Histocompatibility & Immunomonitoring Laboratories
Supervisor’s Name: Frank Salman, NRM (AAM), M(ASCP)
Telephone No.: (305) 243-6615
Order Abbreviation: QTFTB
Method: Mycobacterium tuberculosis antigen-stimulated interferon-gamma production with detection by enzyme linked immunosorbent assay (ELISA). Test includes PHA(positive) and nil (negative) controls
** Source: Whole blood
Collection Notes: 1mL x three tubes The QuantiFERON® collection kit contains instructions for the draw of three special QuantiFERON® collection tubes (one each): (1) gray-top (with white ring), uncoated (nil); (2) red-top (with white ring), TB antigen-coated; (3) purple-top (with white ring), mitogen coated. This test is time-sensitive and specimens must be received in the laboratory within 14 hours of collection. Maintain specimen at room temperature (17-27 degree C) Do not centrifuge, refrigerate, or ship on ice.
Limitations: Spontaneous interferon-gamma production (independent of TB stimulation) or lack of a response to mitogen (due to anergy or immune suppression) may render the results indeterminate. A negative result should not be used alone to exclude M. tuberculosis infection in persons with symptoms or signs suggestive of TB disease. Those who have a negative result, but who are likely to have latent TB infection (LTBI) and who are at greater risk for severe illness or poor outcome if TB disease occurs, might need treatment or closer monitoring for disease. The QuantiFERON® TB test has been shown to be accurate in HIV-positive individuals with moderately advanced disease, but in the severely immunocompromised the test may be impaired by T-cell anergy. Active TB disease may result in a negative test as reduction of in vitro IFN-gamma release has been described and may be due to suppressive cytokines associated with TB disease. Patients with mycobacterial infections, other than tuberculosis, might also be responsive to ESAT-6, CFP-10, and TB7.7 as the genes encoding these proteins are present in M kansasii, M szulgai, and M marinum.
Additional Information: Tuberculosis (TB) is a highly contagious respiratory disease caused by bacteria of the Mycobacterium tuberculosis complex (M tuberculosis, M bovis, and M africanum). In the US, tuberculosis is relatively uncommon, due to public health efforts; however, latent TB infection, which is a noncommunicable asymptomatic condition, is more common. Latent tuberculosis infection (LTBI) results when a person becomes exposed to M tuberculosis and their body controls, but does not eradicate the infection. It is estimated that 11 million people in the US have LTBI6 and anticipated that approximately 10% of these will progress to active TB during the course of their lifetime. Immunosuppression, as occurs in HIV infection or with certain therapies (eg, TNFα inhibitors), can result in reactivation of the LTBI and development of infectious tuberculous disease. Diagnosis of LTBI is an important step in preventing reactivation of tuberculosis, particularly in at-risk populations. Treatment of LTBI can markedly reduce the risk of progression to active disease. The QuantiFERON®-TB Gold assay has been approved by the FDA as an in vitro test to aid in the diagnosis of M tuberculosis infection. The test uses three recombinant peptides from M tuberculosis (ESAT-6, CFP-10, and TB7.7) to stimulate T-cell interferon-gamma production in individuals with M tuberculosis infection. These peptide antigens do not usually stimulate lymphocytes from uninfected, BCG-vaccinated persons without disease or risk for LTBI. In the past, the tuberculin skin test (TST or Mantoux reaction) was the only method for assessing TB infection. Although widely used, the TST had a number of limitations that have been addressed in the QuantiFERON®-TB Gold assay. For this laboratory assay, the stimulation of lymphocytes with M tuberculosis antigens occurs in the phlebotomy tube, rather than in the patient's arm. As a result, there is no booster effect from repeated testing (as is the case with the TST). Results of the QuantiFERON®-TB Gold test are available following a single patient visit without the need for a second visit to evaluate the skin test. The in vitro assay is not associated with adverse hypersensitivity reactions. The recombinant antigens chosen as stimulants in the new assay are not present in the BCG vaccine; therefore, the assay is more specific and prior BCG vaccination will not cause false positives in this test, as it does in the TST. In addition, the interpretation of the lab test is more objective than the TST result. Numerous clinical studies have demonstrated that the interferon-gamma release assays are a sensitive and specific method for the assessment of tuberculosis infection (both latent and active disease). The CDC has recommended this test for use in all settings where skin testing is applicable, including contact investigations, evaluation of recent immigrants, and sequential-testing surveillance programs for infection control (eg, those for health care workers). Additional utility may be found in the setting of iatrogenic immunosuppression (eg, anti-TNF therapy for rheumatologic conditions) where the identification of LTBI prior to therapy may help prevent subsequent TB disease. A positive result indicates that TB infection is likely and should prompt the same public health and medical interventions as a positive TST result. No reason exists to follow a positive QuantiFERON®-TB Gold result with a TST; however, because of the higher specificity, the QuantiFERON®-TB Gold may have value in excluding a diagnosis of TB infection among individuals with positive TST results caused by nontuberculous mycobacteria, thereby reducing overdiagnosis of TB and guiding clinical management. Persons who have a positive QuantiFERON®-TB, regardless of symptoms or signs, should be evaluated for TB disease before LTBI is diagnosed. The majority of healthy adults who have negative QuantiFERON®-TB Gold results are unlikely to have M tuberculosis infection and do not require further evaluation; however, for persons with recent contact with persons who have infectious TB, negative QuantiFERON®-TB Gold results should be confirmed with a repeat test performed weeks after the end of exposure, as is recommended for a negative TST result.
Turnaround Time: 7 Days
CPT Code: 86480
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