Sorted By Test Name - Mayo Medical Laboratories

MPA
81563
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
intermediate tuberculosis burden country. JAMA 2005:293;2756-2761 3. Ferrara G, Losi M, Meacci M, et
al: Routine hospital use of a commercial whole blood interferon-gamma assay for tuberculosis infection.
Am J Respir Crit Care Med 2005 as doi:10.1164/rccm.200502-1960C
Mycophenolic Acid, Serum
Clinical Information: Mycophenolate mofetil (CellCept) is a new immunosuppressive agent useful
in organ transplantation. It is approved for use in renal, hepatic, and cardiac transplants. When
mycophenolate mofetil enters the blood, it is immediately metabolized to the active drug, mycophenolic
acid (MPA), which inhibits inosine monophosphate dehydrogenase and interferes with the de novo
pathway of guanosine nucleotide synthesis selectively in lymphocytes. MPA inhibits proliferative
responses of T- and B-lymphocytes to both mitogenic and allospecific stimulation. MPA acts in the same
fashion as azathioprine, and MPA is suggested as replacement therapy for azathioprine. The drug is
deactivated by the hepatic enzyme, uridine diphosphate glucuronosyltransferase (UGT) to form
mycophenolic acid glucuronide (MPA-G). The principle clinical problem encountered in MPA therapy is
excessive immunosuppression, which predisposes the patient to systemic infection. Measurement of the
blood level of MPA and MPA-G can be useful to guide therapy. Monitoring is recommended immediately
after transplant up to 3 weeks after therapy is initiated to evaluate dosing adequacy. Additional monitoring
is indicated if the MPA level is not in the therapeutic range or if a major change in health status occurs.
Useful For: Monitoring therapy with CellCept to ensure adequate blood levels and avoid
Current as of January 4, 2013 7:15 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1267