Background There are limited data regarding the value of tuberculosis (TB) rescreening in rheumatic patients on biologic (bDMARD) therapies who had a negative baseline TB screening.

Objectives To examine the rates of conversion and reverse conversion at repeated TB screening testing with 2 available assays (tuberculin skin testing-TST and an interferon gamma release assay-IGRA: T-SPOT.TB) in rheumatic patients with negative baseline screening during long term bDMARD treatment.

Methods Rheumatic patients with negative baseline screening (TST and T-SPOT.TB) were re-screened one year after TNF inhibitor (TNFi) therapy (1st rescreening) and ∼6 years later on bDMARDs (2nd re-screening). The rate of conversion and reverse conversions of the 2 assays were recorded. Only patients who did not receive isoniazid (INH) therapy between the 1st and 2nd rescreening were analyzed.

Results Among 70 patients with negative TB baseline screening, 21 patients with 2 re-screenings available were identified; one patient with TST conversion at the 1st rescreening who converted back to negative at the 2nd rescreening after INH treatment, was excluded from the study. 20 patients were finally included in the study (RA=7, PsA=6, AS=5, other diseases=2). 50% were women with a mean age of 57.1±12.4 years and mean disease duration at the last screening of 13.1±6.2 years. The mean interval between the 1st and 2nd rescreening was 68.6±13 months. At the last evaluation, 90% (18/20) were still on bDMARDs (TNFi=55%, non-TNFi=45%), 45% (9/20) on non-biologic DMARDs and only one patient (5%) on corticosteroids. None of the patients displayed conversion or reverse conversion with T-SPOT.TB compared to 6 (30%) with TST at the 2 rescreenings (p=0.02). At the 1st rescreening, 4/20 (25%) had converted their TST to positive; at the 2nd rescreening, 2 reverted back to negative (1 patient with PsA on etanercept and 1 with RA on steroids, methotrexate and golimumab) while the other 2 remained TST positive (1 with PsA on etanercept and 1 with Still's disease exposed to etanercept, tocilizumab and canakinumab). Among the 16 patients who remained TST and T-SPOT.TB negative at the 1st rescreening, 2 (12.5%) became TST positive at the 2nd rescreening (12 mm and 7 mm, respectively). Both patients were on long term infliximab treatment without history of TB exposure. After thorough evaluation, no evidence of active TB infection was found in any of the 6 patients who converted TST either in the 1st or 2nd rescreening.

Conclusions Among rheumatic patients with negative baseline TB screening, conversion or reverse conversions were much more frequent with TST compared to an IGRA (T-SPOT.TB) at repeat testings during long term bDMARD therapy. These preliminary findings need to be taken into account while designing the appropriate repeat TB screening strategy for this group of patients.

Acknowledgements Supported by research grants from the Special Account for Research Grants (S.A.R.G.), National and Kapodistrian University of Athens, Athens, Greece.

Disclosure of Interest None declared