Residency · Residency · Medicine Pediatrics
Approach to Proteinuria in Children and Adults
Introduction
Proteinuria is a hallmark of kidney disease and a critical marker for cardiovascular risk. In children, the most common cause of nephrotic-range proteinuria is minimal change disease, while in adults, diabetic nephropathy and focal segmental glomerulosclerosis (FSGS) predominate. The evaluation and management differ by age, with particular attention to distinguishing benign causes from progressive glomerular disease. Med-peds physicians must systematically approach proteinuria across the lifespan.
Definitions and Quantification
Normal Protein Excretion
Normal urine protein excretion: <150 mg/day in adults; <4 mg/m2/hour in children. Albumin is the predominant pathologic protein; normally <30 mg/day.
Levels of Proteinuria
Microalbuminuria (moderately increased albuminuria): 30-300 mg/day; early marker of diabetic and hypertensive nephropathy. Overt proteinuria: >300 mg/day. Nephrotic-range proteinuria: >3.5 g/day in adults; >40 mg/m2/hour or urine protein-to-creatinine ratio (UPCR) >2.0 mg/mg in children.
Methods of Measurement
Urine dipstick: Detects albumin; semi-quantitative; does not detect light chains or low-molecular-weight proteins. Spot urine protein-to-creatinine ratio (UPCR): Correlates with 24-hour excretion; normal <0.2 mg/mg in children >2 years; <0.5 in infants. Spot urine albumin-to-creatinine ratio (UACR): Preferred for diabetic nephropathy screening; normal <30 mg/g. 24-hour urine collection: Gold standard but cumbersome; useful for quantifying total protein and specific proteins.
Benign Causes of Proteinuria
Transient Proteinuria
Caused by fever, exercise, dehydration, emotional stress, seizures. Resolves with elimination of the inciting factor. No further workup needed if repeat urinalysis is normal.
Orthostatic Proteinuria
Most common cause of persistent proteinuria in adolescents and young adults. Proteinuria present only in the upright position; absent in first morning void. Diagnosed with split urine collection: first morning void (supine) vs. daytime specimen. Benign condition; does not require treatment or biopsy. Prevalence: up to 2-5% of adolescents; rare over age 30.
Pathologic Causes of Proteinuria
| Cause | Age Group | Frequency | Steroid Response | Biopsy Needed? |
|---|---|---|---|---|
| Minimal change disease | Children 1-10 years | Most common (80%) | >90% responsive | Not if typical presentation |
| FSGS | Older children/adults | Common | Often resistant | Yes |
| Membranous nephropathy | Adults (White) | Most common primary NS in adults | N/A | Yes (anti-PLA2R can support) |
| Diabetic nephropathy | Adults | Most common overall cause | N/A | Not if typical diabetes + retinopathy |
| IgA nephropathy | All ages | Most common GN worldwide | N/A | Yes |
| Lupus nephritis | Young adults/adolescents | Important secondary cause | N/A | Yes (ISN/RPS classification) |
Pediatric Causes
Minimal change disease (MCD): Most common cause of nephrotic syndrome in children (80% of cases aged 1-10 years) Presents with edema, massive proteinuria, hypoalbuminemia, hyperlipidemia. Steroid-responsive in >90% of cases; empiric steroid trial without biopsy in typical presentations (age 1-12, no hypertension, no hematuria, normal complement, normal renal function) Frequent relapses are common; steroid-sparing agents (cyclophosphamide, calcineurin inhibitors, rituximab) for steroid-dependent disease. FSGS: More common in older children and adolescents; often steroid-resistant; higher risk of progression to ESRD. Membranous nephropathy: Rare in children; when present, consider secondary causes (lupus, hepatitis B) IgA nephropathy: Hematuria with variable proteinuria. Congenital nephrotic syndrome: Presents in the first 3 months of life; genetic causes (NPHS1, NPHS2 mutations)
Adult Causes
Diabetic nephropathy: Most common cause of CKD and proteinuria in adults; microalbuminuria is the earliest marker. FSGS: Most common primary glomerular disease causing nephrotic syndrome in adults in the U.S.; associated with obesity, HIV, genetic variants (APOL1) Membranous nephropathy: Most common cause of primary nephrotic syndrome in White adults; anti-PLA2R antibodies in ~70%. IgA nephropathy: Most common glomerulonephritis worldwide; hematuria with proteinuria. Lupus nephritis: Proteinuria with active urine sediment; requires renal biopsy for classification. Amyloidosis: Consider in adults with nephrotic-range proteinuria and systemic symptoms; AL and AA types. Multiple myeloma: Light chain proteinuria; dipstick-negative (does not detect light chains); detected by urine protein electrophoresis.
