Diagnostic Biomarkers for Uveitis: Serum BAFF and CXCL9 in Differentiating Ocular Sarcoidosis, Tuberculosis and Other Entities with Implication for QuantiFERON-Positive Uveitis

To evaluate serum B cell activating factor (BAFF) and CXCL9 as diagnostic biomarkers for ocular sarcoidosis and ocular tuberculosis (TB). We also explore their role in the stratification of patients with QuantiFERON (QFT)-positive uveitis without another identifiable cause. Eighty uveitis patients with various entities were included: 10 with ocular sarcoidosis, 35 with TB-related uveitis (including 11 confirmed (ocular TB) and 24 QFT-positive uveitis of unknown cause) and 35 with other uveitis entities. Levels of serum BAFF and CXCL9 were measured. Serum BAFF was higher in ocular sarcoidosis compared to other groups (area under the curve (AUC) = 0.74; 95% CI: 0.53–0.96, <i>p</i> = 0.017). At an optimal serum BAFF cut-off point of 772.3 pg/ml, the sensitivity was 70.0% (95% CI: 39.7–89.2) and the specificity was 89.1% (95% CI: 77.0–95.3). Serum CXCL9 was comparable between ocular sarcoidosis and confirmed ocular TB but was significantly higher in these groups compared to other uveitis entities (AUC = 0.71, 95% CI: 0.57–0.86, <i>p</i> = 0.011). To differentiate ocular sarcoidosis and TB from other uveitis entities, CXCL9 (cutoff: 105.5 pg/ml) showed a sensitivity of 88.9% (95% CI: 67.2–98.0) and a specificity of 54.3% (95% CI: 38.2–69.5). High CXCL9 TB-related uveitis patients demonstrated a higher proportion of uveitis resolution when fully treated with antitubercular treatment (ATT) (<i>p</i> = 0.027). Serum BAFF and CXCL9 serve as potential diagnostic biomarkers for differentiating ocular sarcoidosis, ocular TB and other uveitis entities. These might identify QFT-positive uveitis who are most in need of ATT.