Background Rheumatoid Arthritis (RA) patients are at increased risk of having Latent TB infection (LTBI), even 4 times higher, compared to the general population¹. This risk of reactivation dramatically increases with the use of biologic response modifiers (BRMs). Current guidelines strongly recommend LTBI screening and treatment prior to BRM use. Interferon Gamma Release Assays (IGRAs), such as the Quantiferon-TB Gold test (QFT-G) and Enzyme-linked immunospot assay for TB (ELISPOT-TB), have recently been introduced in clinical practice. There is still a limited amount of data on their comparative efficacy in RA, further complicated by the lack of a gold standard.

Objectives To determine a safe and effective strategy for LTBI screening in RA patients.

Methods A retrospective, chart review, study was conducted in RA patients followed at the rheumatology outpatient clinic of an urban hospital, serving an inner city, largely immigrant population. 137 RA patients, who had both TST and QFT-G testing performed during their initial evaluation, were included. QFT-G could be interpreted as positive, negative or indeterminate. All TST testing was performed and interpreted and defined as positive if ≥5mm induration was present. Patients were diagnosed with LTBI if TST and/or QFT-G were positive and were treated with 9 months of Isoniazid/B6 after active TB was ruled out by chest radiography. Additional LTBI screening tests, performed yearly, were recorded for a mean period of 2.54 (sd–1.35) years following the initial negative screen.

Results Out of 137 patients studied, 104 (76%) were classified as Hispanic, reflecting the hospital service population demographics. 4 patients had indeterminate QFT-G and negative TST and were excluded from our analysis. 50 (38%) patients were diagnosed with LTBI with either a positive TST 42 (32%) and/or QFT-G 23 (17%). 15 (11%) were positive and 83 (62%) were negative for both tests. The agreement between TST and QFT-G was 73% (Kappa 0.306, CI-95% 0.136–0.477, p-0.087). A Kappa value of 0.306 represents a low moderate agreement between the two tests. In 83 “double negatives” (both TST and QFT-G were negative), 21 did not have subsequent screening and, of the remaining 62, there were only 3 QFT-G sero-conversions and no TST conversions. None of the patients developed active TB.

Conclusions There was low moderate agreement between TST and QFT-G in our high risk RA population. In the absence of clearly defined gold standard and limitations associated with both tests, we propose early screening with both tests for patients who are immediately going to be started on BRM treatment. Patients who are not immediate candidates for BRM treatment may be safely, and cost effectively, screened with a two step process: initial screening with TST and if negative, IGRA testing. Patients positive for either test should be treated. Subsequent double negatives can be screened yearly for LTBI infection by either TST or QFT-G.

1. Carmona, L., et al., Increased risk of tuberculosis in patients with rheumatoid arthritis. J Rheumatol, 2003; 30(7): p. 1436-9.

Disclosure of Interest None Declared