FAQ - Healthcare Professionals
What is the scale of the TB problem?
The World Health Organization (WHO) estimates that more than one-third of the World's population is infected with Mycobacterium tuberculosis. Even in the developed world, TB rates are stable at best, and actually increasing in many areas. This is due to factors such as immigration, HIV and other immunosuppressive conditions.
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Is there a test for latent TB infection?
Until recently, the only way of testing for latent TB was the use of the Tuberculin Skin Test (TST). The introduction of blood based tests (i.e. Interferon Gamma Release Assays or IGRAs), such as the T-SPOT.TB test, provides a new way to diagnose latent TB infection. The T-SPOT.TB test is an in vitro diagnostic test for the detection of effector T cells that respond to stimulation with MTB specific antigens. These antigens, ESAT-6 and CFP 10 are absent from all BCG strains and from most non-tuberculosis mycobacteria. Benefits of the T-SPOT.TB test are:
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Sensitivity of 95.6%*
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Specificity of 97.1%*
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Reliable in all targeted groups, including†:
o Immunosuppressed
o Immigrants
o Health Care Workers
o TB Suspects
o TB Contacts
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Does not cross react with BCG vaccine and most common non-tuberculosis mycobacteria
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Single blood test, no repeat visit required.
*T-SPOT.TB Pivotal Clinical Study. Sensitivity of 95.6% and Specificity of 97.1% T-SPOT.TB Package Insert.
†T-SPOT.TB Pivotal Clinical Study. Results demonstrated no association with T-SPOT.TB results and immunocompromised status or BCG vaccination. T-SPOT.TB was not impacted by age. T-SPOT.TB Package Insert.
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What species of Mycobacteria will test positive with the T-SPOT®.TB test?
T-SPOT.TB produces positive results in all three TB-causing species of the Mycobacterium tuberculosis Complex; M. tuberculosis, M. bovis and M. africanum.
The antigens used in the test, ESAT-6 and CFP 10, are present in three other atypical non-tuberculosis mycobacteria; M. marinum, M. szulgai and M. kansasii. The test may produce positive results in patients infected with these three mycobacteria. The antigens used in the test are not present in all other non-tuberculosis mycobacteria.
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How many tests can I run with one T-SPOT.TB test kit?
Each 96-well plate will process 24 patient samples. The 8-well strip version of T-SPOT.TB (T-SPOT.TB 8) provides the additional flexibility of containing twelve strips with eight wells. Each strip will process 2 samples.
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Can I store blood samples?
Blood samples should be processed within 8 hours.
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What blood collection tubes do I use?
Standard blood collection tubes can be used for the T-SPOT.TB test:
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Blood samples can be collected into either sodium citrate or sodium heparin Vacutainer® CPT tubes (Becton Dickinson) and processed immediately.
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Blood samples can be collected into lithium heparin blood collection tubes with PBMCs being subsequently separated using standard separation techniques such as Ficoll-Paque™(GE Health Technologies).
For more detailed information on sample collection click here.
CPT and Vacutainer are trademarks of Becton Dickinson.
Ficoll-Paque is a trademark of GE Health Technologies.
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Can I use blood collection tubes that contain EDTA?
EDTA affects the secretion of interferon gamma. Blood collection tubes that contain this anti-coagulant cannot be used .
For more detailed information on sample collection click here.
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How do I prepare blood samples for the T-SPOT.TB test?
Blood samples are prepared using standard laboratory equipment.
For more detailed information on sample preparation click here.
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Is a standard curve required each time the test is run?
Standard curves are not required since the T-SPOT.TB test is a test that enumerates T cells.
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How do I analyze the T-SPOT.TB test results?
T-SPOT.TB test results are determined by enumerating the spots contained in the test wells. Spots can be counted directly from the well visually, using a magnifying glass, stereomicroscope or from a digital image captured from a microscope. For more detailed information click here.
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Can the finished test plates be stored for future reading?
Yes, once developed the wells contained within the completed test plates remain stable and do not need to be read immediately. The plates may be archived for retrospective quality control or re-examination for up to 12 months if kept in a dry, dark environment at room temperature.
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What approvals does the T-SPOT.TB test have?
The T-SPOT.TB test received approval from the US Food and Drug Administration (FDA) on July 30, 2008. The T-SPOT. TB test carries the CE mark which allows it to be legally placed on the market to be sold freely in the EU. Approvals have already been achieved in a number of territories outside the EU and approval is being sought in the remaining territories of commercial interest to the company.
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What is the sensitivity and specificity of the T-SPOT.TB test?
The sensitivity of T-SPOT.TB is 95.6%
The specificity of T-SPOT.TB is 97.1%
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Are there any patients that should be excluded from diagnosis with the T-SPOT.TB test?
No, T-SPOT.TB can be used in screening of any group for TB infection. T-SPOT.TB can be used for HIV-positive persons, recent contacts of TB cases, residents and employees of high risk congregate settings, chronic renal failure, and immunosuppressed patients. In addition, T-SPOT.TB can also be used as a diagnostic aid when evaluating patients suspected of having active TB disease.
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Is the T-SPOT.TB test affected by previous BCG vaccination?
Unlike the TST, there is no association with BCG vaccination and T-SPOT.TB test results. The test utilizes two M. tuberculosis specific antigens (ESAT-6 and CFP 10) that do not cross react with the BCG vaccine.
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What is the purpose of cell washing and counting in the T-SPOT.TB test?
Cell washing and counting are very important steps that improve the sensitivity and reliability of the T-SPOT.TB test.
Cell washing removes non-specific background interferon gamma (IFN-γ) that may produce interference in the test. Removal of this background IFN-γ is a not performed by ELISA methods.
Cell counting corrects for those samples where the PBMC count is low (e.g. the immunocompromised). After washing, the PBMCs (Peripheral Blood Mononuclear Cells) are counted to ensure that an adequate number of cells are used in the test.
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What data is there to support the T-SPOT.TB test in clinical use?
The body of scientific evidence continues to grow demonstrating the performance of the T-SPOT.TB test. A significant number of studies have been published worldwide in a variety of clinical and epidemiological settings, including:
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Latent TB infection and TB disease (including pulmonary and extra-pulmonary TB)
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HIV positive and negative patients
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Anti-TNF-α treated patients
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Children, adults and the elderly
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Malnourished individuals
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Renal patients undergoing dialysis
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Patients with hematological disorders
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Low prevalence countries in the developed world and high prevalence countries in the developing world
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TB contact tracing
For a summary of the T-SPOT.TB publications click here
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How simple is the T-SPOT.TB test to use?
The T-SPOT.TB test is a simplified and validated ELISpot (enzyme-linked immunospot) technique. The T-SPOT.TB test procedure uses familiar sandwich immuno assay steps.
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Where can I obtain the T-SPOT.TB test?
In North America, please contact your local Oxford Immunotec Territory Manager at 1-877-20-TSPOT (87768)
Outside of North Americal contact our UK office at 011 44 1235 442 780 or send an e-mail to info@oxfordimmunotec.com.
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What is the advantage of a blood test over the TST as it relates to the impact on healthcare resources?
There are significant costs associated with the TST to both health care systems and patients:
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A single blood test is required unlike the TST which requires the person being tested to visit the clinic at least twice. Up to one-third of people do not return to have their test read. This may result in wasted resources and potentially dangerous gaps when containing an outbreak.
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Indirect resource and time costs associated with administering and reading the skin tests are relatively high. These are compounded by the fact that the tuberculin, once opened, has to be used within a short time period leading to potential wastage of unused stock.
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Missed TB cases (false negatives and non-returners) may convert to TB disease leading to morbidity and higher costs of treating disease (including onward transmission). In addition, false positives results can lead to unnecessary antibiotic treatment and associated toxicity testing
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Why is sensitivity important for a diagnostic test for TB?
High sensitivity helps to maximize the reliability of a test for TB, ensuring that the majority of infected people are identified. This is especially important with immunocompromised patients. A test with poor sensitivity could produce high numbers of false-negative results in people who truly have disease.
In the pivotal clinical study for the T-SPOT.TB test the sensitivity was determined to be 95.6%
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