The aim of the study is to pilot the application of a novel ESAT6/CFP10 (C-TST) skin test in rheumatologic disease patients prior to initiation of treatment with biologic and/or targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARD). This is a prospective observational study involving the recruitment of patients with rheumatologic diseases who are planned for initiation of b/tsDMARD. Eligible patients would undergo skin testing by the Mantoux technique with purified protein derivative (PPD) RT23 on one forearm and C-TST on the other, alongside routine blood sampling for Interferon-Gamma Release Assay. The skin test results would be read within 48-72 hours afterwards. Treatment of TB infection would be provided in accordance with current clinical guidelines, followed by regular clinical monitoring for 2 years. Analyses involve performance evaluation of C-TST, and decision-analytical modelling incorporating multiple Markov process to evaluate the impact of management by LTBI testing methods on clinical outcomes and health care costs.

Objective. The aim of the study is to pilot the application of a novel ESAT6/CFP10 (C-TST) skin test in rheumatologic disease patients prior to initiation of treatment with biologic and/or targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARD), with the objectives of determining its performance and the cost-effectiveness of clinical management for latent tuberculosis infection (LTBI).

Design. A prospective observational study

Setting. Rheumatology Specialist clinic services in Hong Kong

Methods. This study involves the recruitment of patients with rheumatologic diseases who are planned for initiation of b/tsDMARD. Eligible patients would undergo skin testing by the Mantoux technique with intradermal injection of 2U purified protein derivative (PPD) RT23 on one forearm and 5U of C-TST on the other, alongside routine blood sampling for Interferon-Gamma Release Assay (IGRA) with QuantiFERON-TB Gold. The skin test results would be read within 48-72 hours afterwards. Treatment of LTBI would be provided in accordance with current clinical guidelines, followed by regular clinical monitoring for 2 years. Analyses involve performance evaluation of C-TST, and decision-analytical modelling incorporating multiple Markov process to evaluate the impact of management by LTBI testing methods on clinical outcomes and health care costs.

Main outcome measures. Concordance between different tests for LTBI by Kappa measure; sensitivity and specificity of C-TST test estimated with current standard; proportion of new TB cases averted, discounted QALYG and ICER.

Anticipated outcome. The study would provide preliminary evidence regarding the diagnostic performance of C-TST, and impact of its utilisation for treatment decision for rheumatologic diseases patients in the prevention of active tuberculosis diseases.

Inclusion Criteria:

1. adult of age ≥ 18 and up to 65 years;
2. diagnosis of at least one classified rheumatologic disease; and
3. being planned to receive b/tsDMARDs therapy,
4. can communicate in Chinese and/or English.

Exclusion Criteria:

• diagnosis of active TB diseases,
• currently receiving TB or LTBI treatment;
• concurrent mental illnesses;
• prisoners.

Rheumatology patients followed up at the Specialist Services of regional hospitals in New Territories East Cluster in Hong Kong (Prince of Wales Hospital, Alice Ho Miu Ling Nethersole Hospital and North District Hospital)

Access of individual level data at individual level is restricted for protection of privacy, as stipulated in the institutional approval