Quantiferon (TB) Testing (QFT)

Microbiologist                  Claudia Rogers, BS MT (ASCP)             (307) 777-6061

Microbiologist                         Beth White, BS                                 (307) 777-6063

 

The QuantiFERON-TB test (QFT) was approved by FDA as an aid for detecting latent Mycobacterium tuberculosis infection. This test is an in vitro diagnostic aid that measures a component of cell-mediated immune reactivity to M. tuberculosis. The test is based on the quantification of interferon-gamma  released from sensitized lymphocytes in whole blood incubated overnight with purified protein derivative (PPD) from M. tuberculosis and control antigens.

 

 

 

TYPE OF TEST

Interferon-Gamma Release Assay (IGRA) is a whole-blood EIA test to detect in vitro responses to peptide antigens simulating mycobacterial proteins. Results can aid in detection of Mycobacterium tuberculosis infection.

SPECIMEN REQUIREMENTS

Submit a set of 3 specialized QFT heparin tubes provided by the lab: one Gray top - Nil tube, one Red top – TB antigen tube, and one Purple top – Mitogen control tube. Collection procedure is very specific and detailed. Refer to the QFT Collection Protocol in the section “Microbiology Collection and Submission Protocols” on this web site. 

Specimens must be incubated at 37° within 16 hours of the draw for 16-24 hours.  If incubation was performed at the site, specimens must be received at WPHL within 3 days of incubation.  The specimen must be received by Friday of that week. 

Specimens may be incubated at WPHL instead of on site, if delivered to the lab within 16 hours of the draw on Monday through Thursday.  Contact the WPHL for further instructions.

SHIPPING REQUIREMENTS

Tubes should be held and transported at room temperature.  Do not refrigerate or place on ice.  Samples must be submitted with a completed QFT Requisition form, including the date, time drawn and incubation period.  Place tubes in biohazard bag, with QFT request form in the outside pocket.  Package in mailers provided by WPHL or comparable approved shipping container.  Ship as diagnostic specimen following postal or carrier shipping regulations.

DAYS TEST PERFORMED

Tuesday and Thursday.

RESULTS AVAILABLE

Results will be mailed upon completion. 

REPORTING & INTERPRETATION

Results are reported as:

TB Ag-Nil RESULT: ______ NEGATIVE - <0.35 (M. tuberculosis infection NOT likely); POSITIVE - > 0.35 (M. tuberculosis infection likely); INDETERMINATE – indicates an uncertain likelihood of M. tuberculosis infection OR incorrect specimen handling/incubation.   Repeat testing recommended in 6 weeks.   All results of Quantiferon TB Gold testing should be interpreted in the context of patient’s likelihood of prior tuberculosis exposure.

ADDITIONAL COMMENTS

Heparin tubes fill very slowly. Allow tubes to stay on needle for 2-3 seconds after the tube appears to have filled completely.  Required fill is between a width of the black line below the line and a width of the black line above it.

 

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