Objectives To determine the rate of tuberculosis (TB) screening test conversion during anti-tumour necrosis factor (TNF) therapy in rheumatic patients with negative baseline screening.

Methods This was a prospective study of rheumatic patients with negative baseline TB screening (tuberculin skin test (TST): <5 mm, and negative T-SPOT.TB, QuantiFERON-TB Gold In Tube (QFT-GIT) and chest X-ray) treated with anti-TNF agents. All patients underwent re-screening for TB with all assays 1 year later. Factors associated with TB test conversion were analysed and compared between ‘converters’ and ‘non-converters’.

Results Seventy patients (mean age 50.6±15.5 years) with rheumatic disease (33 with rheumatoid arthritis, 33 with spondyloarthropathies and 4 with other conditions) were enrolled. Patients were treated with different anti-TNFs (27 with adalimumab, 14 etanercept, 16 infliximab, 8 golimumab, 5 certolizumab pegol) for 1 year. Twenty patients (29%) displayed conversion of at least one screening assay 12 months after anti-TNF therapy: conversion of TST occurred in 9 (13%), T-SPOT.TB in 7 (10%) and QFT-GIT in 5 (7%). Only one patient had concomitant conversion of more than one screening test. Univariate and multivariate analysis revealed that only infliximab was associated with a decreased rate of TB screening assay conversion (OR 0.048, 95% CI 0.004 to 0.606, p=0.017). No patient (40% received isoniazid therapy) developed active TB during follow-up (27±12 months).

Conclusions Approximately one third of patients with negative baseline TB screening develop conversion of at least one screening test during anti-TNF treatment. These findings should be considered when designing re-screening strategies and contemplating latent TB therapy.