QuantiFERON-TB Gold Plus, Blood

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Test Code: QGOLD

Overview
Ordering
Specimen
Performing
Clinical/Interpretive
Contacts
Coding

Synonyms/Keywords

Quantiferon, Tuberculosis, TB, QGOLD, Interferon gamma release assay, IGRA

Test Components

QuantiFERON-TB Gold Plus is a fourth generation interferon (IFN)-gamma release assay (IGRA) that indirectly detects Mycobacterium tuberculosis infection. It is a chemiluminescence immunoassay that measures the interferon-gamma as a result of cell-mediated immune response to TB-specific antigens.

Useful For

Aids in the detection of latent and active Mycobacterium tuberculosis infection. This test is intended for use in conjunction with other clinical assessments for M tuberculosis.

Specimen Requirements

Fasting Required	Specimen Type	Preferred Container/Tube	Acceptable Container/Tube	Specimen Volume	Specimen Minimum Volume (allows for 1 repeat)	Pediatric Minimum Volume (no repeat)
No	Whole Blood	ONLY Green Top Lithium Heparin Tube (GTT)	Green Top Lithium Heparin Tube (GTT)	6 mL	5 mL	Not performed on children <2 years of age

Collection Processing Instructions

Specimens can be collected ONLY MONDAY through FRIDAY for the required timely processing of specimens.

Collect 6 mL (minimum 5 mL) of blood in a lithium heparin green top tube (GTT). Thoroughly mix the specimen by slowly inverting the tube at least 10 times to dissolve the heparin. Inversion should be performed slowly enough to ensure the airspace reaches the opposite end of the tube each time.

Label tube with the DATE and TIME of collection.

Allow the blood drawn into the lithium-heparin tube to remain at room temperature between 15 minutes to 3 hours after blood collection.

After a minimum of 15 minutes at room temperature, refrigerate the specimen within three hours of collection and transport it to Marshfield Labs the same day of collection.

Specimen Stability Information

Specimen Type	Temperature	Time
Lithium Heparin Blood	Refrigerated	36 hours

Rejection Criteria

Blood collected in lithium heparin gel tubes

Anticoagulant tubes other than lithium heparin

Less than 5 mL whole blood collected

Samples stored beyond the time and temperature of stability

Performing Laboratory Information

Performing Location	Day(s) Test Performed	Analytical Time	Methodology/Instrumentation
Marshfield	Monday through Friday*	2-7 days	Chemiluminescence immunoassay (Liaison XL)
* Samples can ONLY be collected and received in the lab MONDAY through FRIDAY.

Test Information

The QuantiFERON-TB Gold Plus assay is performed in a four-tube format. Mitogen and Nil tubes serve as positive and negative controls for the test. The TB Antigen Tube 1 (TB1) contains CD4 T cell stimulating ESAT-6 and CFP-10 antigens. TB Antigen Tube 2 (TB2) contains the same CD4 antigens of TB1 and additional CD8 antigens.

Individuals infected with Mycobacterium kansasii, Mycobacterium szulgai, or Mycobacterium marinum may test positive by QuantiFERON-TB Gold Plus due to measurable response to the ESAT-6 and CFP-10 proteins.

This test may be used in place of the tuberculin skin test and will not give positive results in BCG-vaccinated individuals.

This test cannot differentiate between latent and active TB.

This test will not be performed on children <2 years of age. In these circumstances, a Tuberculin Skin Test (TST) should be performed. For pediatric patients > 2 years of age in which the minimum amount of blood for QGOLD can not be collected, specimens will automatically be forwarded to Quest Diagnostics for the Interferon Gamma Release Assay (IGRA) test using a MISC test code.

Reference Range Information

Performing Location	Reference Range
Marshfield	Negative

Interpretation

This is a qualitative test reported as Negative, Positive, or Indeterminate based on the interpretation of four assay tube values. Numeric values of these tubes will also be reported.

• NIL: This value represents nonspecific reactivity produced by the patient specimen.

• MITOGEN minus NIL (MITOGEN-NIL): This value serves as the positive control for the patient specimen, demonstrating successful lymphocyte activity.

• TB1 minus NIL (TB1-NIL): This tube specifically detects CD4+ lymphocyte reactivity, specifically stimulated by the TB1 antigens.

• TB2 minus NIL (TB2-NIL): This tube detects both CD4+ and CD8+ lymphocyte reactivity stimulated by TB2 antigens.

Table: Guidance for the Interpretation of QGOLD Results

Nil (IU/mL)	TB1 minus Nil (IU/mL)	TB2 minus Nil (IU/mL)	Mitogen minus Nil (mL)	QuantiFERON-TB Gold Plus Result	Interpretation
≤ 8.0	≥ 0.35 and ≥ 25% of the Nil	Any	Any	Positive	M. tuberculosis infection likely
	Any	≥ 0.35 and ≥ 25% of the Nil	Any	Positive	M. tuberculosis infection likely
	< 0.35 OR ≥ 0.35 and <25% of Nil	< 0.35 OR ≥ 0.35 and <25% of Nil	≥ 0.5	Negative	M. tuberculosis infection NOT likely
	< 0.35 OR ≥ 0.35 and <25% of Nil	< 0.35 OR ≥ 0.35 and <25% of Nil	< 0.5	Indeterminate	Likelihood of M. tuberculosis infection cannot be determined
≥ 8.0	Any			Indeterminate

For more information regarding QuantiFERON-TB gold testing, including follow-up to positive results, see guidance from the Wisconsin Department of Health Services - Wisconsin Tuberculosis Program.

