C3 and systemic lupus erythematosus: Three recent studies found that urinary BAFF can discriminate LN from non-renal SLE with an AUC of 0.79–0.93 [112,122], with a low Sn of 20% and a high Sp of 91% [123], outperforming the conventional markers analyzed concomitantly (AUC 0.45–0.66 for anti-dsDNA, 0.57–0.81 for serum C3, and 0.61–0.63 for serum C4) [112,122].