Specimen Collection

The QuantiFERON assay-specific collection tubes (4 set), as supplied by the laboratory, must be used. No other tubes are acceptable.

The 4 tubes are:
Nil (grey cap),
TB1 antigen (green cap),
TB2 antigen (yellow cap)
Mitogen (purple cap)

Tb-Quantiferon Gold specific tube sets:

How to obtain tubes for customers both inside and outside the Auckland region

Internal

Contact Lablink x22000
Lablink is staffed for these requests Monday - Friday: 8am - 3.30pm

Tube sets are unavailable outside these hours.

External

Email your Quantiferon TB ordering form to LabLINK, lablink@adhb.govt.nz or alternatively fax LabLINK (09) 3074970

Quantiferon TB ordering forms are available from LabLINK 0800 522 7587 during business hours.

Collection procedure:

Note:

Test is invalid if:

• volume is greater or less than 1mL

• tube colour order of collect is not in right sequence

1 Collect sample according to the tube colour order of collect (grey, green, yellow, purple)

2. Collect 1mL blood (up to the black mark) into each of the Quantiferon Gold tubes supplied.

3. Mix tubes thoroughly by inversion 10 times. Ensure the entire inner surfaces of tubes are coated with blood.

4. Place patient sticker on top of the tube manufacturer label. It is paramount to leave the side of the tube clear and black mark uncovered. Without label, handwrite patient details ensuring minimum two points of ID present.

5. Send to ALSS (Specimen Services), LabPLUS

Quantiferon Gold specimen receipt at LabPLUS

The laboratory preference is to receive original blood tubes

Original blood tubes that have had no incubation or centrifugation

1. Arrival at LabPLUS must be no later than 1800 hours (6pm), Monday to Friday on the day of collection.

2. Do not refrigerate or freeze the specimens

3. Do not centrifuge the specimens

4. As soon as possible after ALSS registration, transfer to Microbiology for 37 ^o C incubation.

Original blood tubes that have been incubated and centrifuged

1. Register in ALSS and transfer to Microbiology

2. Microbiology staff will identify the blood specimens have been centrifuged and will place in the upright glass-fronted refrigerator in their specimen put-up area

Separated plasma specimens referred to LabPLUS: Protocol to follow

1. Do not refrigerate or freeze the original blood specimens prior to incubation

2. Mix tubes thoroughly by inversion 10 times. Ensure the entire inner surfaces of the tubes are coated with blood

3. Incubate within 16 hours of collection at 37oC for 16 to 24 hours

4. After centrifugation at 3000g/15 minutes, separate plasma by drawing off with a pipette into labelled daughter tubes. Ensure daughter tubes are clearly labelled as to Nil, Tb antigen and Mitogen

5. Send to LabPLUS maintaining cold chain storage (i.e. use chiller packs)

6. Register in ALSS and transfer to Microbiology

7. Microbiology staff will identify the specimens are separated plasmas and will place in the upright glass-fronted refrigerator in their specimen put-up area.

Contact Lablink for specimen tubes

Turnaround Time: Within 1 week, 3 days

Samples need a 24 hour incubation period before testing can proceed.

The ELISA test is batched and performed 3 times a week.

Equivocal results will be repeated before being reported.

Tests are not processed on weekends or statuatory holidays.

Turnaround time is 10 days.

Diagnostic Use and Interpretation

QuantiFERON-TB Gold is an in tube T-cell stimulation assay for the diagnosis of Mycobacterium tuberculosis infection, whether latent or active. It is has a similar sensitivity to the Mantoux test but is more specific.

• A positive result indicates infection with Mycobacterium tuberculosis . It can not distinguish between latent and active infection. Positive tests results can also be caused by infection with certain non-tuberculous mycobacteria ( M. kansasii , M. szulgai, and M. marinum ). Previous immunisation or treatment with M. bovis BCG strain does not cause positive test results.
• A negative Quantiferon test suggests that the patient is not infected with M. tuberculosis ; however this test should not be used to exclude active infection. Culture of appropriately collected clinical specimens remains the preferred method for diagnosisng active disease.
• An indeterminate result usually means the patient's T cells have failed to respond to the mitogen control and therefore no further interpretation of the test can be made. This may be due to inappropriate specimen handling or to underlying immunosuppression. An indeterminate result can also be produced if the patient's Nil (grey top) tube has a result >8IU/mL. The issued report will identify which mechanism has occured. In either situation, if apprpriate, the best approach is to repeat the test.
• An equivocal result lies within a laboratory established range (0.25-0.45 IU/mL Tb-Nil) where, due to the inherent assay variability; the assay qualitative interpretation may change on repeat testing. For those patients whose repeat assay result remains equivocal or changes to positive, both the initial and current specimen's Tb-Nil quantitation are additionally reported to assist with interpretation.

Contact Information

Dr Sally Roberts , Microbiologist: ext 22705 Cellphone 021 674 140
Dr Sharmini Muttaiyah , Microbiologist: ext 22700 Cellphone 021 615 892
Dr Mary de Almeida , Microbiologist: ext 22700 Cellphone 021 170 9117

Dr Matthew Blakiston , Microbiologist: contact via Lablink

For clinical interpretation contact the Clinical Microbiologist.

Specimen Transport Instructions for Referring Laboratories

Separated plasma specimens referred to LabPLUS: Protocol to follow

1. Do not refrigerate or freeze the original blood specimens prior to incubation

2. Mix tubes thoroughly by inversion 10 times. Ensure the entire inner surfaces of the tubes are coated with blood

3. Incubate within 16 hours of collection at 37oC for 16 to 24 hours

4. After centrifugation at 3000g/15 minutes, separate plasma by drawing off with a pipette into labelled daughter tubes. Ensure daughter tubes are clearly labelled as to Nil, Tb antigen and Mitogen

5. Send to LabPLUS maintaining cold chain storage (i.e. use chiller packs)

6. Register in ALSS and transfer to Microbiology

7. Microbiology staff will identify the specimens are separated plasmas and will place in the upright glass-fronted refrigerator in their specimen put-up area.

Last updated at 11:01:02 16/09/2024