Nephritic syndrome shows up on exams the way it shows up in real life: sudden hematuria + hypertension after something inflammatory hits the glomerulus. If you can rapidly decide IgA nephropathy vs post-strep GN, you’ll pick up easy points—especially when the stem tries to distract you with edema, proteinuria, or “cola-colored urine.”
Nephritic syndrome: the “one-liner” you should memorize
Nephritic syndrome = inflammatory glomerular injury → RBCs leak (hematuria + RBC casts) + decreased GFR (oliguria, azotemia) + salt/water retention (HTN, mild edema).
Classic high-yield features
- Hematuria (often tea/cola-colored)
- RBC casts (hallmark of glomerular bleeding)
- Hypertension
- Oliguria
- Azotemia (↑ BUN/Cr)
- Proteinuria: usually subnephrotic (can be variable)
Visual mnemonic: “The Angry Filter”
Picture the glomerulus as a coffee filter:
- Nephritic = angry, inflamed filter
- It lets RBCs through (→ hematuria, RBC casts)
- It filters less overall (→ ↓ GFR → oliguria, azotemia)
- It holds onto salt/water (→ HTN, edema)
Key contrast to nephrotic: nephrotic is a “leaky” filter (protein loss), nephritic is an “inflamed” filter (blood + reduced filtration).
Quick triage: Is it IgA or post-strep?
The fastest decision rule (timing is everything)
- IgA nephropathy: hematuria within days of URI/GI infection (“synpharyngitic”)
- Post-strep GN: hematuria 1–3 weeks after strep throat or 3–6 weeks after impetigo
Side-by-side cheat sheet (exam-grade)
| Feature | IgA nephropathy (Berger) | Post-streptococcal GN (PSGN) |
|---|---|---|
| Typical age | Children/young adults | Children (classic), can occur in adults |
| Trigger timing | Within days of URI/GI infection (synpharyngitic) | Delayed: 1–3 wks after pharyngitis, 3–6 wks after impetigo |
| Pathogenesis | IgA immune complex deposition (often galactose-deficient IgA1) | Immune complex deposition after nephritogenic GAS strains |
| Complement levels | Usually normal (Step-style rule) | Low C3 (hypocomplementemia) |
| LM | Mesangial proliferation | Hypercellular glomeruli (endocapillary proliferation) |
| IF | Mesangial IgA (± C3) | “Starry sky” granular deposits (IgG, IgM, C3) |
| EM | Mesangial deposits | Subepithelial humps |
| Key clinical clue | Episodic gross hematuria after colds; can be recurrent | Cola urine + periorbital edema + HTN after strep infection |
| Prognosis | Variable; can progress to CKD | Kids often recover; adults more likely persistent renal dysfunction |
IgA nephropathy: high-yield bullets
The classic stem
- Young person gets a URI, then gross hematuria within 1–2 days
- May have recurrent episodes
- Mild proteinuria, HTN possible
Associations to remember
- IgA vasculitis (Henoch-Schönlein purpura): palpable purpura, abdominal pain, arthralgias + renal IgA
- Celiac disease and cirrhosis are commonly tested associations
Biopsy “must-know”
- IF: mesangial IgA
- LM: mesangial proliferation
Post-strep GN: high-yield bullets
The classic stem
- Child had strep throat a couple weeks ago (or impetigo weeks ago)
- Now: cola-colored urine, periorbital edema, hypertension
- Oliguria and elevated creatinine possible
Labs that seal the deal
- Low C3 (and total complement)
- Evidence of prior GAS infection:
- ↑ ASO (more with pharyngitis)
- ↑ anti–DNase B (especially helpful for impetigo)
Biopsy “must-know”
- IF: granular (“lumpy-bumpy”) deposition of IgG, IgM, C3
- EM: subepithelial humps
“RBC casts” = nephritic until proven otherwise
When you see:
- RBC casts
- Dysmorphic RBCs
- Hematuria + HTN
…think glomerular inflammation (nephritic picture). This is a high-yield discriminator from lower-tract causes of hematuria (stones, cystitis), which do not produce RBC casts.
Mini table: nephritic vs nephrotic (for 10-second test-taking)
| Feature | Nephritic | Nephrotic |
|---|---|---|
| Primary problem | Inflammation → RBC leakage + ↓ GFR | Podocyte injury → protein leakage |
| Urine | Hematuria, RBC casts | Proteinuria > 3.5 g/day, fatty casts/oval fat bodies |
| Edema | Mild–moderate | Often marked |
| Lipids | Usually not major | Hyperlipidemia |
| Key complications | HTN, AKI | Thrombosis, infections |
USMLE-style “one-liners” (memorize these)
- IgA nephropathy: “Hematuria within days of URI = synpharyngitic IgA in mesangium.”
- Post-strep GN: “Hematuria weeks after strep + low C3 + subepithelial humps.”
Common pitfalls (that cost points)
- Mixing up timing:
- Days after infection → IgA
- Weeks after infection → PSGN
- Forgetting complement: low C3 strongly supports PSGN (and other complement-consuming GN), whereas IgA is usually normal complement.
- Calling it nephrotic because there’s edema: nephritic syndromes can cause edema via salt/water retention from reduced GFR—but hematuria + RBC casts is the giveaway.
Super-fast practice stems (self-check)
- 20-year-old with gross hematuria 1 day after sore throat → likely IgA nephropathy
- 7-year-old with cola urine + periorbital edema 2 weeks after strep throat, low C3 → likely PSGN