The urinary complement C5 concentrations were statistically significantly increased in IgAV patients (median: 0.51 μg/mmol [0.03–6.16]) compared to patients with SLE (0.20 μg/mmol [0.02–1.90]; p = 0.008) (Fig. 1C). This evidence concerns the gene C5 and systemic lupus erythematosus.