Comparison of PPD and IGST Sensitivity in Latent Tuberculosis Assessment (Cross-sectional Study)

Objective: Purified Protein Derivative (PPD) and Interferon Gamma Release Assay (IGRA) were performed on patients with ankylosing spondylitis and rheumatoid arthritis who were planned to initiate immunosuppressive treatment. The aim was to determine which test would be more appropriate for diagnosing latent tuberculosis (TB) and to evaluate the sensitivity and specificity of PPD and IGRA tests in latent TB diagnosis. Materials and Methods: Forty-seven patients with rheumatoid arthritis and 27 patients with ankylosing spondylitis were included in the study. All patients underwent both PPD and QuantiFERON-TB Gold Plus testing. Latent TB was defined as close contact with active tuberculosis infection and/or presence of suspicious fibrotic/calcified lesions on chest radiography without active tuberculosis infection. Results: The QuantiFERON-TB Gold Plus test demonstrated a specificity of 96.6% and sensitivity of 73.3%, while the tuberculin skin test (TST) showed a specificity of 25.4% and sensitivity of 93.3%. A significant correlation was found between the QuantiFERON-TB Gold Plus test and latent tuberculosis criteria (p<0.001, r=0.562), whereas no statistically significant correlation existed between TST and latent tuberculosis criteria (p=0.309, r=0.120). Conclusion: The IGRA test demonstrated higher specificity and sensitivity compared to TST. Given the lower specificity of TST observed in our study compared to other studies, the IGRA test may be recommended for patients planned to receive prophylactic treatment.