C3 and membranoproliferative glomerulonephritis: With this paper, we would like to raise awareness that even if APIGN is the leading cause of acute nephritis with low C3 levels in young children and kidney biopsy is not required in typical cases, there are some red flags suggesting differential diagnoses such as C3 glomerulopathy, membranoproliferative glomerulonephritis, or, as in this case, cSLE, requiring prompt and appropriate treatment and indicating a biopsy (Oni et al. [26]).