Proteinuria in PUJ Obstruction with Normal DTPA Findings

Understanding the Clinical Disconnect

Equal split function (50/50) indicates preserved bilateral renal function, which argues against significant chronic obstructive nephropathy from the PUJ obstruction, as suggested by the American College of Radiology 1, 2, 3
Preserved drainage with furosemide suggests the obstruction is not functionally significant at this time, as truly obstructed systems retain radiotracer and cannot increase clearance rate through the narrowed segment, according to Pediatrics 4
PUJ obstruction typically causes proteinuria only when there is significant functional impairment (differential renal function <40%) or progressive deterioration (>5% decline on serial scans), neither of which is present here, as noted by the American College of Radiology 2, 3, 5

Primary glomerular disease (such as IgA nephropathy, focal segmental glomerulosclerosis, membranous nephropathy) should be considered, particularly in an adolescent with isolated proteinuria, as recommended by the American College of Radiology 1
Orthostatic proteinuria is common in adolescents and should be excluded with first-morning urine protein measurements, according to the American College of Radiology 1
Tubular proteinuria from unrelated causes, including medications, infections, or metabolic disorders, should be considered, as suggested by the American College of Radiology 1
Occult vesicoureteral reflux can coexist with PUJ obstruction and cause tubular injury, though this would typically show on imaging, as noted by the American College of Radiology 1

Quantify the proteinuria with 24-hour urine collection or spot urine protein-to-creatinine ratio to determine severity, as recommended by the American Academy of Pediatrics 4
Characterize the proteinuria with urine protein electrophoresis to distinguish glomerular (albumin-predominant) from tubular (low molecular weight proteins) patterns, according to Pediatrics 4
Assess for glomerular disease with serum complement levels, ANA, anti-dsDNA, and ANCA if glomerular proteinuria is confirmed, as suggested by the American College of Radiology 6
Evaluate the contralateral kidney carefully with ultrasound to exclude compensatory hyperfiltration injury or unrecognized pathology, as recommended by the American College of Radiology 5
Consider renal biopsy if proteinuria is significant (>1 g/day) or if there are other features suggesting glomerular disease (hematuria, hypertension, declining GFR), according to Pediatrics 4

Differential renal function falls below 40% on the affected side, as noted by the American College of Radiology 2, 3
Serial scans show >5% functional decline indicating progressive injury, as suggested by the American College of Radiology 2, 3, 5
T1/2 drainage time exceeds 20 minutes despite furosemide, confirming true obstruction, as recommended by the American College of Radiology 2, 3, 6
Bilateral disease or solitary kidney leads to overall renal functional compromise, as noted by the American Academy of Pediatrics 6