Serum IgA Levels in IgA Nephropathy
Serum IgA levels are NOT reliably increased in IgA nephropathy and cannot be used to diagnose the disease. According to the most recent KDIGO 2025 guidelines, there are no validated diagnostic serum or urine biomarkers for IgAN, and the diagnosis can only be made by kidney biopsy 1.
Key Clinical Points
Why Serum IgA is Unreliable for Diagnosis
The KDIGO 2025 guideline explicitly states that kidney biopsy is the only way to diagnose IgAN and that no validated serum biomarkers exist for diagnosis 1. This is critical because:
- While some patients with IgAN may have elevated serum IgA levels, this finding is neither sensitive nor specific enough for clinical diagnosis
- The pathology of IgAN involves mesangial deposition of IgA-containing immune complexes, not necessarily elevated circulating IgA
- Secondary causes of IgA deposition (cirrhosis, inflammatory bowel disease, infections) must be excluded 2
What the Research Shows (But Why It Doesn't Change Practice)
Older research studies from the early 2000s suggested that:
- Serum IgA levels >315 mg/dL combined with other markers (hematuria, proteinuria, IgA/C3 ratio >3.01) could help distinguish IgAN from other glomerular diseases 3, 4
- Approximately 30-76% of IgAN patients may have elevated serum IgA 5
- However, polymeric IgA levels relative to total IgA are actually lower in IgAN patients 6
These findings have NOT been validated or incorporated into current clinical practice guidelines. The 2025 KDIGO guideline makes no mention of serum IgA as a diagnostic tool, emphasizing instead that biopsy remains mandatory 1.
Clinical Approach
When to Suspect IgAN
- Persistent microscopic hematuria with proteinuria ≥0.5 g/day
- Synpharyngitic hematuria (visible hematuria with upper respiratory infections)
- Nephritic syndrome in younger adults (mean age 34-45 years) 2
Diagnostic Pathway
- Quantify proteinuria and assess kidney function (eGFR)
- Exclude secondary causes (lupus, hepatitis, cirrhosis, inflammatory bowel disease)
- Proceed to kidney biopsy if proteinuria ≥0.5 g/day and IgAN is suspected 1
- Do NOT rely on serum IgA levels for diagnosis
What Actually Matters for Prognosis
The only validated biomarkers for IgAN prognosis are:
- Proteinuria levels (goal <0.5 g/day, ideally <0.3 g/day)
- eGFR and rate of decline (goal <1 mL/min/1.73m² per year)
- Histologic MEST-C scoring on biopsy 1
Common Pitfall
Do not order serum IgA levels to "rule in" or "rule out" IgA nephropathy. This is a waste of resources and may delay appropriate diagnosis. A normal serum IgA does not exclude IgAN, and an elevated serum IgA does not confirm it. The diagnosis requires tissue confirmation with demonstration of IgA-dominant mesangial immune deposits 2.