What labs are recommended for diagnosing and managing IgA (Immunoglobulin A) nephritis?

Laboratory Tests for IgA Nephropathy: Diagnosis and Management

For diagnosing and managing IgA nephropathy, a comprehensive panel of laboratory tests is essential, including urinalysis with microscopy, proteinuria quantification, kidney function tests, and serological markers to assess disease activity and exclude secondary causes. 1

Initial Diagnostic Evaluation

Essential Laboratory Tests

• Urinalysis with microscopy

  • Assess for glomerular hematuria (dysmorphic red blood cells)
  • Look for red blood cell casts
  • Evaluate for proteinuria by dipstick

• Quantification of Proteinuria

  • 24-hour urine collection for total protein excretion (gold standard) 1
  • First morning urine protein-to-creatinine ratio (PCR) (preferred in pediatric patients) 1
  • Note: Random "spot" urine collections are not ideal due to variation in protein and creatinine excretion 1

• Kidney Function Assessment

  • Serum creatinine
  • Estimated glomerular filtration rate (eGFR)
  • Blood urea nitrogen (BUN)

• Complement Studies

  • C3 and C4 levels (typically normal in primary IgA nephropathy)
  • Low C3 may indicate secondary forms or infection-related glomerulonephritis 1

Exclusion of Secondary Causes

• Serological Tests

  • Hepatitis B surface antigen and core antibody
  • Hepatitis C antibody
  • HIV antibody
  • Antinuclear antibody (ANA)
  • Anti-neutrophil cytoplasmic antibody (ANCA)
  • Anti-glomerular basement membrane (anti-GBM) antibody 1

• Immunological Tests

  • Serum immunoglobulin levels (IgA, IgG, IgM)
  • Rheumatoid factor
  • Cryoglobulins 1

Risk Assessment for Disease Progression

Prognostic Laboratory Markers

• Persistent proteinuria (>1 g/day is a major risk factor) 1
• eGFR at presentation and during follow-up 1
• Time-averaged proteinuria (most important prognostic factor) 1

Monitoring Parameters

• Regular monitoring of proteinuria
  • Target: reduction to <1 g/day 1
• Blood pressure measurements
  • Target: <130/80 mmHg if proteinuria <1 g/day
  • Target: <125/75 mmHg if proteinuria >1 g/day 1
• Serum creatinine and eGFR trends
  • Monitor for decline in kidney function 1

Special Considerations

Pediatric Patients

• First morning PCR is preferred over 24-hour collections 1
• More frequent monitoring may be required 1

Patients with Suspected IgA Vasculitis (Henoch-Schönlein Purpura)

• Additional urinary biomarkers may be helpful:
  • Kidney injury molecule-1
  • Monocyte chemotactic protein-1
  • N-acetyl-β-glucosaminidase
  • Angiotensinogen 2

Monitoring During Treatment

• For patients on immunosuppressive therapy:
  • Complete blood count
  • Liver function tests
  • Drug levels (if applicable)
  • Monitor for medication side effects 1

Kidney Biopsy Indications

While not a laboratory test per se, kidney biopsy is the gold standard for diagnosis and should be considered when:

• Proteinuria >0.5-1 g/day
• Persistent hematuria with any level of proteinuria
• Declining kidney function
• To assess histological features for prognosis (MEST-C score) 1, 3

Follow-up Laboratory Testing

• Frequency: Every 3-6 months initially, then adjusted based on disease activity
• Parameters:
  • Urinalysis with microscopy
  • Quantification of proteinuria (24-hour collection or PCR)
  • Serum creatinine and eGFR
  • Blood pressure monitoring 1

Common Pitfalls to Avoid

• Don't rely solely on dipstick for proteinuria quantification - formal quantification is essential
• Don't assume normal complement levels rule out all secondary causes
• Don't overlook the need for long-term monitoring - even patients with minimal proteinuria at presentation can progress (44% develop adverse events within 7 years) 4
• Don't miss the opportunity for early intervention - patients with hematuria and minimal proteinuria may have significant histological damage and risk of progression 5

By systematically applying these laboratory tests, clinicians can accurately diagnose IgA nephropathy, assess disease severity, monitor progression, and guide therapeutic decisions to improve patient outcomes.