OTHER TEST REQUEST NAME:
Inteferon Gamma Production
Quantiferon TB Gold (QFT)
Interferon-gamma Release Assay (IGRA)
TEST COMPOSITION :
An indirect test for Mycobacterium tuberculosis that can cause TB infection. It detects inteferon gamma used to identify in vitro responses to peptide antigens (ESAT-6, CFP-10 and TB7.7[p4]) that are associated with the disease
SPECIAL INSTRUCTIONS/PATIENT PREPARATIONS:
No patient preparation necessary.
HPD Branches/Send In Clients:
Request sample collection container from Warehouse 1 day prior to blood extraction.
• Nil Tube (Gray cap with white ring)
• TB1 Antigen Tube (Green cap with white ring)
• TB2 Antigen Tube (Yellow cap with white ring)
• Mitogen Tube (Purple cap with white ring)
SPECIMEN AND VOLUME REQUIREMENT
Note: Follow tube manufacturer recommendation.:
1 mL Whole Blood for each tube
ALTERNATIVE SPECIMEN AND VOLUME REQUIREMENT:
(2) Two pieces 4 mL Heparinized Whole Blood (Lithium Heparin ONLY) OR
(4) Four pieces 2 mL Heparinized Whole Blood (Lithium Heparin ONLY)
• ROOM TEMPERATURE (15-25°C) :
• REFRIGERATED TEMPERATURE (2-8°C) :
• FREEZER TEMPERATURE (-20°C) :
Transport specimen at 17-27°C (room temperature) within 16 hours of collection
Do not refrigerate the blood
• Insufficient volume of blood to anticoagulant
• Over filling of Collection tubes
• Vigorous shaking of tubes that may cause gel disruption.
• Improperly labeled specimens
• Specimen stored/transported outside the temperature range
Wednesday and Saturday
CUT OFF TIME:
Tuesday, 6:00 PM
Friday, 6:00 PM
TAT/RELEASING OF RESULTS:
FREQUENTLY ASKED QUESTIONS (FAQS):
What is QFT?
QuantiFERON-TB Gold is an in-vitro laboratory test for detection of immune responses to tuberculosis (TB) infection in whole blood. It is used as a diagnostic aid for M. tuberculosis complex infection, whether active tuberculosis disease or latent tuberculosis infection (LTBI), and is intended for use in conjuction with risk assessment, radiography, and other medical and diagnostic evaluations
Can QFT distinguish between active TB and LTBI?
QFT cannot distinguish between active TB and LTBI. Anyone testing positive should be assessed for active TB using clinical examination and/or a chest radiograph.
What is the minimum time necessary to wait between exposure to M. tuberculosis and QFT testing?
The CDC guidelines on the use of QFT recommend that recent contacts who test QFT NEGATIVE soon after the end of exposure be retested 8-10 weeks later – similar to the recommendations for the Tuberculin Skin Test (TST). Many other national guidelines recommend a similar approach.
What is the specificity and sensitivity of QuantiFERON-TB Gold In-Tube?
The specificity of QuantiFERON-TB Gold In-Tube has consistently shown to be >99% in low risk individuals. On the other hand, the sensitivity is as high as 92% in individuals with active disease, but varies depending on the setting and extent of TB disease.
Can Interferon Gamma Release Assay (IGRA) tests be used for infants and children?
Evidence shows that QFT performs as well in children as it does in adults and there is no apparent loss of performance in children under 5 years.QFT has been shown to be effective in children less than 6 months of age and in children with bacteriologically confirmed TB.
How are QFT results interpreted?
A positive result suggests that current M. tuberculosis infection is likely. The result does not differentiate between recently acquired or old infection, or between LTBI and active TB. A negative QFT result suggests that M. tuberculosis infection is unlikely but cannot be excluded especially when illness is consistent with tuberculosis disease or the likelihood of progression to disease is increased (ex. Because of immune suppression). An indeterminate QFT result suggests that TB infection can neither be excluded nor confirmed and that test should be repeated. However, an indeterminate result is meaningful, suggesting patient’s immune suppression.
Are the results affected by pregnancy?
No definitive information is currently available on whether the results of IGRA tests are affected by pregnancy. However, there is no reason to suspect that QFT would be affected any more than in the TST.