Nephritic Syndrome

Nephritic Syndrome – High‑Yield Study Guide for Medical Students

Definition

Nephritic syndrome is a clinical syndrome resulting from inflammatory injury of the glomeruli, leading to a classic constellation of findings:

• Hematuria (often macroscopic, with RBC casts)
• Variable proteinuria (usually < 3.5 g/day, sub‑nephrotic)
• Reduced GFR with rising serum creatinine
• Oliguria
• Hypertension (volume and RAAS mediated)
• Mild to moderate edema

It reflects an acute or subacute inflammatory glomerulonephritis, which can be primary (kidney‑limited) or secondary to systemic disease. A structured approach to glomerular disease helps categorize nephritic presentations, guide investigations, and initiate appropriate therapy early to prevent chronic kidney disease (CKD) progression.[6](https://europepmc.org/article/MED/41728366)

Epidemiology

Nephritic syndrome is a syndromic diagnosis, and its epidemiology depends on the underlying glomerular disease:

• Acute post‑streptococcal glomerulonephritis (APSGN) is a leading cause of acute nephritic syndrome in children worldwide, especially in low‑ and middle‑income regions.[2](https://pubmed.ncbi.nlm.nih.gov/40650562)
• IgA nephropathy (IgAN) is the most common primary glomerulonephritis globally and a frequent cause of recurrent macroscopic hematuria and nephritic presentations in young adults.[1](https://pubmed.ncbi.nlm.nih.gov/41126081/)
• Immunoglobulin A vasculitis (IgAV, Henoch–Schönlein) is a common small‑vessel vasculitis of childhood; renal involvement produces a nephritic picture.[4](https://pubmed.ncbi.nlm.nih.gov/38828518/)
• Membranoproliferative glomerulonephritis (MPGN) and C3 glomerulopathy are rare but important causes of chronic or relapsing nephritic syndrome in adolescents and adults.[7](https://europepmc.org/article/MED/41783430) [9](https://europepmc.org/article/MED/41767602)
• In adults, systemic diseases such as ANCA‑associated vasculitis and lupus nephritis are key causes of rapidly progressive nephritic presentations.[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)

Pathophysiology

The core mechanism in nephritic syndrome is immune‑mediated inflammation of the glomerular capillary wall, leading to disruption of the glomerular filtration barrier and a fall in GFR.

Immune Injury and Inflammation

• Immune complexes (circulating or in situ) or autoantibodies deposit in or target glomerular structures, triggering complement activation.
• Complement activation (classical, alternative or lectin pathway) generates C3a, C5a and the membrane attack complex, recruiting neutrophils and monocytes and causing endothelial injury.[7](https://europepmc.org/article/MED/41783430) [9](https://europepmc.org/article/MED/41767602)
• Endocapillary proliferation, influx of inflammatory cells, and swelling narrow the capillary lumen, leading to reduced GFR and oliguria.

Structural Consequences

• Capillary wall damage allows red blood cells and proteins to leak into Bowman space, producing hematuria, RBC casts, and proteinuria.
• Sodium and water retention from reduced GFR and RAAS activation lead to volume overload, causing hypertension and edema.
• In severe forms (e.g., ANCA vasculitis, anti‑GBM disease, severe lupus nephritis), crescent formation in Bowman space can cause rapidly progressive glomerulonephritis (RPGN) with rapid loss of kidney function.[6](https://europepmc.org/article/MED/41728366)

Etiologic Categories

Major etiologic groups that present with nephritic syndrome include:

• Post‑infectious GN (classically post‑streptococcal)
• IgA‑mediated disease: IgA nephropathy, IgA vasculitis (IgAV)[1](https://pubmed.ncbi.nlm.nih.gov/41126081/) [4](https://pubmed.ncbi.nlm.nih.gov/38828518/)
• Immune complex–mediated MPGN and C3 glomerulopathy[7](https://europepmc.org/article/MED/41783430) [9](https://europepmc.org/article/MED/41767602)
• Systemic autoimmune disease: systemic lupus erythematosus (lupus nephritis), ANCA‑associated vasculitis, anti‑GBM disease[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)

Clinical Presentation

Nephritic syndrome typically presents with an acute or subacute picture of glomerular injury. The exact presentation depends on the cause and rate of onset.

Core Features

• Hematuria
  • Cola‑colored or smoky urine; may be microscopic only.
  • Urinary sediment with dysmorphic RBCs and RBC casts (hallmark of glomerular bleeding).[6](https://europepmc.org/article/MED/41728366)
• Proteinuria
  • Usually sub‑nephrotic (< 3.5 g/day), but may reach nephrotic range in mixed nephritic–nephrotic pictures (e.g., lupus, MPGN).[9](https://europepmc.org/article/MED/41767602)
• Reduced GFR / AKI
  • Rising serum creatinine, oliguria, sometimes uremic symptoms if severe.
• Hypertension
  • Due to volume expansion and RAAS activation; may be severe in pediatric APSGN and vasculitis.[2](https://pubmed.ncbi.nlm.nih.gov/40650562)
• Edema
  • Periorbital (common in children), peripheral, and sometimes pulmonary edema.

