QuantiFERON-TB Gold Plus (QFT-Plus test)

Improved version of the interferon gamma release assay (IGRA) for diagnosis of infection with tuberculosis bacteria

The test uses the same proven test principle and procedures as the familiar QuantiFERON-TB Gold Test, but is now optimised with an innovative combination of tuberculosis-specific antigens that elicit immune responses both from cytotoxic CD8+ T cells and CD4+ T helper cells. The new QFT-Plus test uses two different TB antigen vials: the TB1 vial contains peptides that are designed to elicit a cell-mediated immune response from CD4+ helper cells, while the TB2 vial is intended to induce cell-mediated immune responses from cytotoxic CD8+ cells. CD8+ T cells that produce IFN-gamma have been detected in patients with active TB and coinfection with HIV, as well as in children infected with TB.

The test principle:

The diagnostic principle of the Interferon Gamma Release Assay (IGRA) is based on the activation of the immunological memory of T lymphocytes within the individual being tested. Specific antigens of the Mycobacterium tuberculosis complex are used to bring about an in vitro stimulation of T lymphocytes in the heparinised whole blood of the patient. If contact had already taken place between the T cells and these tuberculosis-specific antigens, an increase in interferon gamma secretion shall occur. Detection of an increased INF gamma secretion is then considered as indicative of a latent or active tuberculosis infection.

PLEASE NOTE:

The test, i.e. the positive, quantified value detected, does not permit a distinction between latent or active TB. Additional microbiological testing (sputum microbiology, culture, PCR) and imaging procedures are necessary for further clarification. Nonetheless, a negative IGRA can exclude an active TB with a high degree of probability.

QuantiFERON-TB Gold Plus has the following characteristics:

  • Very high sensitivity of > 95 %
  • Highest specificity of any test for TB infection
  • No cross-reaction with BCG strains, meaning that BCG-vaccinated persons are negative
  • Innovative CD8+ T cell technology
  • Robust and reliable findings

Indication:

  • Targeted testing following risk contact with an index case (e.g. open tuberculosis) approx. 6 to 8 weeks after contact or possibly immediately after contact to obtain an initial value
  • Exclusion of latent tuberculosis before administration of immunosuppressive therapy (especially before administration of a TNF alpha inhibitor)
  • Testing as part of the compulsory standard medical precautions at the workplace
  • Screening of risk patients (e.g. persons travelling from risk countries)
  • Staff screening in the healthcare sector

Material and quantity:

At least 7 ml of lithium heparin blood

Storage and transport:

  • Samples can be submitted from Monday to Friday between 8:00 am and 6:00 pm.
  • Sample transport and storage at room temperature;
  • Always declare samples as CITO samples;
  • The vial must be sent to the laboratory the same day, as the window of time between blood sampling and testing must be < 16 hours;
  • Always note the sampling time on the submission slip.


Please note: In case of suspected infection, the service is charged to the laboratory budget with the exemption code 32006.

Sources:
Robert Koch Institute, Tuberculosis Guide
German Respiratory Society (DGP) / German Central Committee against Tuberculosis (DZK)
and
www.quantiferon.com