Tuberculosis

Tuberculosis (TB) is caused by exposure to Mycobacterium tuberculosis (M. tuberculosis), which is spread through the air from one person to another. At least two billion people are thought to be infected with TB and it is one of the top ten causes of death worldwide. To fight TB effectively and prevent future disease, accurate detection and treatment of Latent Tuberculosis Infection (LTBI) and Active TB disease are vital.

M. tuberculosis is put into the air when an infected person coughs, speaks, sneezes, spits or sings. People within close proximity may inhale these bacteria and become infected. M. tuberculosis usually grows in the lungs and can attack any part of the body, such as the brain, kidneys and spine. While people with LTBI have no symptoms, people with Active TB disease show symptoms depending on the infected area of the body. TB disease in the lungs may cause symptoms such as a cough lasting three weeks or longer and coughing up blood or sputum and chest pain. Other symptoms can include: chills, fatigue, fever, weight loss and/or loss of appetite and night sweats.

Biochemistry

T-lymphocytes of individuals infected with M. tuberculosis secrete interferon-gamma (IFN-γ) when they are exposed to specific antigens displayed by M. tuberculosis. The tuberculosis screen measures the IFN-γ levels in a whole blood specimen using a very sensitive interferon-gamma release assay (IGRA). Specifically, the diagnostic test detects cell-mediated immune response to two proteins that are made by M. tuberculosis but that are absent from most other related mycobacteria species with the exception of M. kansasii, M. szulgai and M. marinum. In addition, the proteins are absent from patients that have received the Bacillus Calmette-Guerin (BCG) vaccine.

QuantiFERON-TB Gold Plus Test

BioReference® offers QuantiFERON-TB Gold Plus® (QFT), a highly specific, controlled diagnostic blood test for detecting exposure to M. tuberculosis using whole blood specimen. QFT provides the value of a robust technology, and offers healthcare providers a more reliable and convenient tool for accurately identifying M. tuberculosis complex, which includes M. tuberculosis, M. africanum and M. bovis.

QTF is able to measure the levels of IFN-γ and correlate those levels to the presence or absence of TB disease. When compared with other IGRA products, which require subjective counting of spots, QFT provides quantitative detection with a user-friendly workflow.

QFT has unique blood tubes, enabling immediate exposure of blood lymphocytes to highly specific TB antigens and test controls coated on the inner surface of the tubes. Once the sample reaches the lab, the Nil tube (negative control) adjusts for background IFN-γ. The Mitogen tube serves as a positive control and can be useful for indicating correct sample handling and incubation, as well as a patient’s immune status. The TB1 and TB2 Antigen tubes provide a more comprehensive view of the immune response to a TB infection through use of CD4/CD8 technology.

Test Benefits

QFT can aid in the diagnosis of both active TB disease and LTBI. It is applicable to all patient groups that would be candidates for the traditional tuberculin skin test, but has several significant benefits, including:

• Accuracy: QFT is a blood test that assesses the production of gamma interferon by a type of white blood cell, and is a sensitive test for exposure to TB. A positive result means that the patient has been exposed to the M. tuberculosis bacterium, which may be either latent (asymptomatic) or active. Most results of the test (>95%) result in either a positive or negative result, and are not affected by compromised immunity, such as that seen in HIV patients.
• Convenience: QFT can generate the desired disease information after a single patient visit, whereas a TB skin test must be evaluated by a clinician in a subsequent visit days later.
• Reliability: The TB skin test requires an intradermal injection, which is subject to health provider error in administration. It also requires a second visit to the health care provider after 2-3 days to interpret the test. False positives with the skin test may occur in the setting of vaccination/administration, and false negatives may occur in immunocompromised patients.

 Patient Considerations

To reduce disparities related to TB, screening, prevention and control efforts should be targeted to the populations at greatest risk, including:

• Healthcare workers
• Military personnel
• The elderly
• Students
• Immigrants
• International travelers
• Residents of long-term care facilities
• People with weakened immune systems
• Persons living in correctional facilities or other congregate settings
• Close contacts of persons known or suspected to have Active TB

The US Centers For Disease Control And Prevention (CDC) guidelines recommend the use of an IGRA in all situations in which the TB skin test was traditionally used, with IGRA being the preferred test for persons who have been BCG-vaccinated or are unlikely to return for TB skin test readings.

Specimen Collection Instructions