Florida Bureau of Public Health laboratories

QFT-Plus, Interferon-Gamma Release Assay (IGRA)

The QFT Gold Plus test provides qualitative results for the detection of Mycobacterium tuberculosis utilizing IFN-gamma (IFN-g) detection by chemiluminescence immunoassay (CLIA).

Analyte(s)

Mycobacterium tuberculosis

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Test Code

0470

Testing Location

Jacksonville Laboratory

Testing Department

Serology

Pre-approval Required?

Yes, county must be registered with the TB program. Test order is not available for routine testing at this time.

Required Forms

BPHL Test Requisition, DH1847 (not needed if orders are placed by electronic order) AND
QFT-TB TESTING SPECIMEN SUBMISSION FORM

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Minimum Volume

0.8-1.2 mL (fill to the black mark on side of QFT-Plus tubes) or
5 mL of whole blood in a lithium-heparin tube

Turn Around time

4 business days after receipt at the laboratory.

Supply Ordering

Supplies may be requested from your servicing laboratory. Supplies ordered from the BPHL should only be used for specimen sent to the BPHL for testing.

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Collection Media

QFT-Plus tubes or Lithium-heparin tube

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Specimen Sources

Heparinized whole blood

Specimen Labeling

Specimen must be labeled with at least two unique patient identifiers, e.g., name and DOB.

Information on the specimen must match the requisition and/or test order. 

Special SPecimen Preparation

You MUST use a discard tube prior to collecting specimen with a butterfly needle with the 4 colored QFT-Plus tubes.

The QFT-TB TESTING SPECIMEN SUBMISSION FORM needs to be filled out and included in the shipment for each patient specimen collected.

The acceptable range of the room during specimen collection is 17-25° C.
Whole blood may be collected into 4 QFT-Plus tubes or in a single lithium-heparin tube. Follow specimen hold times below: 

A. Direct draw into QFT-Plus tubes – 4 (Nil gray cap, TB1 green cap, TB2 yellow cap, and Mitogen purple cap):
1. Collect 1 mL directly into each of the QFT-Plus tubes. 
2. After collection, the blood needs to be thoroughly mixed with the antigens in the inner wall of the blood collection tubes. 
3. Send to laboratory within 16 hours of collection and delivered at 17-25° C. 

B. Collect 5mL of blood into a single lithium-heparin tube:
1. Store at 17-25° C up to 12hrs or 2-8° C up to 48hrs including the time it takes to ship to the lab.  
2. Send to laboratory within the conditions in B. 1.
 
CALL the Jacksonville laboratory at 904-791-1547 for training on specimen collection, handling, and shipping. 

QFT-Plus Blood Collection Training Video

Storage Conditions


QFT-Plus tubes need to be stored and delivered at 17-25° C and received in the testing laboratory no more than 16 hours after collection.

Single tube Lithium-heparin specimens need to be shipped at 2-8° C and received no more than 48 hours after collection.

Packaging and Shipping

QFT-Plus tubes need to be stored and delivered at 17-25° C and received in the testing laboratory no more than 16 hours after collection.

Single tube Lithium-heparin specimens need to be shipped at 2-8° C and received no more than 48 hours after collection.

Unsatisfactory Specimen

1. Specimens not stored or shipped within temperature and time specifications

2. No patient identification on specimen tube

3. No specimen observed in specimen container

4. Specimen damaged or leaked entirely in transit

5. QFT-Plus tubes with blood not within allowable volume (black marks on tube side)

6. Grossly hemolyzed, icteric or lipemic samples

7. Heat-inactivated

8. Samples containing particulate matter or obvious microbial contamination should not be tested

Interferences and Limitations

1. Combine only results from tubes collected from the patient in the same sampling session. 

2. Inaccurate or indeterminate results may occur if strict adherence to the LIAISON QuantiFERON–TB Gold Plus assay and QuantiFERON-TB Gold Plus blood collection tube instructions is not exercised. 

3. A negative result does not preclude the possibility of M. tuberculosis infection or tuberculosis disease: false negative results can be due to the stage of infection (e.g. specimen obtained prior to the development of cellular immune response), co-morbid conditions that affect immune functions, incorrect handling of the blood collection tubes following venipuncture, incorrect performance of the assay, or other immunological variables. 

4. A positive result should not be the sole or definitive basis for determining infection with M. tuberculosis. Incorrect performance of the assay may cause false-positive responses. 

5. Patients routinely exposed to animals or animal serum products can be prone to interference due to heterophilic antibodies and their results should be evaluated with care. 

6. While ESAT-6 and CFP-10 are absent from all BCG strains and from most known nontuberculous mycobacteria, it is possible that a positive result may be due to infection by M. kansasii, M. szulgai, or M. marinum. If such infections are suspected, alternative testing should be considered. 

7. Performance characteristics of the test in the following groups of individuals has not been extensively evaluated: persons <18 years, pregnant women, those with impaired or altered immune functions or other clinical conditions (HIV, transplant recipient, hematological disorders, malignancies, diabetes, chronic renal failure). 

Reference Range

Negative

Result Indicator: Positive, Negative, or Indeterminate

Reported IU/mL values: Nil, TB1 Ag, TB2 Ag, Mitogen 
Reported calculated IU/mL values: Mitogen minus Nil, TB1 minus Nil, TB2 minus Nil 

Positive: Criteria for Positive: When Nil is ≤ 8.0 and TB1-Nil or TB2-Nil are ≥0.35 and ≥25% of Nil value. 

Negative: Criteria for Negative:  
When Nil ≤ 8.0 and TB1 minus Nil or TB2 minus Nil <0.35 and Mit minus Nil ≥0.50; OR
When Nil ≤ 8.0 and TB1 minus Nil or TB2 minus Nil ≥0.35 and <25% of Nil value and Mit minus Nil ≥0.50. 

Indeterminate: Criteria for Indeterminate: 
When Nil >8.0 ; OR
When Nil ≤8.0 and TB1 minus Nil or TB2 minus Nil <0.35 and Mit minus Nil <0.50; OR
When Nil ≤8.0 and TB1 minus Nil or TB2 minus Nil ≥0.35 and <25% of Nil value and Mit minus Nil <0.50. 

Reference lab

None  

Reflex testing

None

Contact Information

904-791-1547