Tuberculin Skin Test for the Screening of Latent Tuberculosis Infection Before Starting Treatment with Tumour Necrosis Factor- α Inhibitors In Systemic Immunoinflammatory Rheumatic Diseases in India - A High Burden Tuberculosis Region of the World

Abstract

Aim: India is a high burden tuberculosis country. Past BCG vaccination could cause sensitisation against TB antigens. Patients with systemic inflammatory rheumatic diseases (SIRDs) have inherent anergy . Also, they are often treated with glucocorticoids and other immunomodulatory drugs. These two confounders may affect TST, which is otherwise a robust screening method for studying TB epidemiology. Possibly for these reasons Indian Rheumatology Association did not recommend TST for the screening of TB infection (latent or disease) before initiating TNFi treatment. The present work examined TST results in SIRDs with the objective of whether it could be used for the screening of latent TB infection among SIRD patients in the Indian context. Method: 60 adult rheumatoid arthritis (RA) and 191 axial Spondyloarthritis (axSpA) patients were Mantoux tested using a higher PPD strength of 10 TU to offset inherent disease anergy. The test was read after 48 to 72 hours. It was interpreted according to the nationally recommended cutoffs that takes into account sensitisation to BCG or environmental mycobacteria. Thus, in this study, an induration of >10 mm was considered as ‘latent TB infection’. Results: The positivity among RA and axSpA patients was 31.66% and 40.31% respectively, similar to that seen in adult Indians. Conclusion: Based upon these results use of modified TST with 10 TUPPD using >10 mm induration as the cut-off point is recommended for diagnosing TB infection; the test may be appropriate for the screening of latent TB infection in the Indian setting. IRA may consider revising its policy for latent TB screening accordingly.