In the differentiation of SLE vs. AHV (Figure 2C), TC4d (AUC: 0.84) significantly outperformed anti-Smith (0.65, p < 0.01), C4 (0.61, p < 0.01) and C3 (0.58, p < 0.01) but not EC4d (0.84, p = 0.98), BC4d (0.88, p = 0.24) or anti-dsDNA (0.79, p = 0.19). Here, C4A is linked to systemic lupus erythematosus.