False positives occur after BCG immunization. Some data suggest that combining IGRAs and tuberculin testing improves sensitivity [1,24]. We do not recommend the routine

use of TSTs. [CII] HIV-infected individuals with latent TB infection are much more likely to progress to learn more active TB than HIV-uninfected people [25]. Detection and treatment of latent TB infection are therefore important. Blood tests are available that measure interferon-γ release from T cells after stimulation with antigens largely specific to M. tuberculosis [such as early secreted antigen target (ESAT-6) and culture filtrate protein (CFP-10)] [26]. The current commercially available tests are T-Spot.TB (Oxford Immunotec, Abingdon, Oxfordshire, UK) [which uses enzyme-linked immunosorbent spot (ELISPOT) technology to detect the antigen-specific T cells] and QuantiFERON® Gold In-Tube (Cellestis International Pty Ltd., Chadstone, Victoria, Australia)

(an enzyme-linked immunosorbent assay). Both tests are approved for the diagnosis of latent TB infection in HIV-negative individuals. There are some differences between the two tests, although in general they are unaffected by previous BCG and/or infection with most other mycobacteria (an important exception in the United Kingdom being Mycobacterium kansasii). They are not licensed for the diagnosis of active TB, though the tests may be positive here too (as they detect the host immune response to mycobacterial infection). Limited data

exist regarding their performance in HIV infection, but studies suggest that interferon-γ assays are more specific than TSTs, especially PD0332991 in BCG-vaccinated subjects [27–31]. This is an area of ongoing research. They also appear to retain sensitivity more reliably at lower CD4 cell counts, although the lower threshold has not yet been defined [32,33]. Their advantages also include being a single blood test FAD with no need for patient recall to ‘read’ the result and no requirement for cold-chain storage. However, the blood samples need processing within a limited time, and ‘indeterminate’ (i.e. uninterpretable) IGRA results are more common in HIV-infected subjects. They are also more costly than tuberculin tests, although this may be offset by the savings in, for instance, healthcare worker time [34]. The T-spot TB test may have an advantage over the QuantiFERON® Gold In-Tube test as the number of lymphocytes used in the test is standardized. This is a rapidly developing area but, based on current data, we suggest that IGRAs rather than TSTs are used when screening HIV-positive individuals for latent TB infection. [BIII] Where a patient is considered to have active TB, IGRA tests should not be used as the means by which the diagnosis is confirmed or refuted. If a test is performed, the result must be interpreted in light of the clinical picture, microbiological data and an understanding of the assay’s limitations in this population.