The urinary complement C3 concentration was statistically significantly increased in all patients with IgAV compared to patients with SLE (median: IgAV 2.74 μg/mmol [0.15–44.5], SLE 1.52 μg/mmol [0.09–9.66]); p = 0.021), as shown in Fig. 1A. Here, C3 is linked to systemic lupus erythematosus.