Long-Term Risk of ESKD in Postinfectious Glomerulonephritis

Background: Kidney biopsy is usually not required for the diagnosis of post-infectious glomerulonephritis (PIN). When kidney biopsies are nevertheless performed for example in patients with PIN and severe or atypical clinical presentations, the light microscopic picture is characteristic in the form of endocapillary glomerulonephritis. The immunological picture is however less specific for PIN as in many cases this is dominated by complement factor C3 deposits. In such cases, PIN can theoretically be confused with complement 3 nephropathy (C3N) based on the immunological findings. While PIN is considered a self-limiting condition with a good prognosis, C3N, often has a progressive course leading to end-stage kidney disease (ESKD) in a significant proportion of patients. To what extent confusion of PIN versus C3N has occurred in clinical practice in Norway is unknown. As such prognostic data is limited we have analyzed the very long-term risk of ESKD in patients with biopsy-verified PIN registered in the Norwegian Kidney Biopsy Registry (NKBR) in the period 1991-2012. Methods: Cases of biopsy-verified PIN 1991-2012 including demographic, clinical, laboratory, and histological variables at the time of diagnosis were retrieved from the NNBR. The cohort was linked with the Norwegian Kidney Registry for identification of patients with ESKD by May 1, 2024. Results: We identified 82 patients with PIN. Men; 45 (55%), age; 35 years (SD 22), systolic BP; 140 mmHg (SD 24), diastolic BP; 80 (SD 14), hypertension 42 (51%), eGFR 58 ml/min/1.73m2 (SD 37), eGFR<15; 12 (15%), eGFR 15-29; 8 (10%) and eGFR 30-59; 26 (32%), serum albumin; 31 gram/liter (SD 6), proteinuria; 3.8 gram/24 hours (SD 4.2), nephrotic syndrome; 20 (24%), crescents; 26 (32%), >50% tubulointerstitial fibrosis; 17 (21%) and isolated C3 positivity 29 (35%). During an average observation time of 21 years, there were no patients who progressed to ESKD. Conclusion: Despite many cases with severe kidney affection at the time of diagnosis, no patients with PIN progressed to ESKD during a very long follow-up time. A C3N resembling immunological image is not associated with the risk of ESKD in patients with PIN. Funding: Commercial Support - Novartis