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Testing Results
IMPORTANT! Pre-approval needed from state or local health department. Local or State Health Department. Send approval to or call (402) 559-9444.

NPHL has moved to an electronic ordering system, NUlirt, and it is now the preferred method to order all tests. Once ordered, print a "batch list" (see NUlirt Guide).

Forms Required - Nulirt batch list or NPHL Test Request Form (completed in entirety) must accompany the specimen to include the following information: symptoms and date of onset, pregnancy status, travel and vaccine history. Testing will not be performed without all required information.


  Test: TB Interferon Antigen Response  
  Synonym: TB Quant, IGRA, Interferon Gamma Release Assay 
  Method: Enzyme-linked immunosorbant assay (ELISA)  
  Availability: Routine testing is performed on Tuesday and Friday. Samples require an incubation period of at least 16 hours before processing for testing. Samples received by 3pm Monday and Thursday will usually be tested the following day but not guaranteed. Please contact client services in priority situations. Results are reported by 4 pm on Tuesday and Friday.  
  Specimen: Collect 1mL of blood by venipuncture directly into each of the QuantiFERON-TB Gold Plus (QFT-PLUS) blood collection tubes using only a vacutainer or syringe. Four tubes must be collected for each patient: gray cap tube (Nil control), green cap tube (TB1 antigen), yellow cap tube (TB2 antigen) and purple cap tube (Mitogen Control). It is recommended to draw in the order of gray, green, yellow, purple. As 1 ml tubes draw blood relatively slowly, keep the tube on the needle for 2-3 seconds once the tube appears to have completed filling. This will ensure the correct volume is drawn. If a “butterfly needle” is being used to collect blood, use a "purge tube" to ensure that the tubing is filled with blood prior to use of the QFT-Plus blood collection tubes. The black indicator line on the side of the tube indicates the correct fill volume; the tubes must not be filled above or below this line. If one tube is a short draw tube, the one tube can be redrawn immediately. All four tubes do not need to be redrawn.
Mix the tubes after the draw by shaking 10 times, firmly enough to ensure that the entire inner surface of each tube is coated with blood to solubilize antigens on tube walls. Over-energetic shaking may cause gel disruption and could lead to aberrant results.

The collection date and time is required on the specimen tubes. If adding a barcode label, please do not cover the top of the TB Gold IT color coded label which is necessary for the lab to identify tube type. Transport immediately and store at room (ambient) temperature. DO NOT CENTRIFUGE, REFRIGERATE, PLACE ON ICE, OR FREEZE THE BLOOD SAMPLES.  
  Collection Device: QuantiFERON-TB Gold Plus (QFT-PLUS) blood collection tubes

Specimen Labeling:Test subject to CLIA regulations and required 2 patient identifiers on specimen container and requisition forms. If using bar codes do not cover the portion of the label with the black fill line. Indicate if specimens are incubated prior to transport to lab.  
  Volume: See above  
  Storage/Transport: Prior to and during shipment: Specimens must be sent to the laboratory immediately so they can be processed within 16 hours of collection. See above/below instructions.

Shipping instructions, including specimen-handling requirements during transport: Specimens can be received in the Microbiology Laboratory at any time 24 hrs/day; 7 days/week. Please contact client services at (866) 290-1406 if courier service is needed for outpatient specimens.

Specimens may be incubated on-site before submission: 37°C for 16-24 hours. Label tubes as "incubated". Once incubated, un-centrifuged tubes are acceptable up to 3 days post incubation at 4°-27°C. For longer transport, centrifuge tubes for 15 minutes at 3000g and send refrigerated.

Package and ship as UN3373 Category B, Biological Substance. Place in biohazard bag with absorbent material. Transport by NPHL ground courier (NPHL brown shipper not required). If courier not available, contact Client Services to arrange pickup.
See instructions and shipping address:  
  Unacceptable: Collect time and date is not recorded on specimen; use of any blood collection tubes other than the QFT-Plus blood collection tubes; samples outside the acceptable fill range (black indicator line).

Specimens incubated, not incubated within 16 hours of collection, incubated >24 hours; not received by the laboratory within 3 days (unless centrifuged), frozen, incorrectly labeled tubes.  
  Specimen Stability: Non-incubated: Ambient. Samples must be received by the lab < 16 hours after collection.

Incubated: Un-centrifuged specimens: ambient or refrigerated. Specimens must be received in the lab within 3 days after incubation. Specific incubation instructions required. If transport time after incubation will be >3 days, centrifuge sample (15 minutes at 3000g) and send refrigerated.  
  Reference Interval: Negative < 0.35 IU/ml
Positive >= 0.35 IU/ml  
  Reportable Disease: Not Reported 
  Comments: Pre-approval needed from state or local health department. Send approval to or call (402) 559-9444.

QuantiFERON-TB Gold Plus is an in vitro diagnostic test using a peptide cocktail simulating ESAT-6 and CFP-10 proteins to stimulate cells in heparinized whole blood. Detection of interferon-? (IFN-?) by enzyme-linked immunosorbent assay is used to identify in vitro responses to these peptide antigens that are associated with Mycobacterium tuberculosis infection.

QFT-Plus is an indirect test for M. tuberculosis infection (to include latent disease) and is intended for use in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations. 
  Revised: 7/11/2019 


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