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Test Code QTB/LAB1232191 QuantiFERON Gold

Performing Laboratory

Asante Rogue Regional Medical Center

Specimen Requirements

QuantiFERON Gold Blood Collection Tubes – Obtain collection tubes from RRMC Central Processing

Specimen Minimum/Maximum Volume

1 mL of blood into each of 3 Quantiferon tubes.

Minimum volume is 0.8 mL per tube

Maximum volume is 1.2 mL per tube

 

QuantiFERON Collection and Processing Instructions

Specimen Transport Temperature and Stability

  1. Collect 1 mL of blood into each of the 3 tubes - Standard Altitude: QuantiFERON-QTB Gold In-Tube Collection Kit (T628)
    • Tubes fill slowly.
    • Use of a syringe may ensure correct blood volume.
    • When the tube is upright, blood must meet the small black mark on the label.
    • If a butterfly needle is used, first collect other required tubes or use a “purge” tube to remove the air and then proceed with collecting the QTB tubes.
  2. Immediately shake the tubes firmly ten times in an up and down motion, firmly enough to ensure the entire surface of the tube is coated with blood. This action will dissolve antigens on the tube walls.

    • Over-energetic shaking may cause gel disruption and could lead to aberrant results.
  3. Label tubes such that the “Quantiferon” band and entire specimen volume are visible.
  4. Maintain tubes at ambient temperature until incubation.
    • Incubation MUST be started within 16 hours of collection
    • It is recommended that incubation starts as soon as possible
    • Send to RRMC Central Processing as soon as possible.
  5. Invert tubes for 5 seconds immediately before incubation.
  6. Incubate all 3 tubes upright at 37° C for 16-24 hours.
    • DO NOT use water bath for incubation
    • Improper incubation may cause erroneous results.
  7. Centrifuge tubes for 15 minutes at 3000 RCF (g).
  8. Place all 3 tubes together in the QTB Transport bag, send to RRMC Special Chemistry Department.
  9. Store refrigerated (2-8oC). Stable 28 days refrigerated.

Reasons for Rejection

1. Lacking Two Patient Identifiers

2. Specimen rejected for not following collection guidelines

Day(s) Test Set Up

Test Batched: Tuesday and Friday, AM shift

Performing Department

Special Chemistry

Methodology

Ezyme-linked Immunosorbent Assay (ELISA)

Additional Information

Clinical Information:

 

Tuberculosis is a communicable disease caused by infection with M. tuberculosis complex organisms. A newly infected individual can become ill from tuberculosis within weeks to months, or can remain latently infected for years. Latent tuberculosis infection (LTBI) is a non-communicable asymptomatic condition, persisting in some who might develop tuberculosis disease months or years later. The main purpose of diagnosing LTBI is to consider medical treatment for preventing tuberculosis disease. The TST is a subjective test that can be falsely positive in individuals who are sensitive to tuberculin and have a positive TST result after being vaccinated with the bacilli Calmette-Guérin (BCG). In addition, some individuals may have weakened immune functions due to other conditions and do not respond to tuberculin.

 

The QuantiFERON®-TB Gold (QFT) test is a test for cell-mediated immune responses to peptide antigens that simulate mycobacterial proteins. These proteins, ESAT-6, CFP-10 and TB7.7(p4), are absent from all BCG strains and from most non-tuberculosis mycobacteria with the exception of M. kansasii, M. szulgai, and M. marinum. Individuals infected with M. tuberculosis complex organisms (M. tuberculosis, M. bovis, M. africanum, M. microti, M. canetti) usually have lymphocytes that recognize these mycobacterial antigens. This recognition process involves the secretion of cytokine, IFN- γ. The detection and quantification of IFN- γ forms the basis of the QFT test. The QFT in-tube is an indirect in-vitro diagnostic test intended to aid in the diagnosis of latent tuberculosis caused by Mycobacterium tuberculosis. This is an FDA approved method using a cocktail simulating ESAT-6, CFP-10, and TB7.7 (p4) proteins to stimulate cells in heparinized whole blood. Detection of interferon-γ (IFN- γ) by ELISA is used to identify in-vitro responses to these peptide antigens that are associated with Mycobacterium tuberculosis infection.

