New Role in TB testing

Quantiferon-TB assay (QFT):

Collect blood-->simulate cells with purified protein derivative (PPD)-->detect IFN-gamma by enzyme immunoassay (EIA), which serve as an indirect indicator of exposure to TB

QFT Gold (QFT-G):
-replaced the PPD antigen with early secreoty antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10)
-phytohemagglutinin (PHA) as a +ve control, a mitogen to ensure cells are responding to antigens
-+ve control must show a production of IFN-gamma >=0.5IU/ml
-positive immune response to TB if IFN-gamma >=0.35IU/mi after substracting the value of the Nil control
-IFN-gamma <0.35IU/ml and IFN-gamma of +ve control >=0.5IU/ml ==> unlikely to have TB infection



The manufacturer’s package insert states that a positive QFT result does not “necessarily indicate the presence or absence of active tuberculosis disease.” Other diagnostic procedures, such as mycobacterial culture and radiologic examination, should be used when there is clinical suspicion of TB disease.