Retrospective Analysis of Membranoproliferative Glomerulonephritis and C3 Behavior in a Large Brazilian Center

Background: Membranoproliferative glomerulonephritis (MPGN) is a disease pattern on kidney biopsy that comprises a series of different diagnostic possibilities. Clinical evaluation and laboratory workup are essential steps on the investigation, although renal biopsy is still mandatory on classification between immunocomplex associated MPGN and C3 glomerulopathy. This study aims to describe the profile of MPGN patients in a large center in Brazil. Methods: Patients with MPGN pattern on kidney biopsy from June 1999 to December 2023 were included. Variables of interest were age, gender, creatinine, estimated glomerular filtration rate (eGFR) by CKD-EPI, proteinuria, intensity of C3 staining on immunofluorescence and serum C3 levels on admission and after 1 year follow-up. Results: A total of 136 renal biopsies were performed on the studied period, 65% of patients were male, 72% white, 46% had hypertension. Mean age was 46 years old (±16), median creatinine 1.8 mg/dL (0.6-15.8) with median eGFR 40 mL/min (4-135), serum albumin 2,7 g/dL (1-4.5), proteinuria 4.6 g (0.1-20.1), 79% hematuria, serum C3 levels 84 (± 39) on diagnosis and 90 (± 34) after a year follow-up. In our cohort 10% of the patients had schistosomiasis, 13% hepatitis C, 4% hepatitis B, 4% HIV and 9% had a paraprotein on immunofixation tests. There was no correlation between C3 levels and initial creatinine and proteinuria, however lower C3 levels were associated with a stronger C3 staining on kidney biopsy (p 0.016) on Kruskal-Wallis test. Additionally, a serum C3 < 80 was not associated with specific biopsy patterns (p 0.25) and immunosuppressive treatment was not an influencing factor on the rise of serum C3. Conclusion: Complement activation is a part of the physiopathological pathway on GNMP, therefore lower serum C3 was observed in patients with stronger C3 staining on kidney tissue showing the association with a higher activation on kidney tissue. Although GNMP can be classified between immunocomplex mediated and C3 glomerulopathy, serum complement levels were not able to identify those patterns.