When comparing these patients defined as having idiopathic hypocryoglobulinaemia with patients of a historic cohort of mixed cryoglobulinaemia-associated nephritis described by our group14, we found a significantly lower prevalence of HCV+ (27% vs. 87%, p < 0.001), RF+ (35% vs. 97%, p < 0.001), and C4 consumption (37% vs. 97%, p < 0.001) in the group with idiopathic hypocryoglobulinaemia. Here, C4A is linked to nephritis.