What labs are used to test for nephrotic syndrome?

Laboratory Tests for Nephrotic Syndrome

The essential laboratory tests for diagnosing nephrotic syndrome include quantitative measurement of proteinuria, serum albumin, lipid panel, and urinalysis with microscopy. 1

Core Diagnostic Tests

Proteinuria Assessment

• 24-hour urine collection to determine total protein excretion (gold standard)
  • Nephrotic-range proteinuria defined as >3.5 g/24 hours in adults 2, 3
  • For children, first morning protein-creatinine ratio (PCR) is more appropriate 1
  • PCR >300-350 mg/mmol indicates nephrotic range proteinuria 3

Serum Tests

• Serum albumin (hypoalbuminemia <30 g/L is diagnostic) 3
• Lipid panel (hyperlipidemia, especially hypercholesterolemia and hypertriglyceridemia) 2
• Complete blood count with differential 4
• Serum creatinine and BUN to assess kidney function 1, 4
• Serum electrolytes including sodium, chloride, and calculated anion gap 4

Urinalysis

• Urinalysis with microscopy to evaluate for:
  • Proteinuria
  • Hematuria (>50 RBCs/HPF)
  • Casts (especially red cell casts)
  • Lipiduria 1, 4

Additional Diagnostic Tests

Serologic Studies

• Anti-PLA2R antibodies (for membranous nephropathy diagnosis) 1, 5
• Serum complement (C3 and C4) (for lupus nephritis) 1
• Anti-nuclear antibodies (ANA) 1
• ANCA (for vasculitis) 1
• Anti-GBM antibodies 1
• Serum free light chains 1
• Serum and urine protein electrophoresis/immunofixation 1

Infectious Disease Screening

• Hepatitis B and C serology 1
• HIV testing 1
• Syphilis screening 1
• Other infection screening based on clinical suspicion and endemic areas 1

Imaging Studies

• Renal ultrasound to assess kidney structure (size, shape, symmetry, and evidence of obstruction) 1, 4
• Cardiac ultrasound if cardiac effusion is suspected 1

Diagnostic Confirmation

• Kidney biopsy is the gold standard for determining the underlying cause of nephrotic syndrome 1
  • May be deferred in children who respond to steroids (likely minimal change disease) 5
  • May be deferred in adults with positive anti-PLA2R antibodies (diagnostic of membranous nephropathy) 5

Common Pitfalls

• Failing to obtain quantitative measurement of proteinuria (relying only on dipstick)
• Not checking serum albumin, which is essential for diagnosis
• Missing secondary causes by inadequate serologic testing
• Delaying kidney biopsy in adults, which is usually indicated for diagnosis and treatment planning 3, 5

Special Considerations

• In children, genetic testing should be considered, especially in steroid-resistant cases 1
• In adults with diabetes, diabetic nephropathy should be considered as a common cause 3
• Thrombotic risk assessment is important as nephrotic syndrome increases risk of venous thromboembolism 1, 6

Following this systematic laboratory approach will help establish the diagnosis of nephrotic syndrome and guide appropriate management based on the underlying cause.