Outreach CPTs

CPT	Modifier (if needed)	Quantity	Description	Comments
86480		1	Tuberculosis Test, cell mediated response, gamma interferon

Synonyms/Keywords

Quantiferon, Tuberculosis, TB, QGOLD, Interferon gamma release assay, IGRA

Test Components

Ordering Applications

Ordering Application	Description
Cerner	QuantiFERON-TB Gold

If the ordering application you are looking for is not listed, contact your local laboratory for assistance.

Specimen Requirements

Fasting Required	Specimen Type	Preferred Container/Tube	Acceptable Container/Tube	Specimen Volume	Specimen Minimum Volume (allows for 1 repeat)	Pediatric Minimum Volume (no repeat)
No	Whole Blood	ONLY Green Top Lithium Heparin Tube (GTT)	Green Top Lithium Heparin Tube (GTT)	6 mL	5 mL	Not performed on children <2 years of age

Collection Processing

Specimens can be collected ONLY MONDAY through FRIDAY for the required timely processing of specimens.

Label tube with the DATE and TIME of collection.

Allow the blood drawn into the lithium-heparin tube to remain at room temperature between 15 minutes to 3 hours after blood collection.

After a minimum of 15 minutes at room temperature, refrigerate the specimen within three hours of collection and transport it to Marshfield Labs the same day of collection.

Specimen Stability Information

Specimen Type	Temperature	Time
Lithium Heparin Blood	Refrigerated	36 hours

Rejection Criteria

Blood collected in lithium heparin gel tubes

Anticoagulant tubes other than lithium heparin

Less than 5 mL whole blood collected

Samples stored beyond the time and temperature of stability

Useful For

Aids in the detection of latent and active Mycobacterium tuberculosis infection. This test is intended for use in conjunction with other clinical assessments for M tuberculosis.

Test Components

Reference Range Information

Performing Location	Reference Range
Marshfield	Negative

Interpretation

This is a qualitative test reported as Negative, Positive, or Indeterminate based on the interpretation of four assay tube values. Numeric values of these tubes will also be reported.

• NIL: This value represents nonspecific reactivity produced by the patient specimen.

• MITOGEN minus NIL (MITOGEN-NIL): This value serves as the positive control for the patient specimen, demonstrating successful lymphocyte activity.

• TB1 minus NIL (TB1-NIL): This tube specifically detects CD4+ lymphocyte reactivity, specifically stimulated by the TB1 antigens.

• TB2 minus NIL (TB2-NIL): This tube detects both CD4+ and CD8+ lymphocyte reactivity stimulated by TB2 antigens.

Table: Guidance for the Interpretation of QGOLD Results

Nil (IU/mL)	TB1 minus Nil (IU/mL)	TB2 minus Nil (IU/mL)	Mitogen minus Nil (mL)	QuantiFERON-TB Gold Plus Result	Interpretation
≤ 8.0	≥ 0.35 and ≥ 25% of the Nil	Any	Any	Positive	M. tuberculosis infection likely
	Any	≥ 0.35 and ≥ 25% of the Nil	Any	Positive	M. tuberculosis infection likely
	< 0.35 OR ≥ 0.35 and <25% of Nil	< 0.35 OR ≥ 0.35 and <25% of Nil	≥ 0.5	Negative	M. tuberculosis infection NOT likely
	< 0.35 OR ≥ 0.35 and <25% of Nil	< 0.35 OR ≥ 0.35 and <25% of Nil	< 0.5	Indeterminate	Likelihood of M. tuberculosis infection cannot be determined
≥ 8.0	Any			Indeterminate

For more information regarding QuantiFERON-TB gold testing, including follow-up to positive results, see guidance from the Wisconsin Department of Health Services - Wisconsin Tuberculosis Program.

For more information visit:

http://labtestsonline.org

Performing Laboratory Information

Performing Location	Day(s) Test Performed	Analytical Time	Methodology/Instrumentation
Marshfield	Monday through Friday*	2-7 days	Chemiluminescence immunoassay (Liaison XL)
* Samples can ONLY be collected and received in the lab MONDAY through FRIDAY.

For billing questions, see Contacts

Outreach CPTs

CPT	Modifier (if needed)	Quantity	Description	Comments
86480		1	Tuberculosis Test, cell mediated response, gamma interferon

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For most current information refer to the Marshfield Laboratory online reference manual.

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26598 QuantiFERON-TB Gold Plus, Blood