI.
Useful For: Indirect test for Mycobacterium tuberculosis complex infection (latent tuberculosis
infection and active disease)
Interpretation: A positive result indicates that Mycobacterium tuberculosis infection is likely.
However, positive reactivity to proteins present in other mycobacteria such as Mycobacterium kansasii,
Mycobacterium szulgai, and Mycobacterium marinum may cause false-positive results. A positive
QuantiFERON-TB Gold result should be followed by further medical and diagnostic evaluation for
tuberculosis disease (eg, acid-fast bacilli smear and culture, chest x-ray). QuantiFERON-TB Gold is
usually negative in individuals vaccinated with Mycobacterium bovis Bacille Calmett-Guerin.
Reference Values:
Negative
Clinical References: 1. Mori T, Sakatani M, Yamagishi F, et al: Specific detection of tuberculosis
infection: an interferon-gamma-based assay using new antigens. Am J Respir Crit Care Med
2004:170;59-64 2. Kang YA, Lee HW, Yoon HI, et al: Discrepancy between the tuberculin skin test and
the whole blood interferon gamma assay for the diagnosis of latent tuberculosis infection in an
Current as of January 3, 2013 2:22 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1273