An IGRA (interferon gamma release assay) is a blood test which, like the tuberculin skin test (THT), detects a tuberculosis infection (LTBI). It is carried out by the public health department or doctor's surgery if an infection is suspected. Two different IGRA test systems, the ^{QuantiFERON®} test and the ^ELISpot®, are commercially available. One advantage of the IGRA tests over the tuberculin skin test is that the result is not influenced by a previous BCG vaccination or non-tuberculous mycobacteria. In addition, no second appointment is necessary for reading, the test is carried out from a blood sample.

A positive IGRA test indicates that the person either has a latent tuberculosis infection or has been in contact with the tuberculosis bacteria in the past. However, a positive test does not indicate whether the person has the disease. An X-ray examination of the lungs and, if necessary, further examinations must be carried out to rule out a disease. Once a diagnosis of latent tuberculosis infection (LTBI) has been made, preventive treatment should be given. This can significantly reduce the risk of contracting the disease.

After tuberculosis has taken place, the IGRA tests usually remain positive and can no longer be used in the diagnosis of LTBI.