Quantiferon Gold

QTB/QTB2

Quantiferon Gold, TB Gold, TB, Tuberculosis, QBT2, Quantiferion Gold Plus

6 ml Lithium Heparin Tube:

Phlebotomy Specimen Collection Instructions
 
Phlebotomist will collect a 6-ml Lithium-Heparin vacutainer (green) by venipuncture method.

• Mix, do not centrifuge
• Label with appropriate patient information and date/time/phlebotomist’s initials.
• Deliver to Microbiology
  • Specimen can remain at room temperature up to 12 hours
  • If transport delay is anticipated, specimen should be stored at room temperature for 15 minutes to 3 hours and then refrigerator temperature for up to 48 hours.
• Contact Microbiology if additional instructions or information is needed.
• 6-ml Lithium-heparin tubes are available from laboratory phlebotomy department.Smaller vacutainer tubes are not acceptable.
• 

6 mL lithium Heparin Vacutainer tube (full)

Microbiology Specimen Processing.
Performed by MICROBIOLOGY LAB ASSISTANTS:

• Lithium Heparin tube should be at room temperature before aliquoting to QFT tubes.
• Remix the tube before aliquoting.
• Under the biohood, carefully remove all 4 caps and set behind appropriate QFT tube.
• Using plastic pipette, add whole blood from the Lithium Heparin tube to the fill line on each of the tubes QTB Tubes.1 ml per tube.
• Replace each colored cap on the appropriately colored tube.
• Mix tubes immediately after filling.Firmly shake 10 times to make sure the entire inner surface of the tube is coated with blood so that it is mixed well with the antigen coating on the sides of the tubes.
• Within 2 hours, place the tubes into the 37°C incubator.Incubate 16-24 hours.
• Remove from incubator and place in rack by Bench 3.Stable for up to 3 days in refrigerator or room temperature.CLS will centrifuge just before testing.
• 

Place in 37⁰ C incubator within 16 hours of collection time.,

M-F

2-3 days

If either or both the TB1-Nil or the TB2-Nil results are

• < =0.35 IU/mL = Negative
• > 0.35 IU/mL = Positive

Interpretation:
Diagnosing or excluding tuberculosis disease, and assessing the probability of latent TB infection requires a combination of epidemiological, historical, medical, and diagnostic findings that should be taken into account when interpreting Quantiferon-TB Gold Plus results.

A Positive result suggests that TB infection is likely – either active or latent.

• Per the package insert, it is prudent to confirm a positive QFT-Plus test by the same or alternate method before starting therapy if M.tuberculosis complex infection is not suspected.
• Results just above or just below the cut off thresholds can switch back and forth between a positive and negative interpretation.
  • Some facilities use a broader Borderline range and suggest having these patients retested in 4-8 weeks.
• If TB1-Nil or TB2-Nil results are both less than 0.35 IU/mL suggests that TB infection is unlikely.
• Indeterminate result suggests the need for further investigation or repeat testing.

Since the QFT-Plus test is based on the response of lymphocytes in the blood, it would follow that persons in an immunocompromised state may not have an adequate reaction to this test.  The QFT-Plus has built-in controls that assess the adequacy of the patient’s cells to show an immune reaction.  Below are listed the 4 reactions tested in the QFT-Plus test:

• The TB1 tube contains peptide antigens ESAT-6 and CFP-10 from the MTB-complex which normally produce a cell-mediated immune response.The TB1 tube measures the cytokine IFN-gamma secreted by CD4+ T lymphocyte cells.
• The TB2 tube also contains the ESAT-6 and CFP-10 antigens which produce a cell-mediated response from the CD4+ T cells.In addition, the TB2 tube contains other peptides targeted to induce an immune response from the CD8+ cytotoxic T lymphocytes.
  • The CD8+ T cells normally participate in the host (patient’s) defense to MTB by producing interferon-gamma and other factors which activate macrophages to suppress growth of MTB in the patient, kill infected cells, or directly lyse intracellular MTB.
• 2 types of Indeterminate Results
  • A low response to Mitogen (less than 0.5 IU/mL) will produce an Indeterminate result.  The Mitogen tube is a specimen control reaction tube to ensure the patient has an adequate ability to generate an immune response.  This low Mitogen response is most often associated with reduced lymphocyte activity due to:
    • low numbers of lymphocytes or
    • inability of the patient’s lymphocytes to generate the interferon-gamma immune response because of
      • immune-modulating therapies
      • recent patient illness
      • compromised immune status or
      • improper specimen handling
    • When patient results are Indeterminate due to a low Mitogen result, a comment is attached to the result:
      • “Possible impaired cellular immune response.
      •  
  • Elevated Nil values greater than 8.0 IU/mL will produce a test interpretation of Indeterminate.   The Nil tube measures circulating background interferon-gamma antibody, such as heterophile antibody. This value is subtracted from the TB1, TB2 and the Mitogen tests.  High Nil values are often seen in various autoimmune diseases and conditions.  When result is Indeterminate because the Nil value is too high, the following comment is attached to the result:
• “Indeterminate result due to high levels of non-specific background circulating antibod

 

QuantiFERON—TB Gold Plus (QFT-Plus) uses:

• Quantiferon-TB Gold Plus (QFT-Plus) is a blood test used as an aid in diagnosing Mycobacteria tuberculosis.
• The CDC recommendations state that the QFT-Plus may be used in place of a tuberculin skin test (TST) in all situations in which CDC recommends the TST be used as an aid in diagnosing M.tuberculosis infection.
• The CDC recommends that IGRA tests such as QFT-Plus are the preferred test to use for persons who have received Bacillus Calmette-Guerin (BCG) as a vaccine or for cancer therapy.

 
QuantiFERON—TB Gold Plus (QFT-Plus) test measures the amount of interferon-gamma (IFN-gamma) produced when the lymphocytes in the blood are stimulated by ESAT-6 and CFP-10 proteins which are part of the test system tubes.  An immune response to these specific protein antigens is associated with Mycobacteria tuberculosis infection. The QFT-Plus test is an “Interferon-Gamma Release Assay” (IGRA) that can be performed on a single whole blood collection however, like the historically used TST, IGRA testing cannot distinguish between active tuberculosis and latent, asymptomatic tuberculosis.