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- Interferon-gamma Release Assay (IGRA) for Mycobacterium tuberculosis
- QFT-Plus
Special Instructions
This test is time-sensitive. Specimens must be incubated at 37°C for 16 to 24 hours prior to transport to LabCorp and specimens must be received in the laboratory within 70 hours after incubation by the client (no more than 94 hours from the time of collection). Specimen collection times will be dependent on logistics from the incubating location to a Labcorp lab.
To submit QuantiFERON-TB Gold Plus specimens that are not client incubated prior to submission, order QuantiFERON®-TB Gold Plus (Test No. 182879).
Expected Turnaround Time
2 - 5 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Related Documents
For more information, please view the literature below.
Specimen Requirements
Specimen
Whole blood
Volume
1 mL x four tubes in QuantiFERON-TB Gold Plus kit
Minimum Volume
1 mL x four tubes in QuantiFERON-TB Gold Plus kit
Container
The QuantiFERON®-TB Gold Plus collection kit contains the instructions for the collection and handling of (one each): (1) gray-top (with white ring), uncoated (nil); (2) green cap with white ring, TB1 tube; (3) yellow cap with white ring, TB2 tube; (4) purple top with white ring, mitogen-coated. A high altitude kit is also available for locations between 3350 and 6150 feet; a cap with a yellow ring differentiates the tubes.
Collection
Blood collection tubes should be at room temperature at the time of collection. Refer to collection instructions included with draw kit. Special specimen collection kit contains four gel-barrier tubes as noted above. All four tubes are required for a single test result. Each tube is designed to draw only 1 mL and fill time may be longer than other blood collection tubes. Because of the limited vacuum in these tubes, use a needle and holder (not a butterfly) to collect QuantiFERON® specimens. If a butterfly is required, first collect other required tubes or use another Vacutainer® tube to purge the butterfly line of air and then proceed with drawing the QuantiFERON tubes. Fill tubes to the black fill line on the tube. If tubes are underfilled or overfilled (see kit insert), immediately collect a replacement tube.
Following proper fill, label the tubes appropriately and shake tubes 10 times firmly enough to ensure the entire surface of the tube is coated with blood cells to solubilize the antigen on the tube walls. After shaking, the volume may fall below the fill line. Do not centrifuge or refrigerate specimens.
Return each of the four properly filled, labeled, and shaken tubes to the box labeled "QFT kit." Seal the top by removing tape from the adhesive.
Storage Instructions
Before incubation at 37°C, maintain specimen at room temperature. Stability: Kit must be incubated within 16 hours of collection.
After incubation, maintain specimen at room temperature (17°C to 27°C). Do not centrifuge, refrigerate, or ship tubes on ice.
Causes for Rejection
Grossly hemolyzed, icteric, or lipemic samples; expired collection tubes; specimen centrifuged, refrigerated, or frozen; specimen more than 94 hours old on receipt by lab; receipt of three tube collection kit; under-filled or over-filled tubes; tubes that do not yield sufficient plasma for testing
Test Details
Use
QuantiFERON-TB Gold Plus is an in vitro diagnostic test using a peptide cocktail of CD4+ and CD8+ T cell antigens to stimulate cells in heparinized whole blood. Detection of interferon-gamma by enzyme-linked immunosorbent assay (ELISA) is used to identify in vitro responses to these peptide antigens that are associated with Mycobacterium tuberculosis infection. QuantiFERON-TB Gold Plus is an indirect test for M. tuberculosis infection (including disease) and is intended for use in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations.
Limitations
A negative QFT-Plus result does not preclude the possibility of M. tuberculosis infection or tuberculosis disease: false negative results can be due to stage of infection, co-morbid conditions that affect immune function, incorrect handling of the blood collection tubes following venipuncture, incorrect performance of the assay, or other individual immunological variables. Heterophile antibodies or non-specific interferon-gamma production from other inflammatory conditions may mask specific responses to CD4+ and CD8+ T cell antigens. A positive QFT-Plus result should not be the sole or definitive basis for determining infection with M. tuberculosis. Incorrect performance of the assay may cause false-positive results. A positive QFT-Plus result should be followed by further medical evaluation for active tuberculosis disease.
Methodology
Whole blood interferon-gamma test measuring responses to CD4+ and CD8+ T cell antigens
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 182893 | QFT-TB Plus (Client Incubated) | 71775-1 | 182885 | QuantiFERON Criteria | 8251-1 | |
| 182893 | QFT-TB Plus (Client Incubated) | 71775-1 | 182886 | QuantiFERON TB1 Ag Value | IU/mL | 64084-7 |
| 182893 | QFT-TB Plus (Client Incubated) | 71775-1 | 182887 | QuantiFERON TB2 Ag Value | IU/mL | 88517-8 |
| 182893 | QFT-TB Plus (Client Incubated) | 71775-1 | 182891 | QuantiFERON Nil Value | IU/mL | 71776-9 |
| 182893 | QFT-TB Plus (Client Incubated) | 71775-1 | 182892 | QuantiFERON Mitogen Value | IU/mL | 71774-4 |
| 182893 | QFT-TB Plus (Client Incubated) | 71775-1 | 182894 | QuantiFERON-TB Gold Plus | 71773-6 |
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The LOINC® codes are copyright © 1994-2021, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf