About the T-SPOT.TB test
| Question | Answer |
|---|---|
| What are the advantages of the T-SPOT.TB test? | The T-SPOT.TB test is the only TB test with sensitivity and specificity exceeding 95%. The T-SPOT.TB test is reliable even in challenging testing populations, including BCG-vaccinated and immunocompromised persons, and relies on routine phlebotomy procedures.1 |
| How much does the test cost? | Please contact the Customer Experience Team at 01235 433164. We will put you in touch with your local area representative who will offer you a tailored package, according to your needs. |
| What is the sensitivity and the specificity of the T-SPOT.TB test? | The sensitivity of the T-SPOT.TB test is 98.8% and the specificity of the T-SPOT.TB test is 100%.1 |
| Are any patient groups excluded from testing with the T-SPOT.TB test? | No, the T-SPOT.TB test can be used in testing of all patient groups including those living with HIV/AIDS, those with weakened immune systems, recent contacts of TB cases and residents and employees of high risk congregate settings.1 |
| Can the T-SPOT.TB test be used in testing samples from patients with weakened immune systems? | Yes, the T-SPOT.TB test is well suited for use in patients with weakened immune systems.Each sample undergoes a cell count which is used to create a normalized (standardized and known number) suspension of cells that are subsequently incubated with TB specific antigens. Immunocompromised patients may have a reduced number of peripheral blood mononuclear cells (PBMCs) the types of white blood cells used in the T-SPOT.TB test. In these patients, multiple blood tubes can be pooled to obtain the required number of cells to perform the test. Pivotal clinical study data submitted to the US Food and Drug Administration (FDA) for pre market approval extensively evaluated the T-SPOT.TB test in immunocompromised individuals including, but not limited to, subjects with HIV, silicosis, diabetes, end stage renal disease and organ transplant. A negative tuberculin skin test was associated with being immunocompromised; while no association was observed between T-SPOT.TB test result and immunocompromised status.1 |
| Does the T-SPOT.TB test differentiate between latent TB infection and TB disease? | No, like a tuberculin skin test (TST) and the ELISA based TB blood test, the T-SPOT.TB test does not differentiate latent TB infection from TB disease.1 |
| How soon after exposure to Mycobacterium tuberculosis can an infection be detected with the T-SPOT.TB test? | The time interval for conversion following exposure is not yet well defined, but is expected to occur no later than tuberculin skin test (TST) conversion (typically 2 8 weeks).1 |
| Is a positive T SPOT.TB test result expected in patients with a previous history of tuberculosis? | Unfortunately, there is no clear answer to this question. Studies do not consistently demonstrate that persons test negative after TB treatment. Clinical cure is described by negative sputum culture, improvement of symptoms and chest x ray changes. This term refers to both a sterilizing cure and the return to the quiescent phase (latent TB infection). Some data have shown that a large proportion of individuals remain skin or blood test positive. The persistence of effector T cells, the cells stimulated by TB specific antigens in the T SPOT.TB test, may suggest the presence of dormant bacteria but further study is required. Depending on requirements, other diagnostic tests and medical examinations could be considered if the patient remains positive after treatment.2-5 |
| Can the T-SPOT.TB test detect infections of drug resistant tuberculosis strains such as MDR TB, XDR TB or TDR TB? | Yes, the T-SPOT.TB test can detect all strains of Mycobacterium tuberculosis complex organisms, including multi drug resistant tuberculosis (MDR TB), extensively drug resistant tuberculosis (XDR TB) and totally drug resistant tuberculosis (TDR TB). The antigens in the T-SPOT.TB test are common to all Mycobacterium tuberculosis strains. However, the test does not predict whether the organism is sensitive to usual drug treatments. Drug susceptibility testing occurs after isolation and identification of the organism by other methods.1 |
| Are infections with mycobacteria other than Mycobacterium tuberculosis expected to produce positive T SPOT.TB test results? | Mycobacterium tuberculosis is the causative agent of most cases of tuberculosis and thus, T SPOT.TB test sensitivity was determined from subjects with active, culture confirmed Mycobacterium tuberculosis infection. Individuals infected with other Mycobacterium tuberculosis complex organisms (such as M. bovis, M. africanum, M. microti, M. canetti) usually have T cells in their blood which recognize the antigens (ESAT 6 and CFP10) used in the T SPOT.TB test and are also anticipated to produce positive T SPOT.TB test results. ESAT 6 and CFP10 antigens are absent from most non tuberculous mycobacteria (NTM) with the exception of M. marinum, M. szulgai and M. kansasii. While it is unclear if ESAT 6 and CFP10 are present in the genome of all subspecies of M. gordonae, it is possible that this NTM may also produce a positive result. All other non tuberculous mycobacteria, including M. avium, are not expected to cross react with the antigens used in the T SPOT.TB test.1 |
| Is the T SPOT.TB test affected by previous BCG vaccination? | Unlike a tuberculin skin test, there is no association between BCG vaccination and T SPOT.TB test results. The bacille Calmette Guérin (BCG) vaccine is an attenuated derivative of virulent Mycobacterium bovis, the bovine or animal form of the TB mycobacterium. The T SPOT.TB test utilizes antigens (ESAT 6 and CFP10) that are located on a genomic region designated as RD1, region of differentiation 1. The RD1 region is present in all virulent M. bovis strains but is deleted from all BCG strains. Because the antigens used in the T SPOT.TB test are not present in the BCG vaccine, the T SPOT.TB test does not produce a false positive result due to BCG vaccination. It should be noted, however, that patients infected with virulent M. bovis are likely to produce a positive T SPOT.TB result.1 |
Sample collection
| Question | Answer |
|---|---|
| Do blood samples need to be collected in special collection tubes? | No, Oxford Diagnostic Laboratories accepts samples in standard green top tubes (lithium heparin or sodium heparin). Blood samples may also be collected in sodium citrate tubes. |
| Can blood collection tubes containing EDTA (purple top tubes) be used? | No, EDTA (ethylenediaminetetraacetic acid) affects cells’ secretion of interferon gamma due to its chelating (calcium binding) properties. Blood collection tubes that contain this anti coagulant therefore cannot be used. |
| How much blood is needed for the T SPOT.TB test? |
Typically, in immunocompetent patients, sufficient peripheral blood mononuclear cells (PBMCs) to perform the T SPOT.TB test can be obtained with the following age dependent guidelines:1
Please note: The above guidelines may be insufficient in immunocompromised patients with low numbers of PBMCs. Therefore, it may be advisable to collect double the recommended blood volume for immunocompromised patients. |
| What information is required on the blood collection tube? | The tube should be labelled with the patient’s identification as well as the date and time of sample collection. This information must correspond to the information on the accompanying request form. |
| Do you accept other types of specimens beside blood? | No, only whole blood samples collected in lithium heparin, sodium heparin, or sodium citrate tubes are accepted. |
| How should blood samples be stored prior to sending to the laboratory? | Blood samples must be stored at room temperature, between 18 25°C, until packaged for transport and should not be centrifuged or refrigerated. |
| After collecting a blood sample, how long do I have to send it to the laboratory? | Blood samples can be shipped on the same day or overnight, as long as they are received by the laboratory no later than 2.00pm the day following venepuncture. |
| In which circumstances would the laboratory reject a blood sample? |
If a blood sample is rejected, this will be outlined on the report. Additionally, someone may contact you. Examples of reasons why a blood sample would be rejected are listed below:
|
Send samples
| Question | Answer |
|---|---|
| How can I start sending samples to the laboratory? | Getting started is a simple, easy process. Contact the Customer Experience Team on 01235 433164 and we will review the steps with you. |
| When can samples be sent to Oxford Diagnostic Laboratories? | Samples are accepted before 2.00pm Monday through Saturday (excluding public holidays). Please see our service closures for exception. |
| Which requisition form should be used? | The Oxford Diagnostic Laboratories Request Form should be used. This will be provided to you when your account is set up with us. |
| How are samples shipped to the laboratory? | There are at least 3 shipping methods available to customers. If you need help in choosing a method, or would like help with packing materials, please contact the Customer Experience Team on 01235 433164 for assistance. |
| How does DX work? | DX is a courier network usually collecting from you after 5pm and delivering to us by 9am next day (may vary depending on location). There is a one off fee to register and set up a DX box. Once this is complete, simply place the samples into the box before the scheduled pick-up time and a courier will collect the sample(s) and deliver them to Oxford Diagnostic Laboratories. If assistance is needed in setting up a DX account, please contact the Customer Experience Team on 01235 433164. |
| How should samples be packaged? | Ensure blood samples are securely packaged in a robust blood transport container for secure and safe transit (in accordance with IATA Packing Instructions 650). Packaging should also clearly show the UN3373 number. Please contact the Customer Experience Team on 01235 433164 for further details. |
