P42 Are chest X-rays still necessary for prebiologic tuberculosis screening? A retrospective audit

Abstract

Abstract Biologics are commonly used in autoimmune dermatological conditions as an option if other treatments are unsuccessful or contraindicated. However, one major side-effect of biologics is immunosuppression, which may lead to the reactivation of latent tuberculosis (TB) in patients. The British Association of Dermatology has implemented guidelines that require doctors to screen for TB before prescribing biologics to patients. The 2020 guidelines advise screening questions, performance of a chest X-ray (CXR) and an interferon-γ release assay (IGRA). Current studies show that CXR has a sensitivity of 15% when diagnosing latent TB. While there is no gold standard for diagnosing latent TB, the IGRA is a commonly used test and is shown to be four times more effective than the tuberculin skin test. This study questions the diagnostic value of CXR in the screening of TB in asymptomatic patients, and whether it should be removed from the guidelines for such patients. A retrospective audit of dermatological patients in our trust was done over a 24-month period (January 2020–January 2022). Patients selected for the audit were those diagnosed with psoriasis or hidradenitis suppurativa and started on biologics during this 24-month period. Patients were assessed on the following: patient history, CXR results, IGRA results and screening outcomes. The data were quantitatively analysed to uncover the necessity of performing a CXR on patients starting biologics. Between January 2020 and January 2022, 77 patients were scheduled for prebiologic TB screening; CXRs were performed in 74 patients (96%), while 72 (94%) of patients had IGRA tests. During this period, three patients (4%) were diagnosed with latent TB based on positive IGRA results and normal CXR findings. They were subsequently treated for latent TB infection prior to biologic therapy. None of the patients with negative IGRA results had positive CXR findings for TB. This finding suggests that CXR is unnecessary at the initial stage of prebiologic TB screening for asymptomatic patients. IGRA can detect both latent and active TB, while CXR is recommended for the diagnosis of active TB. Mandating CXR comes at a cost to the National Health Service and subjects patients to unnecessary radiation exposure. We propose that CXR be done only for patients who are either symptomatic for TB or have a positive IGRA result.