What are the diagnostic criteria for nephritic syndrome?

Diagnostic Criteria for Nephritic Syndrome

Nephritic syndrome is diagnosed by the presence of hematuria, proteinuria (typically sub-nephrotic range), hypertension, and often acute kidney injury with fluid retention, distinguishing it from nephrotic syndrome which requires heavy proteinuria >3.5 g/day, hypoalbuminemia <3.0 g/dL, and edema 1, 2.

Core Diagnostic Features

The nephritic syndrome constellation includes:

• Hematuria (often with red blood cell casts on urinalysis)
• Proteinuria (usually <3.5 g/24 hours, though can overlap with nephrotic range)
• Hypertension (a key distinguishing feature from nephrotic syndrome)
• Acute kidney injury (elevated creatinine, reduced GFR)
• Fluid retention (edema, oliguria)

Critical Distinction from Nephrotic Syndrome

This distinction is clinically essential because it fundamentally changes your diagnostic approach and prognosis:

Nephrotic syndrome requires:

• Heavy proteinuria >3.5 g/24 hours
• Hypoalbuminemia <3.0 g/dL
• Peripheral edema
• Often hyperlipidemia and hypercoagulability

Nephritic syndrome is characterized by:

• Inflammatory glomerular injury pattern
• Hematuria as the dominant feature
• Proteinuria present but typically less severe
• Hypertension (often absent in pure nephrotic syndrome)
• Poorer prognosis with risk of progressive kidney dysfunction 2

Common Etiologies to Evaluate

When you identify nephritic syndrome, systematically evaluate for these most common causes 1, 2:

• Post-infectious glomerulonephritis (especially post-streptococcal)
• IgA nephropathy (most common globally, particularly in East Asia where it comprises ~50% of cases) 3
• Lupus nephritis
• ANCA-associated vasculitis
• Membranoproliferative glomerulonephritis

Clinical Pitfall

The most common error is confusing nephritic with nephrotic syndrome. The presence of hypertension and hematuria with relatively preserved albumin levels points toward nephritic syndrome, even if proteinuria is in the nephrotic range 2. Nephritic syndrome carries a worse prognosis with higher risk of progressive kidney disease, making accurate classification critical for appropriate urgency of workup and referral to nephrology.

Diagnostic Workup Algorithm

When nephritic syndrome is suspected:

1. Confirm the syndrome: Urinalysis showing hematuria with RBC casts, quantify proteinuria (24-hour collection or protein/creatinine ratio), check serum creatinine and albumin
2. Assess severity: Blood pressure, degree of kidney dysfunction, fluid overload status
3. Identify etiology: Complement levels (C3, C4), ANA, ANCA, anti-GBM antibodies, ASO titers, hepatitis and HIV serologies, serum and urine protein electrophoresis
4. Kidney biopsy: Essential for definitive diagnosis in most cases, particularly when diagnosis remains unclear or to guide immunosuppressive therapy 3

Nephritic syndrome represents approximately 21% of kidney biopsy indications, with IgA nephropathy being the single most frequent diagnosis at 38% of cases 3.