#627 C3 glomerulonephritis and C3-dominant infection related glomerulonephritis—are they similar?

Abstract Background C3 glomerulonephritis (C3GN) and C3 dominant infection related glomerulonephritis (C3-IRGN) comprise two important immune complex mediated diseases. C3GN is caused by dysregulation of the alternate pathway by congenital or acquired abnormalities in the complement pathway. C3-IRGN is often preceded by infection followed by recovery after the infection resolves. Although kidney biopsy findings may be similar in both conditions, the clinical course and treatment differs. We aimed to compare the demographic, clinical and lab parameters of C3GN and C3-IRGN. Methods All kidney biopsies conducted at Institute of Nephrourology, Bengaluru with dominant C3 on immunofluorescence from Jan. 2019-Dec. 2022 were included. The diagnosis of C3-IRGN was established using established criteria. Patients with C3GN had persistently low C3 for more than 12 weeks and no identifiable source of infection. Patients with C3GN were treated with steroids and cyclophosphamide, while those with C3-IRGN received antibiotics along with supportive medical management (including renin-angiotensin-aldosterone inhibition). Demographic, clinical and lab parameters were recorded and compared. Results 23 cases of C3-IRGN and 19 cases of C3GN were included in the study. The mean duration of follow-up was 2.79 ± 0.92 years for those with C3GN and 2.78 ± 0.90 years for those with C3-IRGN. C3GN was common in younger patients (second decade of life) while C3-IRGN was common in the fourth and fifth decades of life. C3GN (57.9%) and C3-IRGN (73.9%) were both common in males. Previous infection (26.1% vs 5.3%) and present infection (39.1% vs 15.8%) were significantly more common in C3-IRGN. Hematuria (52.6% vs 34.8%), patient reported “frothy” urine (47.4% vs 21.7%) was significantly more common in C3GN compared to C3-IRGN. 36.8% of patients with C3GN had IFTA of 50% compared to only 8.7% in C3-IRGN. Patients with both conditions most commonly presented with either acute nephritic syndrome or rapidly progressive glomerulonephritis. In contrast, presentation with CKD was significantly more common in C3GN (36.8% vs 0%, P = 0.002) compared to C3-IRGN, and patients with C3GN were more likely to require kidney replacement therapy (47.4% vs 21.7%, P = 0.002). At the end of follow up, 65.2% of patients with C3-IRGN attained complete recovery, compared with only 47.4% of C3GN patients. Conclusion There are characteristic differences between individuals with C3-IRGN and C3GN that may help to better ascertain diagnosis at presentation. Patients with C3GN tend to have worse prognosis, emphasizing the importance of treatments to slow CKD progression and avoid the need for kidney replacement therapy.