IGRAtests

IGRATests refer to interferon-gamma release assays (IGRAs), a class of blood tests used to detect infection with Mycobacterium tuberculosis by measuring the immune system’s release of interferon-gamma in response to TB-specific antigens. The tests aim to identify latent tuberculosis infection and are used in settings where symptoms of active TB are not present but previous exposure is suspected.

The most widely used formats are the QuantiFERON-TB Gold (including newer generations) and the T-SPOT.TB assay. These tests employ antigens such as ESAT-6, CFP-10, and TB7.7, which are largely absent from Bacille Calmette-Guérin (BCG) vaccines and most non-tuberculous mycobacteria, reducing cross-reactivity and yielding fewer false positives related to prior vaccination.

IGRATests are commonly used as an alternative to the tuberculin skin test, particularly when BCG vaccination is common or when a patient cannot return for a skin-test reading. They require a blood draw and laboratory processing, with results typically available within a day or two depending on the assay and workflow.

Limitations include that a positive IGRA indicates TB infection but does not distinguish latent infection from active disease. A negative result does not completely exclude infection, especially in immunocompromised individuals or very early infection. Indeterminate results can occur due to technical or immune-related factors. Costs and the need for laboratory infrastructure are considerations in their use.

In clinical practice, IGRATests are used alongside clinical evaluation, chest radiography, and microbiological testing to assess TB infection status. They are not diagnostic of active TB on their own.