Diagnostic value of the interferon-γ release assay for tuberculosis infection in patients with Behcet's disease

Background: To investigate the diagnostic value of the interferon-gamma release assay (IGRA) for detecting tuberculosis (TB) infection in patients with Behcet's disease (BD). Methods: We retrospective analyzed the data collected from 173 BD patients hospitalized between 2010 and 2015. Ninety-nine healthy volunteers were enrolled as a control group. IGRA was performed using T-SPOT.TB. The diagnosis of active TB (ATB) was based on clinical, radiological, microbiological, histopathological information and the response to anti-TB therapy. Latent TB (LTB) infection was defined as asymptomatic patients with positive T-SPOT.TB. Results: TB infection was documented in 59 BD patients (34.1%). The sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio and negative likelihood ratio of T-SPOT.TB for the diagnosis of ATB were 88.9%, 74.8%, 29.1%, 98.3%, 3.53 and 0.15, respectively. The receiver-operating-characteristic curve demonstrated that spot-forming cells (SFCs) of 70/10(6) PBMC was the optimal cutoff for diagnosing ATB, with an area under the curve of 0.891. Furthermore, the median SFCs in ATB group was significantly higher than those in LTB infection (466/10(6) PBMC vs. 68/10(6) PBMC, p=0.007) or previous TB infection (466/10(6) PBMC vs. 96/10(6) PBMC, p=0.018). A significant discrepancy between T-SPOT.TB and tuberculin skin test was noted (kappa coefficient=0.391, p=0.002). Conclusions: T-SPOT.TB, an IGRA, may assist in the diagnosis of ATB in BD patients, and the higher SFCs suggest ATB in BD patients.