Associated Systemic Features by Etiology

• Post‑streptococcal GN (APSGN) – occurs 1–3 weeks after streptococcal pharyngitis or impetigo; features include malaise, fever, edema, and gross hematuria.[2](https://pubmed.ncbi.nlm.nih.gov/40650562)
• IgA nephropathy – episodic gross hematuria within 24–48 h of upper respiratory or GI infection, commonly in young males.[1](https://pubmed.ncbi.nlm.nih.gov/41126081/)
• IgA vasculitis (IgAV) – tetrad of palpable purpura (usually lower limbs), arthralgia/arthritis, abdominal pain, and renal involvement (hematuria ± proteinuria).[4](https://pubmed.ncbi.nlm.nih.gov/38828518/)
• Lupus nephritis – systemic features (malar rash, oral ulcers, arthritis, serositis), cytopenias, and positive ANA/anti‑dsDNA.[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)
• ANCA‑associated vasculitis – constitutional symptoms, pulmonary hemorrhage, ENT disease, neuropathy, purpura, and rapidly progressive renal failure.[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)
• MPGN / C3 glomerulopathy – often insidious onset, mixed nephritic‑nephrotic syndrome, persistent hypocomplementemia, and sometimes association with chronic infections or dysregulated complement.[7](https://europepmc.org/article/MED/41783430) [8](https://europepmc.org/article/MED/41764449)

Diagnosis

Diagnosis of nephritic syndrome requires integration of clinical findings, laboratory tests, serologies, and often kidney biopsy. Early recognition of a nephritic picture is crucial to guide timely referral and prevent irreversible damage.[6](https://europepmc.org/article/MED/41728366)

Initial Laboratory Evaluation

• Urinalysis
  • Hematuria, dysmorphic RBCs, RBC casts.
  • Proteinuria (dipstick, spot protein/creatinine ratio or 24‑hour collection).
• Basic blood tests
  • Serum creatinine, BUN, electrolytes to assess kidney function.
  • CBC (anemia, leukocytosis, thrombocytopenia), CRP/ESR.
  • Liver function tests if relevant.
• Complement levels
  • C3, C4 to distinguish hypocomplementemic conditions (e.g., APSGN, MPGN, C3 glomerulopathy, lupus nephritis) from normocomplementemic causes (e.g., IgAN, ANCA vasculitis).[7](https://europepmc.org/article/MED/41783430) [9](https://europepmc.org/article/MED/41767602)

Etiology‑Focused Serologic Tests

• Post‑infectious GN
  • ASO titer, anti‑DNase B, throat culture, or skin culture in appropriate contexts.[2](https://pubmed.ncbi.nlm.nih.gov/40650562)
• Lupus nephritis
  • ANA, anti‑dsDNA, anti‑Sm, complement levels, antiphospholipid antibodies.[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)
• ANCA‑associated vasculitis
  • c‑ANCA (PR3), p‑ANCA (MPO) testing; look for systemic vasculitic features.[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)
• Anti‑GBM disease
  • Anti‑GBM antibodies, especially in pulmonary‑renal syndromes.
• MPGN / C3 glomerulopathy
  • Complement profile, testing for monoclonal gammopathy, chronic infections (HBV, HCV), and inherited complement abnormalities.[7](https://europepmc.org/article/MED/41783430) [9](https://europepmc.org/article/MED/41767602)

Imaging

• Renal ultrasound to assess kidney size, echogenicity, and exclude obstruction; usually shows normal or enlarged kidneys in acute nephritic processes.

Kidney Biopsy

Kidney biopsy is often indicated to precisely characterize the glomerular lesion, especially with rapidly progressive course, significant proteinuria, or unclear etiology.

• Light microscopy – identifies proliferative patterns (endocapillary proliferation, crescents, MPGN pattern).[9](https://europepmc.org/article/MED/41767602)
• Immunofluorescence – distinguishes immune‑complex deposition (granular IgG, IgA, C3) from pauci‑immune ANCA vasculitis or C3‑dominant deposition in C3 glomerulopathy.[7](https://europepmc.org/article/MED/41783430)
• Electron microscopy – localizes immune deposits (subepithelial “humps” in post‑infectious GN, mesangial IgA deposits in IgAN, dense deposits in C3 glomerulopathy).[1](https://pubmed.ncbi.nlm.nih.gov/41126081/) [7](https://europepmc.org/article/MED/41783430)

Management

Management of nephritic syndrome combines supportive therapy for AKI and volume overload with cause‑specific immunosuppressive or antimicrobial treatment. Early nephrology involvement is recommended in most cases.[6](https://europepmc.org/article/MED/41728366)

