Abstract
Background and Aims
Considerable knowledge gaps exist in our understanding of the natural history of C3 glomerulopathy (C3G). Disease rarity, multiple nomenclature changes, and the inclusion of dissimilar cases in historical cohorts have precluded retrospective studies to define the natural course of C3G and identify risks for progression to kidney failure (end stage renal disease/ESRD). In the present analysis, we focus on C3G patients with native kidneys and examine the relationship between reductions in UPCR and disease progression as indicated by changes in eGFR.
Method
Patients included in this study were consented and enrolled in the University of Iowa C3G ReCom Registry, which was created in 2013. Beginning in 2017, complement activity and renal function data were collected prospectively at approximately 6-month intervals to define the natural history of C3G. Analyses were performed across 1-year periods of time (“spans”). To be included in a span, a patient had to meet the following criteria at the start of the 1-year period: native C3G, eGFR ≥30 mL/min/1.73 m2, UPCR ≥1 g/g and ≥12 years of age. An individual patient could be included in more than one span.
Results
Analyses were performed using 34 one-year spans for 24 patients who met inclusion criteria at the beginning of the 1-year span. Baseline characteristics for the 34 spans were: male, 59%; mean age, 22.7 years; mean eGFR, 83.1 ml/min/1.73m2; mean UPCR, 2.86 g/g; mean plasma C3, 75.1 mg/dL.
Similar analyses using only the first 1-year span for each of the 24 patients produced results that were consistent with those generated using all 1-year spans. Limitations of this study include its small sample size and data variability due to its observational nature.
Conclusion
The findings of this observational study support the premise that reductions in proteinuria are associated with a more stable eGFR in native kidney C3G. Regression analyses using UPCR as a continuous variable demonstrate the relationship between reduction in UPCR and preservation of eGFR. This association was also observed using both change in eGFR by UPCR reduction subgroup and UPCR-eGFR categorical analyses.
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