C4A and systemic lupus erythematosus: In the context of distinguishing ANA+ SLE vs. OD (Figure 2B), TC4d (AUC:0.84) significantly outperformed EC4d (0.71, p = 0.01), anti-Smith (0.66, p <0.01), C3 (0.64, p <0.01), C4 (0.64, p < 0.01) but not anti-dsDNA (0.76, p = 0.06) or BC4d (0.85, p = 0.89).