Retrospective study of interferon gamma release assays (IGRAs) done in a district general hospital (DGH) for the screening of patients prior to biological therapies

Abstract

Background: The British Thoracic Society (BTS) produced guidelines in 2005 for the assessment for and treatment of latent and active tuberculosis (TB) prior to anti tumour necrosis factor (TNF) therapy. Interferon gamma release assays (IGRAs) are not included in these. These patients are often immunosuppressed, therefore tuberculin skin testing (TST) alone is not reliable to rule out latent TB. Aim: To assess whether there is an increasing demand for IGRAs done prior to anti-TNF and whether TST is also being used appropriately. Method: We collected data on IGRAs done in the hospital since their introduction in 2011 until 31/12/2014. Data was recorded for: the result of the test; TST prior to IGRA and result; whether the patient was immunosuppressed; the result of the IGRA and the outcome. Results: 260 tests were done, 13 were excluded due to insufficient data. 24 were done pre biological therapy: 1 in 2011, 2 in 2012, 5 in 2013 and 16 in 2014. All 4 patients with a positive IGRA were given chemoprophylaxis. None of the patients who had a positive TST and negative IGRA were given chemoprophylaxis. Conclusion: IGRA testing is increasingly being used to screen patients for TB prior to commencing anti-TNF. The use of TST prior to IGRA is variable and results for the tests do not always correlate. Guidelines for screening these patients need updating to incorporate IGRAs and advise on the use of TSTs.