C4A and systemic lupus erythematosus: Figure 2A compares biomarker performances in ANA-positive (ANA+ by either method at the time of blood collection) SLE versus ARD patients, revealing that TIgG (AUC: 0.81) significantly outperforms anti-dsDNA (AUC: 0.72, p = 0.02), EC4d (0.71, p = 0.01), C3 (0.69, p < 0.01), C4 (0.66, p < 0.01) and anti-Smith (0.61, p < 0.01) but not BC4d (0.80, p = 0.84).