Diagnostic accuracy of T-SPOT.TB and TST in detecting active tuberculosis in patients with rheumatic immune diseases: a fully matched comparative study

Background and objectives Patients with rheumatic immune diseases (RD) are considered a high-risk population for developing active tuberculosis (ATB). Timely and accurate diagnosis of ATB in RD patients is critical for optimizing treatment outcomes and improving prognosis. Both interferon-gamma release assays (IGRA) and the tuberculin skin test (TST) are immunological methods employed in the diagnosis of tuberculosis. However, the diagnostic accuracy of these tests in RD patients, who often experience immune dysfunction, remains underexplored. This study aims to compare the diagnostic accuracy of TST and T-SPOT.TB in RD patients with suspected tuberculosis symptoms. Methods This prospective study included RD patients presenting with any of the following symptoms-fever, cough, night sweats, or unexplained weight loss (all symptoms recommended by the World Health Organization for tuberculosis screening)-from September 2014 to September 2015. Both T-SPOT.TB and TST were performed, and patients were categorized into ATB and non-ATB groups based on clinical diagnosis (including microbiologically confirmed and clinically diagnosed cases). Receiver operating characteristic (ROC) curves were constructed to compare the diagnostic accuracy of T-SPOT.TB and TST for ATB and to determine the optimal cutoff values. Sensitivity, specificity, predictive values, and likelihood ratios were calculated, along with 95% confidence intervals (CIs). The concordance between T-SPOT.TB and TST in diagnosing ATB was also evaluated. Results A total of 300 RD patients were enrolled in the study. Of these, 35 (11.7%) were diagnosed with ATB, 258 (86.0%) were excluded from ATB, and 7 (2.3%) had an unclear diagnosis. Among the RD patients, the ATB group exhibited significantly higher frequencies of night sweats (34.3% vs. 14.0%, p=0.002) and unexplained weight loss (17.1% vs. 3.1%, p Conclusion In RD patients with suspected ATB symptoms, both T-SPOT.TB and TST offer valuable diagnostic assistance. T-SPOT.TB demonstrates superior diagnostic accuracy, particularly in terms of sensitivity. Higher spot counts on T-SPOT.TB or larger induration diameters on TST should raise clinical suspicion for the presence of concurrent ATB.