 

Interpretation of Results:

 

This is a qualitative test. The TB Antigen (Ag)-nil IU/mL value should not be used to differentiate active from latent disease or to monitor disease progression or response to therapy.

Diagnosis or exclusion of tuberculosis (TB) and assessing the probability of latent tuberculosis infection (LTBI), require a combination of epidemiologic, historical, clinical, radiologic, and additional laboratory findings (eg, mycobacterial smear and/or culture) be taken into account when interpreting QuantiFERON-TB Gold results.

The nil value is used to determine the background, circulating interferon-gamma level in the patient. For the QuantiFERON-TB Gold test to be valid, the nil value must be less than or equal to 8.0 IU/mL.

 

The mitogen minus nil value is used to assure that the patient is able to produce an interferon-gamma response to a universal stimulant (phytohemagglutinin). For the QuantiFERON-TB Gold test to be valid, the mitogen value must be at least 0.5 IU/mL higher than the nil value.

 

The QuantiFERON-TB Gold test is considered positive if the interferon-gamma response in the TB antigen minus nil value is at least 0.35 IU/mL.

 

Limitations

 

False-positive QuantiFERON-TB Gold results may occur due to improper preanalytical processing of the QuantiFERON-TB Gold tubes, prior infection with certain other mycobacteria (eg, Mycobacterium marinum, M kansasii, M szulgai) or biologic variability. Positive results should be confirmed with other clinical, exposure, and laboratory findings.

 

TB antigen minus nil values between 0.35 IU/mL and 1.1 IU/mL may represent false-positive results in individuals at low risk for latent tuberculosis infection (LTBI). Repeat testing on a new specimen or testing for LTBI by an alternative method is recommended.

 

A negative QuantiFERON-TB Gold result does not preclude the possibility of Mycobacterium tuberculosis infection or tuberculosis disease. Falsely negative results can be due to the stage of infection, co-morbid conditions that affect immune functions, other individual immunological factors, improper blood sample collection or handling of the specimen affecting lymphocyte function. Blood must be incubated with stimulation antigens within 16 hours of collection. Delay in incubation may cause false-negative or indeterminate results.

 

The effect of lymphocyte count on reliability is unknown. Lymphocyte counts may vary from person to person. The minimum number required for a reliable result has not been established.

 

The performance of QuantiFERON-TB Gold has not been evaluated in specimens from:

  • Individuals with impaired or altered immune functions (HIV infections, transplant patients, those receiving immunosuppressive drugs such as corticosteroids) and those with other clinical conditions (eg, diabetes, hematological disorders)
  • Individuals younger than 17-years old
  • Pregnant women

The most recent Centers for Disease Control and Prevention recommendations for diagnosis of M tuberculosis infections (including disease) and selecting persons for testing can be found at www.cdc.gov/nchstp/tb.

References

  1. Package insert: QuantiFeron®-TB Gold (QFT®) ELISA. The Whole Blood IFN-γ test measuring responses to ESAT-6, CFP-10, and TB7.7(p4) peptide antigens.  1075116 Rev.03, March 2016.
  2. Rogue Regional Medical Center Laboratory method validation studies performed October 2017.
  3. Centers for Disease Control and Prevention. Updated Guidelines for Using Interferon Gamma Release Assays to Detect Mycobacterium tuberculosis Infection --- United States, 2010. MMWR June 25, 2010.  59(RR05);1-25.

4.    “QuantiFERON-TB Gold In-Tube for Detection of Latent Tuberculosis, Blood.”  

       QFT3 - Overview: QuantiFERON-TB Gold In-Tube for Detection of Latent    

       Tuberculosis, Blood, Nov. 2017, www.mayomedicallaboratories.com/test-            

       catalog/Overview/38510.

Test Classification and CPT Coding

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions.

CPT code : 86480

LOINC

TEST ORDER NAME:

 QuantiFERON-TB Gold In-Tube  71775-1

 

TEST RESULT NAME:

QuantiFERON-TB Gold Result    71773-6

TB Ag minus Nil Result                64084-7

Mitogen minus Nil Result             71774-4

Nil Result                                     71776-9

Billing Code

3020119