Lower proteinuria is better for patients with IgA nephropathy: a systematic review

Background: Proteinuria is a well-established and recommended biomarker for disease activity in patients with IgAN. In the most recent version of the KDIGO guideline, the target level of proteinuria changed from < 1.0 g/day to < 0.5 g/day. The objective of this systematic literature review (SLR) is to identify, synthesize, and critically evaluate the evidence from peer-reviewed publications that inform the significance of achieving different proteinuria levels. Methods: protocol following established methodological guidance for systematic reviews. Additionally, the quality of all studies included in the SLR was assessed based on standardized appraisal tools. The evidence was narratively synthesized reporting frequencies and percentages. Results: Twenty-one unique studies were included (representing 13,006 patients with IgAN). The studies captured in the SLR were mostly observational and they encompassed diverse patient populations, timing of proteinuria assessment, methods of proteinuria measurement and classification, and clinical management strategies, reflecting real-world heterogeneity in IgAN. Despite the differences in individual study methods, results across studies consistently found that lower proteinuria was associated with better kidney outcomes. Specifically, it was clearly established that