General Supportive Measures

• Blood pressure and volume control
  • Salt and fluid restriction.
  • Loop diuretics (e.g., furosemide) for edema and volume overload.
  • Antihypertensives; ACE inhibitors/ARBs are used cautiously in AKI but are beneficial chronically for proteinuria and BP control.
• Management of AKI
  • Adjust drug doses, avoid nephrotoxins (e.g., NSAIDs, iodinated contrast).
  • Monitor electrolytes; treat hyperkalemia and metabolic acidosis as required.
  • Renal replacement therapy for refractory volume overload, uremia, or severe electrolyte disturbance.
• Proteinuria and CKD risk reduction
  • Long‑term RAAS blockade, BP control, and lifestyle interventions to slow progression once acute inflammation is controlled.[6](https://europepmc.org/article/MED/41728366)

Etiology‑Specific Treatment

• Post‑streptococcal GN (APSGN)
  • Primarily supportive: BP and volume management; most children recover fully.
  • Penicillin or appropriate antibiotic if residual streptococcal infection is present.[2](https://pubmed.ncbi.nlm.nih.gov/40650562)
• IgA nephropathy / IgA vasculitis
  • Optimized BP control and RAAS blockade for proteinuric disease.
  • Short courses of glucocorticoids may be used in selected high‑risk IgAN or severe IgAV nephritis.[1](https://pubmed.ncbi.nlm.nih.gov/41126081/) [4](https://pubmed.ncbi.nlm.nih.gov/38828518/)
• Lupus nephritis
  • Treatment is class‑dependent (e.g., mycophenolate mofetil or cyclophosphamide plus glucocorticoids for proliferative classes, then maintenance with MMF or azathioprine).[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)
• ANCA‑associated vasculitis
  • High‑dose glucocorticoids plus rituximab or cyclophosphamide for induction, followed by maintenance immunosuppression (e.g., rituximab, azathioprine).[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)
• Anti‑GBM disease
  • Combination of high‑dose glucocorticoids, cyclophosphamide, and plasma exchange to remove circulating antibodies.
• MPGN and C3 glomerulopathy
  • Treat underlying cause (infections, monoclonal gammopathy).
  • Glucocorticoids and other immunosuppressants are used in immune‑complex MPGN.
  • Complement‑directed therapies (e.g., C5 inhibitors) are emerging for C3 glomerulopathy; evidence is evolving.[7](https://europepmc.org/article/MED/41783430) [9](https://europepmc.org/article/MED/41767602)

Key Clinical Pearls for Exams and Practice

• Think nephritic syndrome in any patient with acute hematuria, hypertension, and rising creatinine, especially with RBC casts on urinalysis.[6](https://europepmc.org/article/MED/41728366)
• APSGN is the classic child with periorbital edema, cola‑colored urine, hypertension, low C3, and recent streptococcal infection; prognosis is generally good.[2](https://pubmed.ncbi.nlm.nih.gov/40650562)
• IgA nephropathy vs APSGN: IgAN presents with hematuria during or within days of infection, normal complement; APSGN typically follows infection by 1–3 weeks and has low C3.[1](https://pubmed.ncbi.nlm.nih.gov/41126081/) [2](https://pubmed.ncbi.nlm.nih.gov/40650562)
• IgA vasculitis (IgAV) is essentially IgA nephropathy plus systemic small‑vessel vasculitis with palpable purpura, abdominal pain, and arthralgia.[4](https://pubmed.ncbi.nlm.nih.gov/38828518/)
• Hypocomplementemia suggests post‑infectious GN, lupus nephritis, MPGN, or C3 glomerulopathy; persistent hypocomplementemia with an MPGN pattern should raise suspicion for C3 glomerulopathy.[7](https://europepmc.org/article/MED/41783430) [8](https://europepmc.org/article/MED/41764449)
• Rapidly progressive oliguria with crescents on biopsy indicates RPGN, often due to ANCA vasculitis, anti‑GBM disease, or severe immune‑complex GN; urgent immunosuppression and often plasma exchange are required.[3](https://pubmed.ncbi.nlm.nih.gov/40213126/)
• Kidney biopsy is key for definitive diagnosis in most adult nephritic presentations and guides therapy and prognosis.[6](https://europepmc.org/article/MED/41728366)
• Long‑term follow‑up is essential; even after an apparently resolved acute episode, some patients progress to CKD or ESRD, especially those with MPGN, C3 glomerulopathy, or severe lupus nephritis.[7](https://europepmc.org/article/MED/41783430) [9](https://europepmc.org/article/MED/41767602)

Summary

Nephritic syndrome represents inflammatory glomerular injury with hematuria, variable proteinuria, AKI, hypertension, and edema. The most common causes include post‑infectious GN, IgA‑mediated disease, autoimmune nephritides (lupus, ANCA vasculitis, anti‑GBM), and MPGN/C3 glomerulopathy. A systematic clinical and serologic work‑up, complemented by kidney biopsy, is critical for accurate diagnosis and rational, etiology‑directed management.[1](https://pubmed.ncbi.nlm.nih.gov/41126081/) [2](https://pubmed.ncbi.nlm.nih.gov/40650562/) [6](https://europepmc.org/article/MED/41728366)