Bit · Renal
Nephritic vs Nephrotic syndromes
Two glomerular syndromes that share urine findings but split on whether the glomerular barrier is broken (nephritic) or simply leaky (nephrotic). The pivot is RBC casts vs proteinuria magnitude.
Mechanism
Both reflect glomerular injury, but the mechanism differs:
- Nephritic syndrome — glomerular inflammation disrupts the basement membrane. RBCs escape into the urine → hematuria with RBC casts and dysmorphic RBCs. Inflammation reduces GFR → oliguria, azotemia, HTN, mild edema. Proteinuria is sub-nephrotic (<3.5 g/day).
- Nephrotic syndrome — non-inflammatory damage to podocytes / GBM increases permeability. Massive protein loss → proteinuria >3.5 g/day, hypoalbuminemia, edema, hyperlipidemia, lipiduria (fatty casts, 'oval fat bodies', Maltese cross under polarized light). Also a hypercoagulable state from urinary loss of antithrombin III.
Differentiator Table
| Nephritic | Nephrotic | |
| Mechanism | Glomerular inflammation, GBM disruption | Podocyte / GBM permeability without inflammation |
| Proteinuria | < 3.5 g/day | > 3.5 g/day |
| Hematuria | Prominent (RBC casts, dysmorphic RBCs) | Mild or absent |
| BP | Hypertension common | Often normal early |
| Edema | Mild, periorbital | Severe, generalised (frothy urine) |
| Lipids | Normal | Hyperlipidemia, lipiduria, oval fat bodies |
| Hypercoagulability | No | Yes (loss of antithrombin III) — renal vein thrombosis |
| Classic causes | Post-strep GN, IgA nephropathy (Berger), RPGN (Goodpasture, GPA, anti-GBM, immune complex), Alport, membranoproliferative GN | Minimal change disease (kids), FSGS (adults, HIV, heroin, sickle cell), membranous nephropathy (adults, HBV, SLE), diabetic nephropathy, amyloidosis |
| Light/EM | 'Lumpy-bumpy' granular IF (immune complex) or linear IF (anti-GBM) | Minimal change: foot process effacement on EM only; membranous: subepithelial 'spike-and-dome' |
The Pivot
Two findings split it cleanly:
- RBC casts on urinalysis? → nephritic.
- Proteinuria > 3.5 g/day + hypoalbuminemia + edema? → nephrotic.
Then ask the cause. Nephritic patterns: child after strep throat → post-strep GN; gross hematuria after URI → IgA nephropathy; rapidly progressive with crescents → RPGN. Nephrotic patterns: child with sudden edema → minimal change; adult with insidious edema → FSGS or membranous; long-standing diabetes → diabetic nephropathy.
NBME-Style Stem
A 6-year-old boy develops periorbital edema and dark, cola-coloured urine 2 weeks after a sore throat. Blood pressure is 142/88 mm Hg. Urinalysis shows 3+ blood, 1+ protein, and red blood cell casts. Serum creatinine is 1.2 mg/dL. Complement C3 is decreased; C4 is normal. Which of the following is the most likely diagnosis?
Concept Anchor
Nephritic syndromes are an attack on the glomerular barrier — RBCs leak through breaches and form casts in the tubule. Nephrotic syndromes are a failure of selectivity in an intact-looking barrier — protein floods out without inflammation.