Background Patients with rheumatic disorders treated with TNF-α inhibitors have a 3–4 fold increased risk of developing TB. Our local population (Slough, UK) has a very high TB incidence with a rate of 58.5 per 100,000 population in 2012, approximately four times the national average. Latent TB in our population, many of whom are on immunomodulatory treatment, is thus likely to be several-fold higher.
NICE guidance recommends that immunocompromised patients should be screened for latent TB using either an Interferon Gamma Release Assay (IGRA) alone or in combination with a tuberculin skin test.
Two currently available IGRAs are the TB-ELISPOT and QuantiFERON-TB Gold In Tube (QFT) test. The NICE guidelines do not distinguish between these two assays. Whilst they have enhanced our ability to diagnose latent TB their use in immunosuppressed patients has not been widely evaluated. Furthermore, there is limited evidence to support the superiority of either of the two assays.
Objectives We aim to:
Study the effectiveness and outcomes of our current TB screening programme prior to biologic therapy in our high risk immunosuppressed patients
Compare two currently used IGRAs (ELISPOT and QFT) in this population of patients.
Methods Retrospective data was obtained from our patient database. 246 consecutive patients (39% male and 61% female; age range 29 – 86 years; 78.5% Caucasian, 19.5% Asian and 2% other) were identified with inflammatory rheumatic disorders who had undergone clinical screening, a chest radiograph and an IGRA (either one or both of TB ELISPOT or QFT) prior to use of a biologic agent between 2008 and 2015.
Results 16/246 (6.5%) patients had a positive IGRA. Of these 15 received chemoprophylaxis for latent TB. 12 (75%) of these patients were Caucasian and the remainder were Asian. 230/246 (93.5%) patients were IGRA negative. 190 patients were receiving immunosuppressant therapy at the time of screening and 245 patients screened were subsequently treated with TNF inhibitors. In this 7-year period there have been no cases of TB reactivation reported to date.
Of the patients screened with both IGRAs, the majority of patients tested negative for both (158/171, 92.4%). 13/171 (7.6%) patients had a positive result. Of these 6 tested positive for both ELISPOT and QFT, 4 had a positive ELISPOT only, and the remaining 3 had a positive QFT test only. The concordance of the two assays used was thus 95.9% (164/171 patients).
The absence of TB reactivation in our high risk immunosuppressed population receiving biologic therapy indicates the effectiveness of our current screening strategy.
The current study demonstrates good concordance between the ELISPOT and QFT assays, suggesting that the use of either test on its own is sufficient for screening for latent TB in this population. This data supports current NICE guidance on diagnosing latent TB in the immunocompromised population.
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National Institute of Health and Clinical Excellence. Tuberculosis - full guideline [internet]. NICE. 2016. http://www.nice.org.uk/guidance/ng33
Ding T, Ledingham J et al. BSR and BHPR Rheumatoid Arthritis Guidelines on Safety of anti-TNF therapies. Rheumatology. 2010;49:2217–19
Disclosure of Interest None declared