Mycobacterium tuberculosis Infection Determination by QuantiFERON-TB Gold, Blood
Method Description Describes how the test is performed and provides a method-specific reference
The QuantiFERON-TB Gold In-Tube test utilizes peptide cocktail simulating ESAT-6, CFP-10, and TB7.7 proteins, which are used to stimulate T cells in whole heparinized blood during incubation. The test is performed in 2 stages. First, 1 mL of whole blood is collected into each of 3 collection tubes: Nil control tube, TB antigen tube, mitogen tube. Tubes are incubated at 37 degrees C within 16 hours of collection. Following a 16 to 24 hour incubation period, the tubes are centrifuged and the plasma is used to test for the amount of interferon-gamma (IFN-gamma) present, measured by enzyme-linked immunosorbent assay.
A test is considered positive for an IFN-gamma response to the TB antigen tube that is significantly above the negative control (Nil tube) value (IU/mL). The mitogen-stimulated plasma sample (mitogen tube) serves as an IFN-gamma positive control for each sample tested. A low response to mitogen (<0.5 IU/mL) is an indeterminate result when a blood sample also has a negative response to the TB antigens. This pattern may occur with insufficient lymphocytes, reduced lymphocyte activity due to prolonged specimen transport or improper specimen handling, or inability of the patient's lymphocytes to generate IFN-gamma. The negative (Nil) sample adjusts for background, heterophile antibody effects, or nonspecific IFN-gamma in blood samples. The IFN-gamma level of the negative control is subtracted from the IFN-gamma level for the TB antigen tube and mitogen tube. (Package insert: QuanitFERON-TB Gold (In-Tube Method), Cellestis Limited, Carnegie, Victoria, Australia, document number 05990301B, January 2007)
Note: Tuberculosis antigen IU/mL value is reported (TB Ag IU/mL Value). This information may be required for certain CDC reporting forms (eg, Form I-693).
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Friday
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
External: Until testing is complete
Performing Laboratory Location The location of the laboratory that performs the test