C4A and acute kidney injury: Within the Hungarian cohort, severe AKI patients more frequently had below normal alternative pathway activity (63.6 vs. 23.0%; p = 0.03), classical pathway activity (36.4 vs. 9.2%; p = 0.04), as well as above normal C4 levels (27.3 vs. 4.6%; p = 0.04), and C3a levels (81.8 vs. 39.1%; p = 0.01).