Background Screeing latent TB before biologic or immunosuppression thearpy is important in high incidence of tuberculosis population.

Objectives Objective:To investigate the roles of tuberculin skin test and interferon-gamma stimulation test in the diagnosis of latent tuberculosis infection in patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and ankyolosing spondylitis (AS).

Methods Methods: The study enrolled 329 consecutive patients, 62 with SLE, 179 with RA, and 88 patients with seronegative spondyloarthropathy (SSA; 82 with AS and 6 with undifferentiated spondyloarthropathy). Tuberculin skin test (TST) was performed by Tuberculin PPD RT23 SSI 2 TU/0.1ml. Interferon-γ assay was performed by QuantiFERON-TB Gold (QFT). Receiver operating characteristic (ROC) curve analysis was used to determine the optimal cut-off point for latent TB on the PPD test.

Results Results: A positive QFT-G result was observed in 17.9% RA, 15.9% SSA, and 11.3% patients with SLE. There was no statistically significant association between QFT-G result and sex, disease duration, prednisone use, or use of disease-modifying antirheumatic drugs. Men had a multivariate-adjusted OR of 2.53 (95% CI, 1.3-4.92) for a positive PPD result (if defined as an induration ≥10 mm). In RA patients, QFT was found best differentiated with PPD≧ 10.5 mm. Among RA patients, the optimal PPD cut-offs for women, men, prednisone users, and prednisone nonusers were ≥10.5 mm, ≥10 mm, ≥10.5 mm, and ≥10.5 mm, respectively. SSA patients were best differentiated with a PPD induration ≥16.5 mm; however, the optimal cut-off for SLE patients was a PPD induration ≥9 mm.

Conclusions Conclusions: TST in LTB screening remains useful due to its low cost. In patients who will receive biologic therapy an induration of PPD 5mm as positive cute-off for TST needs to be reconsidered. For RA patients PPD≥10 mm, SSA patients ≥16.5 mm in our BCG vaccinated and intermediate tuberculosis burden population maybe appropriate. For those who had anergic TST result should have IGRA test performed, this would cut down on cost and avoidance of unnecessary prophylaxis of latent TB therapy.

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Disclosure of Interest None Declared