Early detection of proteinuria to prevent kidney fibrosis and progression to kidney failure: lessons from the School Urine Screening Program in Japan

Chronic kidney disease (CKD) represents a growing global health challenge, often progressing silently until advanced stages. Persistent proteinuria plays a pivotal role in initiating the fibrotic niche-a complex cellular microenvironment contributing to early kidney fibrosis and closely associated with kidney failure. Despite advancements in CKD management, proteinuria remains underrecognized as a critical surrogate endpoint for disease progression. Urine screening for proteinuria in asymptomatic pediatric populations has been contentious due to concerns about diagnostic reliability, cost-effectiveness, and clinical relevance. However, recent data from Japan present a contrasting perspective. With a well-established nationwide school-based urine screening program, Japan has demonstrated effective early detection and intervention strategies, particularly for conditions such as IgA nephropathy. A 2024 economic evaluation reported an incremental cost-effectiveness ratio well below Japan's pediatric willingness-to-pay threshold, affirming the program's economic and clinical viability. These findings underscore the potential of structured screening protocols-especially in regions with underreported disease prevalence or limited healthcare access-to prevent long-term kidney impairment. Modifiable factors such as screening frequency, age of initiation, and integration of emerging biomarkers must be considered to optimize outcomes. This review highlights the need to revisit the role of proteinuria screening in pediatric nephrology, advocating for evidence-informed policy decisions that recognize its long-term value. Japan's model offers a robust framework for balancing cost, clinical impact, and public health priorities in global efforts to address CKD in its earliest stages.