What are the initial laboratory tests for a patient with suspected IgA (Immunoglobulin A) Nephropathy?

Initial Laboratory Workup in IgA Nephropathy

For suspected IgA nephropathy, obtain serum creatinine with eGFR calculation, comprehensive urinalysis with albumin-to-creatinine and protein-to-creatinine ratios, complete blood count, and basic metabolic panel including bicarbonate, chloride, phosphate, and uric acid. 1

Core Laboratory Tests

Kidney Function Assessment

• Serum creatinine with creatinine-based eGFR calculation to establish baseline renal function 1
• Serial measurements are critical, as eGFR decline >2 mL/min/1.73m² per year indicates progressive disease requiring biopsy 1

Urinalysis Panel

• Dipstick urinalysis to detect hematuria and proteinuria 1
• Albumin-to-creatinine ratio (ACR) - values >30 mg/mmol warrant kidney biopsy consideration 1
• Protein-to-creatinine ratio (PCR) - essential for quantifying proteinuria severity 1
• Persistent proteinuria >1 g/day is the single most important predictor of poor outcomes in IgA nephropathy 2

Metabolic Parameters

• Serum bicarbonate, chloride, phosphate, and uric acid levels to assess for tubular dysfunction 1
• Hypouricemia may suggest Fanconi syndrome, which would prompt biopsy 1

Complete Blood Count

• CBC with differential to evaluate for anemia and systemic involvement 1

Additional Diagnostic Considerations

Serum IgA Levels

• Serum IgA levels >315 mg/dL combined with serum IgA/C3 ratio >3.01 can support the diagnosis of IgA nephropathy, though these are not definitive without biopsy 3
• Elevated serum IgA occurs in approximately 50% of IgA nephropathy cases but is not specific 3

Complement Levels

• Serum C3 measurement to calculate IgA/C3 ratio and assess for complement-mediated disease 3

Critical Clinical Context

Hematuria Patterns

• Document whether hematuria is episodic gross hematuria (occurs in 40-50% of cases, often following upper respiratory infections) or persistent microscopic hematuria 4
• The presence of >5 red blood cells in urinary sediment is a key diagnostic marker 3

Blood Pressure

• Measure blood pressure, as uncontrolled hypertension is an independent predictor of adverse outcomes and may precede renal insufficiency 2, 5

Exclusion of Secondary Causes

Before proceeding to biopsy, assess for conditions that can cause secondary IgA deposition:

• Liver function tests to exclude cirrhosis and chronic liver disease 4
• Consider screening for systemic lupus erythematosus (ANA, anti-dsDNA) 4
• Evaluate for inflammatory bowel disease if gastrointestinal symptoms present 4

Biopsy Indications Based on Laboratory Findings

Kidney biopsy is advised when laboratory workup reveals:

• eGFR <60 mL/min/1.73m² with >2 mL/min/1.73m² per year decline 1
• Proteinuria with hematuria 1
• Albumin-to-creatinine ratio >30 mg/mmol 1
• AKI stage 3 1

Consider biopsy when:

• eGFR <60 mL/min/1.73m² with <2 mL/min/1.73m² per year decline 1
• Albumin-to-creatinine ratio 3-30 mg/mmol with eGFR >60 mL/min/1.73m² 1
• Hematuria with eGFR <60 mL/min/1.73m² 1

Common Pitfalls

• Do not rely on clinical features alone to exclude IgA nephropathy, as presentation overlaps significantly with thin basement membrane disease and Alport syndrome 4
• Do not dismiss mild proteinuria (<1 g/day) - while associated with excellent prognosis, it still requires monitoring as it rarely progresses to higher levels 5
• Recognize that proteinuria may fluctuate markedly in patients with preserved renal function, so single measurements may not reliably predict outcome 6
• Any proteinuria >0.5 g/day warrants cardiovascular risk assessment independent of renal function 2