IL34 and synovitis: Based on the ROC curve, the optimal cutoff value of plasma IL-34 as a non-invasive marker for distinguishing knee OA patients with synovitis from those without synovitis was projected to be 3,060 pg/mL, which yielded a sensitivity of 87.1%, a specificity of 100.0%, and an AUC of 0.94 (95% CI: 0.87 to 1.00; P = 0.001) (Fig. 5I).