Nephrotic Syndrome Diagnostic Criteria

Introduction to Nephrotic Syndrome

Nephrotic syndrome is defined by proteinuria ≥3.5 g/24 hours in adults and ≥40 mg/m²/hour (or spot urine protein-to-creatinine ratio ≥2 g/g) in children, accompanied by hypoalbuminemia and edema, as recommended by the Kidney International guidelines 1, 2

The American College of Cardiology and Kidney International guidelines recommend that proteinuria ≥3.5 g/24 hours is the standard diagnostic criterion for nephrotic syndrome in adults, with a strength of evidence level of high 1, 2
Patients with proteinuria >3.8 g/day face a 35% risk of end-stage renal disease within 2 years, compared to only 4% risk for those with proteinuria <2.0 g/day, according to the Kidney International guidelines 1, 3

The American Academy of Pediatrics and American Journal of Kidney Diseases guidelines recommend that children require different proteinuria thresholds adjusted for body surface area, with ≥40 mg/m²/hour on timed urine collection or first morning spot urine protein-to-creatinine ratio ≥2 g/g 1, 4, 5
The spot UPCR has replaced 24-hour collections as standard of care in children due to good correlation and practical advantages, as recommended by the American Journal of Kidney Diseases guidelines 4, 5

The Kidney International guidelines recommend that proteinuria alone is insufficient for diagnosis, and the complete syndrome requires proteinuria ≥3.5 g/24 hours, serum albumin <3.0 g/dL, and edema in adults 1, 2
The American Journal of Kidney Diseases guidelines recommend that in children, the complete syndrome requires proteinuria ≥40 mg/m²/hour or UPCR ≥2 g/g, serum albumin ≤2.5 g/dL, and edema 4, 5

The Kidney International and American Journal of Kidney Diseases guidelines recommend that albumin assay variability matters clinically, and a serum albumin of 2.5 g/dL measured by BCG equals approximately 2.0 g/dL by BCP 2, 4
The KDOQI US Commentary recommends maintaining the traditional ≤2.5 g/dL threshold for pediatric albumin, reflecting 50 years of clinical trial data using the lower threshold, with a strength of evidence level of moderate 4, 5
The Kidney International guidelines define relapse as proteinuria >3.5 g/day after achieving complete remission for >1 month in adults, with complete remission defined as proteinuria <0.2 g/day with serum albumin >35 g/L 1, 3