P223 Interferon-gamma release assays used in the diagnostic work-up for active tuberculosis

<h3>Background</h3> Tuberculosis (TB) is a common infection worldwide, existing on a spectrum between latent infection and active disease. Screening and treating people at-risk of TB reduces the incidence of developing active TB in the future and is an important part of England’s national TB strategy. Interferon-gamma release assays (IGRA) are blood tests used to identify people with TB infection. IGRA tests cannot discriminate between latent and active TB. Furthermore, false negatives can occur in active TB leading to delays in diagnosis. <h3>Aims</h3> We reviewed all IGRA tests performed between 1 April 2022 and 31 March 2023 at North Middlesex University Hospital to determine how many were performed to screen for TB infection and identify whether tests were being requested inappropriately. <h3>Methods</h3> A total of 2233 tests from 1424 different patients were identified. Tests requested by teams known to screen regularly for TB infection including occupational health, specialist rheumatology and inflammatory bowel nursing teams and the TB nursing team were assumed to follow guidelines. The remaining 570 tests were individually analysed. All tests that did not yield a result were excluded leaving a total of 134 tests. <h3>Results</h3> We examined the rationale for sending an IGRA in 134 cases. A total of 73 (55%) were requested for suspected active TB. Of these, 10 were positive, 15 indeterminate and 73 negative. One person with an indeterminate test and three with positive tests were treated for active TB. Nobody with a negative IGRA test was diagnosed with active TB. Of the 61 people screened for latent TB ,15 patients received multiple IGRA tests. <h3>Conclusion</h3> We found multiple teams within our hospital ordered IGRA tests to exclude a diagnosis of active TB. Aside from the financial cost of these tests (£2,555), all positive results required additional action (either investigations and/or a review) and potential patient anxiety. Clearer guidance is required on the appropriateness of using an IGRA as part of the diagnostic toolkit for active TB. During our review we noted people screened for latent TB prior to biologics were tested repeatedly. Evidence is lacking on the frequency of screening required in this setting.