QUANTIFERON-TB ASSAY

Collect  5 mL of whole blood into a 6 mL blood collection tube containing Lithium-Heparin as the anticoagulant.   

Alternately, collect a minimum of 3mL of whole blood into each of the two 4 mL Lithium-Heparin blood collection tubes.

Special pre-approved events will have separate collection criteria- see * note section below.

Lithium Heparin tube (dark green cap)  

5 mL in single 6 mL blood collection tube containing Lithium-Heparin as the anticoagulant.

Alternately, 3 mL of whole blood into each of the two 4 mL Lithium-Heparin blood collection tubes.

Transport to the laboratory refrigerated.

Collect whole blood directly into a Lithium-Heparin blood collection tube (minimum volume 5 mL) and gently mix by inverting the tube several times to dissolve the heparin.

Alternately, collect whole blood directly into two Lithium-Heparin blood collection tube (minimum volume 3 mL into each) and gently mix by inverting the tubes several times to dissolve the heparin.

Collect by venipuncture only - DO NOT collect via line. 

Important:  Lithium-Heparin tube should be at room temperature (17-25 degrees Centigrade) at the time of blood collection.

Blood drawn into Lithium-Heparin tube must be held at room temperature (17-25 degrees Centigrade) for 15 minutes.  Transport to the laboratory refrigerated (2-8 degrees Centigrade).

Lithium-Heparin tube must not remain at room temperature for more than 3 hours after collection.  Refrigerate specimens during transport. Refrigerated specimen must be received into the laboratory within 48 hours from time of collection.

Underfilled Lithium-Heparin tube (below 5 mL) or (below 3mL in each). Refrigerated Lithium-Heparin tube received in lab after 48 hours from the time of collection.  Lithium-Heparin tube not refrigerated within 3 hours of collection. Specimen container unlabeled or labeled incorrectly. No date/time of collection or collector completed.

3 - 5 days

Chemiluminescence immunoassay

Clinical Microbiology Laboratory

QFT, QFT Plus

QFT 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 diagnositic evaluations.

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The QuantiFERON® TB Gold Plus (in Tube) assay is intended for use as an aid in diagnosis of TB infection.

This test uses a peptide cocktail of CD4+ and CD8+ T cell antigens to stimulate cells in whole blood.  Detection of interferon-gamma is used to identify in vitro responses to these peptide antigens that are associated with Mycobacterium tuberculosis infection.

A negative result suggests that M. tuberculosis infection is unlikely.  However, in patients with high suspicion of exposure, a negative test should be repeated on a new sample.

A positive result indicates an interferon-gamma response to M. tuberculosis antigens, suggesting infection with M. tuberculosis.

Positive results in patients at low-risk for tuberculosis should be interpreted with caution and repeat testing on a new sample is advised.  If repeat testing is positive, treatment may be indicated.  Consult Infectious Disease Services for further recommendations.

False positive results may occur in patients with prior infection with M. marinum, M. szulgai, or M. kansasii.

For an indeterminate result, the likelihood of determining infection with M. tuberculosis cannot be determined.  If clinically indicated, repeat testing on a new sample is advised.

Diagnosing or excluding tuberculosis disease, and assessing the probability of LTBI, requires a combination of epidemiological, historical, medical, and diagnostic findings that should be considered when interpreting QFT-Plus results.  See general guidance on the diagnosis and treatment of TB disease and LTBI https://www.cdc.gov/tb/publications/guidelines/default.htm.

*Special pre-approved events require direct draw into the four QFT-Plus blood collection tubes. Collect 1 mL of blood by venipuncture directly into each QFT-Plus blood collection tubes. The black mark on the side of each tube indicates the appropriate fill volume. Under-or-over filling of tubes outside this fill volume may lead to erroneous results.

If a "butterfly needle" is being used to collect blood, a "purge" tube should be used to ensure that the tubing is filled with blood prior to the QFT-Plus blood collection tubes being used.

Immediately after filling the tubes, shake them ten (10) times just firmly enough to make sure the entire inner surface of the tube is coated with blood. This will dissolve any antigens on the tube walls. Avoid over vigorous shaking as this may lead to gel disruption.

Following filling and shaking, the tubes must be transferred to an incubator within 16 hours of collection. Prior to incubation, maintain tubes at room temperature.