Evaluation
Initial Workup (Both Populations)
Confirm proteinuria on repeat specimen (rule out transient causes) First morning UPCR: Confirms or excludes orthostatic proteinuria. Complete urinalysis with microscopy: Assess for hematuria, casts, cellular elements. Serum albumin, creatinine, BUN, lipid panel. Complete blood count and comprehensive metabolic panel.
Additional Studies
Complement levels (C3, C4): Low in PIGN, MPGN, lupus nephritis. ANA, anti-dsDNA, ANCA: For suspected autoimmune disease. Hepatitis B and C serology: Associated with membranous and MPGN. HIV testing: Associated with FSGS (collapsing variant) Anti-PLA2R antibodies: For suspected primary membranous nephropathy in adults. Serum and urine protein electrophoresis (SPEP/UPEP): For suspected myeloma or amyloidosis. Renal ultrasound: Assess kidney size, echogenicity, and structure.
Kidney Biopsy Indications
Children: Atypical nephrotic syndrome (age <1 or >12, hematuria, hypertension, low complement, renal insufficiency, steroid resistance) Adults: Most cases of nephrotic syndrome require biopsy for diagnosis (except clear diabetic nephropathy in the setting of established diabetes with retinopathy) Biopsy guides treatment and prognosis.
Management Principles
Non-Specific Measures (All Patients)
ACE inhibitors or ARBs: First-line antiproteinuric therapy; reduce intraglomerular pressure and proteinuria by 30-50%. SGLT2 inhibitors: Significant renoprotective benefit in adults with proteinuric CKD (DAPA-CKD, EMPA-KIDNEY trials); emerging pediatric data. Blood pressure control: Target <130/80 in adults with proteinuria; age-appropriate targets in children. Dietary sodium restriction: <2 g/day to enhance efficacy of RAAS blockade. Statin therapy: For persistent hyperlipidemia in nephrotic syndrome.
Disease-Specific Treatment
Minimal change disease: Prednisone 2 mg/kg/day (max 60 mg) for 4-6 weeks, then taper; steroid-sparing agents for frequent relapsers. FSGS: Prolonged steroid trial (16 weeks), calcineurin inhibitors for steroid-resistant disease; rituximab for refractory cases. Membranous nephropathy: Observation for low-risk; rituximab or cyclophosphamide-based regimens for high-risk (Ponticelli protocol) Diabetic nephropathy: Optimize glycemic control, RAAS blockade, SGLT2 inhibitors, finerenone (mineralocorticoid receptor antagonist) Lupus nephritis: Mycophenolate or cyclophosphamide induction; maintenance with mycophenolate.
Clinical Pearls
Orthostatic proteinuria is the most common cause of persistent proteinuria in adolescents; a first morning UPCR <0.2 confirms the diagnosis. In children aged 1-10 with typical nephrotic syndrome, empiric steroid therapy without biopsy is standard; atypical features warrant biopsy. ACE inhibitors/ARBs are first-line antiproteinuric therapy in both populations; SGLT2 inhibitors provide additional renoprotection in adults. Dipstick urinalysis does not detect light chain proteins; SPEP/UPEP is essential when myeloma is suspected. Proteinuria >1 g/day in adults is an independent risk factor for CKD progression and cardiovascular events.
References
- Kidney Disease: Improving Global Outcomes (KDIGO) Glomerulonephritis Work Group. KDIGO clinical practice guideline for glomerulonephritis. Kidney Int Suppl. 2021;100(4S):S1-S276.
- Nephrotic syndrome in children: Prediction of histopathology from clinical and laboratory characteristics at time of diagnosis. Kidney Int. 1978;13(2):159-165.
- Heerspink HJL, Stefansson BV, Correa-Rotter R, et al. Dapagliflozin in patients with chronic kidney disease (DAPA-CKD). N Engl J Med. 2020;383(15):1436-1446.
- Vivarelli M, Massella L, Ruber B, et al. Is the long-term outcome of childhood nephrotic syndrome improving? Nephrol Dial Transplant. 2017;32(10):1674-1681.