Tuberculosis test IGRA – blood test for screening for tuberculosis
The tuberculosis test IGRA is a venous blood test for screening for tuberculosis infection. The analysis is primarily intended for people who need to perform a tuberculosis screening and be able to share their test results with, for example, employers, educational providers, internships, authorities or other third parties.
IGRA stands for "Interferon Gamma Release Assay" and is an immunological analysis that examines whether the immune system reacts to specific antigens from bacteria within the Mycobacterium tuberculosis complex. The analysis is particularly useful for identifying an immunological response that may be consistent with previous or latent tuberculosis infection.
Screening for tuberculosis infection
The test is aimed at people without suspicion of ongoing active tuberculosis disease. It may, for example, be relevant when a tuberculosis result is requested prior to work, studies, internships, stays abroad or other situations where screening is required. Karolinska states that the IGRA analysis is primarily used for screening or infection tracking of latent tuberculosis. If active tuberculosis is suspected, other targeted diagnostics are recommended instead.
How the IGRA analysis works
The IGRA test does not look for the tuberculosis bacterium itself in the blood. Instead, the test measures how the immune system reacts to specific substances from the tuberculosis bacterium. If the body has previously been in contact with tuberculosis, certain T cells can react and release interferon-gamma, IFN-γ. The amount of interferon-gamma is then measured in the laboratory and used together with the test's control values to assess the result.
Three results are included in the test result
The IGRA analysis includes Tuberculosis Ag 1 and Tuberculosis Ag 2, which are analyzed together. The quantitative IFN-gamma responses are reported separately in IU/mL and the laboratory also provides a summary interpretation of the entire analysis.
- Tuberculosis-Ag, IFN-gamma response Interpretation
- Tuberculosis-Ag 1, IFN-gamma response
- Tuberculosis-Ag 2, IFN-gamma response
The summary interpretation is reported as positive, negative or not assessable.
What does a positive IGRA result mean?
A positive IGRA result means that the immune system has shown a reaction to the tuberculosis-specific antigens used in the analysis. The result may indicate tuberculosis infection, but the test cannot determine whether it is latent tuberculosis infection or active tuberculosis disease. Latent tuberculosis means that a person has an immunological response after tuberculosis infection but does not have active tuberculosis disease. Latent tuberculosis is not contagious. A positive IGRA result therefore needs to be followed up with a medical assessment to determine whether further investigation is appropriate.
A positive IGRA result requires a medical assessment and may be subject to infection control notification
If your IGRA test is positive, the result needs to be followed up and assessed by a doctor. A positive IGRA result shows that the immune system has reacted to tuberculosis-specific antigens, but the test cannot determine whether it is a latent tuberculosis infection or active tuberculosis disease. Further medical investigation may therefore be needed to exclude or confirm active tuberculosis, after which you will be contacted by a doctor for further investigation.
Tuberculosis is a notifiable, public health hazard and infection-tracing disease according to Swedish infectious disease legislation. If the medical follow-up leads to suspicion of or confirmed tuberculosis disease, a report is sent to the regional infectious disease physician and the Public Health Agency in accordance with the applicable infectious disease regulations.
This means that a positive screening result is not only given without medical follow-up. You will need to consult a doctor for assessment of the result and a position on any further investigation and infection control management.
The test should not be used if active tuberculosis is suspected
Note!The test is intended for screening and should not be used if there are symptoms or suspicion of active tuberculosis disease. If you experience symptoms such as prolonged cough, fever, night sweats, unexplained weight loss or other symptoms that may raise suspicion of active tuberculosis, you should instead seek medical attention for medical assessment and targeted diagnostics.
Sampling is only performed at specific Karolinska units
The sample is taken as a venous blood sample and requires special sample handling. Tuberculosis Ag IGRA can therefore only be performed at selected sampling units within the Karolinska University Laboratory that offer IGRA sampling.
Always check the current sampling unit and what times IGRA sampling is offered before your visit. See Karolinska's current list of units that perform IGRA testing.
