Nephrology

Nephritic Syndrome - Overview song

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Nephritic Syndrome - Overview

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Nephritic syndrome is characterized by the triad of hematuria (RBC casts in urine), hypertension, and oliguria with mild-to-moderate proteinuria (typically <3.5 g/day).
RBC casts are pathognomonic for glomerulonephritis, indicating that red blood cells originated from the glomerulus and became trapped in tubular casts.
The underlying mechanism involves inflammatory glomerular injury, leading to disruption of the glomerular basement membrane and activation of the renin-angiotensin-aldosterone system causing sodium and water retention.
Dysmorphic red blood cells (acanthocytes) on urinalysis strongly suggest a glomerular source of bleeding, distinguishing nephritic syndrome from lower urinary tract causes of hematuria.
Complement levels (C3, C4, CH50) are a key differentiator: low complement is seen in post-streptococcal GN, lupus nephritis, membranoproliferative GN, and cryoglobulinemia, while complement is normal in IgA nephropathy and anti-GBM disease.
Post-streptococcal glomerulonephritis is the classic pediatric nephritic syndrome, presenting 1–3 weeks after pharyngitis or 3–6 weeks after impetigo with low C3, elevated ASO titers, and "lumpy-bumpy" subepithelial immune deposits on electron microscopy.
IgA nephropathy (Berger disease) is the most common glomerulonephritis worldwide, presenting with episodic gross hematuria concurrent with upper respiratory infections (synpharyngitic) and mesangial IgA deposits on immunofluorescence.
Anti-GBM disease (Goodpasture syndrome) presents with nephritic syndrome plus pulmonary hemorrhage, caused by anti-type IV collagen antibodies, with linear IgG deposits on immunofluorescence and positive serum anti-GBM antibodies.
ANCA-associated vasculitides (granulomatosis with polyangiitis, microscopic polyangiitis) cause a pauci-immune glomerulonephritis with nephritic features, negative or minimal immunofluorescence staining, and positive serum c-ANCA or p-ANCA.
Rapidly progressive glomerulonephritis (RPGN) is the most severe nephritic presentation, defined by >50% loss of renal function within weeks, with crescents (proliferating parietal epithelial cells) on biopsy representing a nephrologic emergency requiring immediate treatment.