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Testing Results
IMPORTANT! Sites requesting testing must have approval from the appropriate state or local health department before submitting specimens. Approval must be sent to NPHL by email at nphl@unmc.edu or by calling (402) 559-9444.

A Special Microbiology Form must accompany the specimens. Some tests require additional forms and patient history. This will be listed below when applicable. When requested, testing will not be performed without all required information.

Please call NPHL Client Services at (402) 559-2440 or toll free at (866) 290-1406 for further clarification.

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  Test: TB Interferon Antigen Response 
  Synonym: QuantGold TB Test 
  Method: Enzyme-Linked Immunosorbent Assay 
  Availability: Weekly on Tuesday (specimens must be received by 1500 on Monday); results on same day 
  Specimen: Blood 
  Collection Device: QuantiFERON-TB Gold blood collection tubes (1 mL into each of the red cap, gray cap, and purple cap tubes), collection tubes are available from Regional Pathology Services

Collect 1 mL of blood by venipucture directly into each of the 3 tubes in the order of gray, red, and then purple. Make sure that each tube is filled to the black indicator at the 1 mL fill line. Once collected, mix the tubes by SHAKING VIGOROUSLY for 5 seconds [10 times] to ensure that the entire inner surface of the tubes have been coated with blood. 
  Volume: 3 mL total 
  Storage/Transport: Maintain specimens at room temperature (22 °C ± 5 °C) and send to the laboratory immediately so the initial processing can be completed within 16 hours of collection 
  Unacceptable: Specimens > 16 hours old; centrifuged, refrigerated, or frozen; use of any blood collection tubes other than the three tubes described; sample < or > 1 mL of blood in each tube 
  Specimen Stability: After collection, stable for 16 hours at room temperature 
  Reference Interval: < 0.35 IU/mL: NEGATIVE
Mycobacterium tuberculosis infection is unlikely.
In an individual who has symptoms, signs, or radiographic evidence of tuberculosis or is asymptomatic but at increased risk for the development of disease, a single negative test is not sufficient to exclude tuberculosis. A combination of epidemiological, historical, medical, and diagnostic findings should be taken into account when interpreting results.

≥ 0.35 IU/mL: POSITIVE
Mycobacterium tuberculosis infection is possible.
In a healthy person with a low likelihood of infection, a single positive test should not be taken as reliable evidence of tuberculosis. A combination of epidemiological, historical, medical, and diagnostic findings should be taken into account when interpreting results. A positive result does not discriminate between latent and active tuberculosis.

INDETERMINATE
Uncertain likelihood of Mycobacterium tuberculosis infection.
Suggest repeat testing in 4 to 6 weeks if clinically indicated.

(For high background interferon production) A high background interferon production does not allow an interpretation related to tuberculosis to be made.

(For lack of response to antigen stimulation) A lack of response to antigen stimulation does not allow an interpretation related to tuberculosis to be made and may indicate immunosuppression. 
  Reportable Disease: Report a positive result since this is one of the criteria used to meet the clinical case definition. 
  Comments: Although this assay is acceptable to test any age group, limited data exists for use in groups such as children younger than 5 years of age, persons recently exposed to TB, immunocompromised persons, pregnant women, and those who will be tested repeatedly.

Results from Quant-TB testing must be used in conjunction with each individual's epidemiological history, current medical status, and results of other diagnostic evaluations.

Specimens that cannot be sent for testing within 16 hours can be incubated at 37 °C ± 1 °C for 16 to 24 hours and then held between 2 °C and 27 °C for up to 3 days prior to processing. Documentation of incubation temperatures and incubation times are required with submitted incubated specimen.  
  Revised: 2/1/2012 

 

If you have questions about proper specimen collection, please call NPHL Client Services at (402) 559-2440 or toll free at (866) 290-1406.

 


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