Nephritic vs nephrotic syndrome
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Nephritic vs Nephrotic Syndrome
Both are glomerular diseases, but they differ fundamentally in mechanism, clinical presentation, urine findings, and the diseases that cause them.
Core Concept: The Fundamental Difference
| Feature | Nephrotic | Nephritic |
|---|---|---|
| Mechanism | Loss of glomerular charge/size selectivity -> protein leak | Glomerular inflammation -> blood and protein leak |
| Process | Non-inflammatory | Inflammatory (proliferative GN) |
| Dominant finding | Massive proteinuria | Hematuria + active urinary sediment |
Nephrotic Syndrome
Definition: Proteinuria >3.5 g/day (nephrotic range), reflecting severe impairment of the glomerular filtration barrier.
Pathophysiology
Injury to podocytes (epithelial cells) disrupts the combined charge and size selectivity of the glomerular basement membrane, allowing large molecules like albumin to escape into urine. The loss of proteins drives all downstream complications. - Frameworks for Internal Medicine, p. 463
Clinical Features
- Edema - often severe, from periorbital puffiness to anasarca, ascites, and pleural effusions. Caused by hypoalbuminemia reducing oncotic pressure.
- Foamy urine (proteinuria)
- Hypertension
- Fatigue, dyspnea
- Muehrcke's lines (white transverse nail bands), eruptive xanthomata (rare)
Lab Findings
| Lab | Finding |
|---|---|
| Urine protein | >3.5 g/day |
| Urine sediment | Bland (oval fat bodies, lipid casts, fatty casts) |
| Serum albumin | <2.5 g/dL |
| Cholesterol | Usually >180 mg/dL (hyperlipidemia) |
| GFR | Usually preserved (except in MCD, HIV nephropathy, renal vein thrombosis) |
Why the Complications?
| Complication | Mechanism |
|---|---|
| Hypercoagulability / thromboembolism | Loss of antithrombin, proteins C and S in urine + increased fibrinogen production. Most common sites: renal veins, lower extremity veins. |
| Infections (cellulitis, peritonitis, pneumonia) | Loss of immunoglobulins and opsonins in urine |
| Hyperlipidemia | Compensatory hepatic lipoprotein synthesis when oncotic pressure falls |
Primary Causes (in order of prevalence in adults)
- Focal Segmental Glomerulosclerosis (FSGS) - most common overall; especially common in Black patients (~50% of cases). Higher risk of thromboembolism vs. other causes.
- Membranous Nephropathy - most common cause in White adults; can be primary (anti-PLA2R antibodies) or secondary (SLE, hepatitis B, penicillamine, malignancy - e.g., colon cancer)
- Minimal Change Disease (MCD) - causes 70-90% of nephrotic syndrome in children, only 10-15% in adults. Normal biopsy on light microscopy; electron microscopy shows podocyte foot process effacement. First-line: systemic glucocorticoids (>80% remission rate)
- Membranoproliferative GN (MPGN)
- Diabetic nephropathy (most common secondary cause)
- Amyloidosis
- Harrison's Principles of Internal Medicine 22E, p. 1310-1318; Goldman-Cecil Medicine, p. 1175
Nephritic Syndrome
Definition: A syndrome of glomerular inflammation (glomerulonephritis) characterized by hematuria, active urinary sediment, variable proteinuria, hypertension, and azotemia. - Robbins Pathologic Basis of Disease
Pathophysiology
Proliferation of glomerular cells + infiltration of inflammatory leukocytes damages capillary walls. This allows blood cells into urine (hematuria) and severely reduces GFR. Reduced GFR leads to fluid retention (oliguria, edema, hypertension), while ischemic kidneys release renin, worsening hypertension. - Robbins, p. 3054-3064
Clinical Features
- Hematuria (gross or microscopic; tea/cola-colored urine)
- Oliguria
- Hypertension (fluid retention + renin release)
- Edema (less severe than nephrotic)
- Azotemia (elevated BUN/creatinine)
Lab Findings
| Lab | Finding |
|---|---|
| Urine sediment | Active - dysmorphic RBCs, RBC casts (pathognomonic), WBC casts |
| Urine protein | Mild to moderate (usually <3.5 g/day; sub-nephrotic) |
| Serum creatinine | Elevated (reduced GFR) |
| Complement | Low in some causes (post-streptococcal, lupus, MPGN) |
The hallmark is dysmorphic RBCs and RBC casts. Their absence does not exclude nephritic syndrome. - Goldman-Cecil Medicine, p. 1175
Primary Causes
| Cause | Key Features |
|---|---|
| Post-infectious GN (esp. post-streptococcal) | 1-4 weeks after pharyngitis or impetigo; children 6-10 years; immune complex deposition |
| IgA Nephropathy (Berger disease) | Most common primary GN worldwide; hematuria within 1-2 days of URI |
| Rapidly Progressive (Crescentic) GN | ANCA-associated (GPA, MPA, EGPA), anti-GBM disease (Goodpasture's), immune complex-mediated |
| Lupus Nephritis (Class III/IV) | Immune complex deposition |
| ANCA-associated vasculitis | Pauci-immune; ANCA positive |
| Anti-GBM disease | Linear IgG on IF; pulmonary hemorrhage if Goodpasture's |
- Goldman-Cecil Medicine, p. 1175; Robbins, p. 3054
Side-by-Side Comparison Table
| Feature | Nephrotic | Nephritic |
|---|---|---|
| Mechanism | Podocyte/barrier injury | Glomerular inflammation |
| Proteinuria | >3.5 g/day (massive) | <3.5 g/day (mild-moderate) |
| Hematuria | Absent or minimal | Present (dysmorphic RBCs) |
| RBC casts | No | Yes (pathognomonic) |
| Urine sediment | Bland (fatty casts) | Active (RBC casts, WBC casts) |
| Edema | Severe (anasarca) | Mild-moderate |
| Hypoalbuminemia | Yes | Mild/absent |
| Hyperlipidemia | Yes | No |
| Hypertension | Can occur | Prominent |
| Azotemia/Oliguria | Uncommon (initially) | Common |
| GFR | Usually preserved | Usually reduced |
| Serum complement | Normal | Low (in some: post-strep, SLE, MPGN) |
| Hypercoagulability | Yes (renal vein thrombosis risk) | No |
| Infection risk | Increased | Increased (different mechanism) |
Memory Aids
- NephROTic = ROTten protein leak = lots of protein (the "O" for proteinuria)
- NephRITic = RITch blood in urine = hematuria + inflammation (the "I" for inflammation)
- Nephrotic: think "holes in the filter" (protein pours out, blood stays)
- Nephritic: think "filter is on fire" (inflammation blows out blood cells)
Overlap
Some diseases can present with features of both syndromes:
- MPGN and IgA nephropathy can each cause either presentation
- Lupus nephritis (especially class IV) can have both heavy proteinuria and active sediment
- The two syndromes are not mutually exclusive - Frameworks for Internal Medicine, p. 463
Sources: Robbins Pathologic Basis of Disease; Harrison's Principles of Internal Medicine 22E; Goldman-Cecil Medicine International Edition; Frameworks for Internal Medicine
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