What is the appropriate workup for a patient with suspected nephrotic syndrome?

Nephrotic Syndrome Workup

For children under 12 years without syndromic features or family history, start empiric glucocorticoids without biopsy; for all other patients, obtain kidney biopsy and comprehensive laboratory evaluation to determine the underlying cause before initiating immunosuppression. 1

Initial Clinical Assessment

History - Key Elements

• Family history: Consanguinity, ethnicity, early infantile deaths, CNS history, unexplained neurological/kidney disease 2
• Prenatal/perinatal: Enlarged nuchal translucency, elevated amniotic fluid alpha-fetoprotein, fetal edema, placental weight >25% of birth weight 2
• Current symptoms: Fever, pain, abdominal discomfort, edema severity, fatigue 2

Physical Examination Priorities

• Volume status assessment: Distinguish intravascular euvolemia from overload—critical for treatment decisions 2
• Edema distribution: Periorbital, peripheral, ascites, pleural/pericardial effusions 2
• Blood pressure: Target <130/80 mmHg if proteinuria <1 g/day; <125/75 mmHg if >1 g/day 3
• Syndromic features: Skeletal abnormalities, dysmorphic features, genital examination, growth parameters 2

Laboratory Workup

First-Line Blood Tests

• Complete blood count with differential 2
• Comprehensive metabolic panel: Sodium, chloride, creatinine, urea, albumin, total protein 2
• Lipid panel: Total cholesterol, fasting triglycerides 2
• Serum IgG level (assess hypogammaglobulinemia risk) 2
• Thyroid function: TSH, free T4 2
• Bone metabolism: Ionized calcium, phosphate, alkaline phosphatase, PTH, 25(OH) vitamin D3 2

Proteinuria Quantification

Use 24-hour urine collection for adults when initiating immunosuppression or with clinical status changes 4. For children, first morning protein-creatinine ratio is preferred as 24-hour collections are cumbersome and often inaccurate 4. Random spot urine PCR is not ideal due to temporal variation 4.

Secondary Cause Evaluation

Perform targeted serologic testing based on clinical suspicion rather than broad unguided workup 5:

• Diabetes screening: Fasting glucose, HbA1c (most common secondary cause in adults) 6
• Autoimmune: ANA, complement C3/C4 (if lupus suspected) 2
• Infections: Hepatitis B/C, HIV, syphilis (if risk factors present) 2
• Membranous nephropathy: Anti-PLA2R antibodies (if positive, diagnostic—biopsy may be avoided) 4, 7
• Vasculitis: MPO-ANCA, PR3-ANCA (if clinical suspicion) 4

Critical caveat: Routine serologic panels without clinical suspicion do not improve diagnostic accuracy and are rarely abnormal 5. Target testing based on history and examination findings.

Imaging Studies

Renal Ultrasound - Mandatory

• Kidney size and echogenicity: Small kidneys suggest chronicity; increased echogenicity may indicate glomerulonephritis 8
• Pre-biopsy assessment: Essential for safe biopsy planning 8
• Complications screening: Renal vein thrombosis, ascites, pleural effusions 2

Cardiac Ultrasound

Evaluate for pericardial effusions and left ventricular mass changes 2

Kidney Biopsy Decision Algorithm

Biopsy NOT Required:

• Children <12 years, no syndromic features, no family history → Start empiric glucocorticoids 1
• Adults with positive anti-PLA2R antibodies (diagnostic of membranous nephropathy) 4
• Well-characterized familial FSGS with known mutations 4
• Biopsy contraindicated by coagulopathy or other factors 4

Biopsy REQUIRED:

• All children ≥12 years at presentation 1
• Children <12 years with syndromic features or positive family history 1
• Children <12 years who fail to respond to 4-6 weeks of glucocorticoids 1
• All adults (except those with positive PLA2R antibodies) 7, 6
• Any patient with rapidly declining kidney function 3

Biopsy Adequacy Standards

Tissue must include 4:

• Light microscopy: Minimum 8-10 glomeruli for confident diagnosis
• Immunofluorescence: IgG, IgA, IgM, C3, C4, C1q, kappa/lambda light chains
• Electron microscopy: Assess deposits, foot process effacement (>70% suggests primary disease), GBM structure 3

Age-Specific Considerations

Children (<12 years)

Start daily prednisone/prednisolone 1 mg/kg (max 80 mg) or alternate-day 2 mg/kg (max 120 mg) for 4-6 weeks without biopsy 1. If complete response occurs, continue taper over 6 months 3. If no response after 4-6 weeks, proceed to genetic testing and kidney biopsy 1.

Adults

Always pursue biopsy for histologic diagnosis unless PLA2R-positive 7. The most common causes are FSGS, membranous nephropathy, and diabetic nephropathy 6. Secondary causes predominate, making histologic confirmation essential for treatment decisions 9.

Genetic Testing Indications

Order genetic testing for 2, 1:

• Congenital or infantile-onset nephrotic syndrome
• Steroid-resistant nephrotic syndrome in children
• Positive family history of nephrotic syndrome
• Syndromic features present
• Before considering immunosuppression in young children with SRNS

Common Pitfalls to Avoid

1. Do not delay referral to pediatric nephrology for congenital cases—these children require specialized management 2
2. Do not perform routine broad serologic panels—target testing based on clinical suspicion 5
3. Do not use random spot urine PCR for treatment decisions—obtain 24-hour collection or first morning void 4
4. Do not biopsy children <12 years empirically—treat first, biopsy only if steroid-resistant 1
5. Do not assume CNI nephrotoxicity in patients with rising creatinine—consider disease progression, drug interactions, or other complications first 3