Does urinary tract dilation (UTD) contribute to proteinuria in patients, especially those with a history of prenatal diagnosis?

Does UTD Contribute to Proteinuria?

No, urinary tract dilation (UTD) itself does not directly cause proteinuria, but proteinuria can develop as a marker of renal injury in patients with moderate-to-severe UTD who develop chronic kidney disease. 1, 2

Understanding the Relationship Between UTD and Proteinuria

UTD is a structural finding on ultrasound that represents dilation of the renal collecting system, ureters, or bladder. 3 Proteinuria, by contrast, is a functional marker of kidney damage that reflects glomerular or tubular injury. 1 The two are not causally linked in a direct manner—UTD does not produce protein in the urine through the mechanical process of dilation itself. 1, 2

When Proteinuria Develops in UTD Patients

Proteinuria emerges as a consequence of progressive renal injury in children with persistent moderate-to-severe UTD, not from the dilation itself. 1, 2 The mechanism involves:

• Obstructive uropathy: When UTD is caused by conditions like ureteropelvic junction (UPJ) obstruction or posterior urethral valves, chronic obstruction leads to parenchymal damage, fibrosis, and ultimately glomerular injury that manifests as proteinuria. 3

• Reflux nephropathy: In patients with high-grade vesicoureteral reflux (VUR) detected alongside UTD, recurrent pyelonephritis and intrarenal reflux can cause scarring and subsequent proteinuria. 3

• Renal dysplasia: Some children with severe antenatal UTD have underlying renal dysplasia ("reflux nephropathy"), which predisposes to chronic kidney disease and proteinuria independent of UTI history. 3

Evidence on Long-Term Outcomes

In long-term follow-up studies of children with moderate-to-severe UTD, proteinuria is uncommon (0-5%) but occurs almost exclusively in those who develop chronic kidney disease. 1 A 2023 systematic review found that among children with antenatally detected UTD:

• Permanent kidney damage occurs in approximately 40% of children with moderate or severe UTD. 1
• Proteinuria, hypertension, and reduced eGFR remain uncommon overall (0-5% incidence). 1
• Children with mild UTD (UTD P1) have excellent long-term outcomes with essentially no risk of proteinuria. 1

A 2021 cohort study with median 9-year follow-up demonstrated that the probability of developing the composite outcome of "renal injury" (including proteinuria, hypertension, or CKD Stage 2+) at 20 years of age was: 2

• 0% for UTD P1 patients
• 14% for UTD P2 patients
• 56% for UTD P3 patients

This gradient clearly shows that proteinuria risk correlates with UTD severity, but only because severe UTD is associated with underlying pathology that damages the kidney parenchyma. 2

Clinical Implications for Screening

The 2025 American Academy of Pediatrics guidelines on perinatal UTD do not recommend routine urinalysis or proteinuria screening in children with isolated UTD. 3 This is because:

• Low-risk UTD (P1) requires only ultrasound surveillance without additional testing. 3
• Higher-risk UTD (P2-P3) warrants functional imaging (MAG3 scan) and VCUG to identify obstructive uropathy or VUR, not urinalysis for proteinuria. 3
• Proteinuria screening becomes relevant only if chronic kidney disease develops, which is monitored through serial renal function assessment and blood pressure monitoring during nephrology follow-up. 3, 1

Common Pitfalls to Avoid

• Do not assume that finding UTD on ultrasound means the patient has or will develop proteinuria—the vast majority of children with mild-to-moderate UTD will never develop proteinuria. 1, 2

• Do not order routine urinalysis in all UTD patients—this is not indicated by current guidelines and will lead to unnecessary testing and parental anxiety. 3

• Do not confuse UTI risk with proteinuria risk—while UTD increases UTI risk (particularly with ureteral dilation ≥7mm, female gender, or intact foreskin), UTI itself does not typically cause persistent proteinuria unless it leads to renal scarring. 3

• Do recognize that persistent proteinuria in a child with known UTD warrants nephrology referral—this suggests progressive renal injury requiring comprehensive evaluation for chronic kidney disease, hypertension, and potential need for intervention. 3, 1

Practical Algorithm for Proteinuria Assessment in UTD

For children with UTD P1 (low-risk): 3

• No urinalysis or proteinuria screening needed
• Serial ultrasound surveillance only
• Excellent long-term prognosis with 0% risk of renal injury at 20 years 2

For children with UTD P2-P3 (moderate-to-high risk): 3

• Focus on identifying underlying pathology (obstruction, VUR) with VCUG and MAG3 scan
• Nephrology referral for ongoing management
• Monitor blood pressure and renal function during follow-up visits
• Consider urinalysis if CKD develops or if there are clinical concerns for renal injury

If proteinuria is detected in any child with UTD: 1

• Confirm with repeat testing (first morning void protein/creatinine ratio)
• Refer to pediatric nephrology for comprehensive evaluation
• Assess for hypertension, reduced eGFR, and other markers of CKD
• Investigate for progressive obstructive uropathy or reflux nephropathy requiring intervention