Results interpretation
| Question | Answer |
|---|---|
| When will I get the results? | Assuming overnight shipment, results are usually reported the day following receipt of the sample. If same day samples arrive after test processing start time, they may be carried over until the next day, which means that results will be available one day later. The only exceptions are during public holidays, weekends, the Christmas to New Year period and for high volume screenings. During these times, we endeavour to return results within 3 working days. |
| How will I receive T SPOT.TB test results? | Test results will be communicated to the designated person(s) identified in the New Customer Registration Form. Results are sent via secure email and are also available via our secure Web Portal. Electronic requesting and result reporting is available using the Labgnostic lab-to-lab system. Please discuss your preferred format with our Customer Experience Team on 01235 433164. |
| How are T SPOT.TB test results reported? | T SPOT.TB test results are reported as positive, negative, borderline, or indeterminate. |
| How are T SPOT.TB test results interpreted? | T SPOT.TB test results are qualitative and are reported as positive, borderline (equivocal) or negative, given that the test controls perform as expected. Test results are determined by firstly enumerating the spots (captured interferon gamma from individual T cells) in each of the patient’s four test wells (Positive Control, Nil Control, Panel A, Panel B). Spots can be counted from the test wells using a magnifying glass, stereomicroscope, ELISPOT reader, or a digital image captured from a microscope. Qualitative results are interpreted by subtracting the spot count in the Nil (Negative) Control from the spot count in Panels A and B. Detailed information regarding test result interpretation can be found in the [T SPOT.TB package insert] URL TBD and on your results report.1 |
| Why does the T SPOT.TB test have a borderline for interpretation of results? | The vast majority of T SPOT.TB test results are either positive or negative. A small percentage of test results can be borderline (equivocal), where the higher of (Panel A minus Nil Control) and (Panel B minus Nil Control) is 5, 6 or 7 spots. The borderline category is intended to reduce the likelihood of false positive or false negative results around the cutoff point of the T SPOT.TB test. As opposed to an indeterminate or invalid result, a borderline result is clinically interpretable and should be followed by retesting as a substantial proportion of individuals may test positive upon retesting.1 |
| Are borderline T SPOT.TB test results the same as indeterminate results? | No, borderline (equivocal) results are clinically interpretable whereas indeterminate results cannot be interpreted due to the failure of the test’s Positive and/or Nil (Negative) Control. In both cases, however, retesting by collecting another blood sample is recommended.1 |
| What should I do with a borderline T SPOT.TB test result? | Borderline results are clinically interpretable and should be followed. Retesting by collecting another sample is recommended.1 |
| What should I do with an indeterminate T SPOT.TB test result? | Indeterminate results are not clinically interpretable and may occur if the Positive and/or Nil (Negative) Control does not perform as expected. Retesting by collecting another sample is recommended. Upon retesting, if the test result remains indeterminate, other diagnostic tests and/or epidemiologic information should be used to help determine the TB infection status of the patient. Indeterminate results are uncommon and may be related to factors such as inappropriate blood storage conditions, delay in sample transport, patient specific conditions, or laboratory error.1 |
| What is the expected frequency of indeterminate results with the T SPOT.TB test? | Indeterminate results are infrequent with the T SPOT.TB test.1 Oxford Diagnostic Laboratories maintains a low overall indeterminate rate and does not charge for indeterminate T SPOT.TB test results. |
Featured resources
References
- Oxford Immunotec. T-SPOT.TB Package Insert PI-TB-IVD-UK-v3. Abingdon, UK. 2016.
- Zhang S, Shao L, Mo L, et al. Evaluation of gamma interferon release assays using Mycobacterium tuberculosis antigens for diagnosis of latent and active tuberculosis in Mycobacterium bovis BCG vaccinated populations. Clin Vaccine Immunol. 2010 Dec;17(12):1985 90.
- Bosshard V, Roux Lombard P, Perneger T, et al. Do results of the T SPOT.TB interferon gamma release assay change after treatment of tuberculosis? Respir Med. 2009 Jan;103(1):30 4.
- Chee CB, KhinMar KW, Gan SH, et al. Tuberculosis treatment effect on T cell interferon gamma responses to Mycobacterium tuberculosis specific antigens. Eur Respir J. 2010 Aug;36(2):355 61.
- Walzl G, Ronacher K, Hanekom W, Scriba TJ, Zumla A. Immunological biomarkers of tuberculosis. Nat Rev Immunol 2011; 11: 343 354.
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