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Summary Table

Category	Detail
Risk Factors	Young males (10-30 years old), Asian or Caucasian descent, often preceded by upper respiratory infection or GI illness
Etiology	Mesangial deposition of IgA immune complexes due to abnormally glycosylated IgA1
Patient Presentation	Episodic gross hematuria (cola/tea-colored urine) occurring 1-2 days after an upper respiratory tract infection ("synpharyngitic hematuria")
Classic Physical Exam	Often unremarkable; mild hypertension may be present; no edema in early disease
Key Diagnostic Results	Urinalysis: dysmorphic RBCs, RBC casts; serum IgA elevated in ~50%; renal biopsy shows mesangial IgA deposits on immunofluorescence
Management	Mild: ACE inhibitors or ARBs for proteinuria control. Severe/progressive: corticosteroids. ESRD: dialysis or transplantation
Keywords	"Gross hematuria after URI," "synpharyngitic," "mesangial IgA deposits," "young male with recurrent hematuria," "1-2 days after pharyngitis"

1. Pathophysiology

IgA nephropathy is the most common primary glomerulonephritis worldwide. The disease begins with a defect in the O-glycosylation of the IgA1 molecule at its hinge region. This produces what is known as galactose-deficient IgA1 (Gd-IgA1). Under normal circumstances, IgA1 is cleared efficiently from circulation. However, when the molecule is aberrantly glycosylated, the immune system recognizes these exposed N-acetylgalactosamine residues as foreign, triggering the production of anti-glycan IgG and IgA autoantibodies. These autoantibodies bind to Gd-IgA1 and form circulating immune complexes.

These immune complexes are too large to be cleared by normal hepatic mechanisms but small enough to pass through the glomerular circulation, where they become trapped in the mesangium. Once deposited, they activate the complement system via the alternative and lectin pathways (notably, C3 is deposited but C1q is typically absent, distinguishing this from lupus nephritis). Complement activation and direct mesangial cell stimulation trigger a local inflammatory cascade: mesangial cell proliferation, extracellular matrix expansion, and the release of cytokines and growth factors.

This mesangial inflammation is why the patient develops hematuria. Inflammatory damage to the glomerular basement membrane allows red blood cells to squeeze through, becoming dysmorphic in the process. Red blood cell casts form within the tubules, confirming that the bleeding originates from the glomerulus rather than from the lower urinary tract. The hallmark clinical feature is the timing of hematuria relative to infection: it occurs within 1-2 days of an upper respiratory or gastrointestinal illness (synpharyngitic), because mucosal infection stimulates a rapid surge in circulating IgA, which immediately worsens immune complex deposition.

Proteinuria develops as the disease progresses and indicates more severe podocyte injury and glomerular scarring. Persistent proteinuria above 1 g/day is one of the strongest predictors of progression to chronic kidney disease and eventual end-stage renal disease.

2. Classification and Clinical Manifestation

Clinical Presentation

Pattern	Description	Frequency
Episodic gross hematuria	Recurrent episodes of visible (cola-colored) hematuria within 1-2 days of mucosal infection; resolves spontaneously within days	Most common (~40-50%)
Persistent microscopic hematuria	Asymptomatic microscopic hematuria with or without mild proteinuria found incidentally on urinalysis	~30-40%
Nephrotic syndrome	Heavy proteinuria (>3.5 g/day), hypoalbuminemia, edema, hyperlipidemia	Uncommon (~5%)
Rapidly progressive (crescentic) GN	Acute renal failure with oliguria, rising creatinine, crescents on biopsy	Rare but serious
Chronic renal insufficiency	Insidious decline in GFR, hypertension, and progressive proteinuria discovered late	Variable

Oxford Classification (MEST-C Score) for Histopathology

This scoring system is used on renal biopsy to predict prognosis.

Component	Feature Assessed	Scoring
M	Mesangial hypercellularity	M0 (<50% of glomeruli) vs. M1 (>50%)
E	Endocapillary hypercellularity	E0 (absent) vs. E1 (present)
S	Segmental sclerosis	S0 (absent) vs. S1 (present)
T	Tubular atrophy / interstitial fibrosis	T0 (0-25%), T1 (26-50%), T2 (>50%)
C	Crescents	C0 (absent), C1 (<25% of glomeruli), C2 (>25%)

Higher scores (particularly T and C) indicate worse renal prognosis.

3. Diagnostic Workup

Test	Role	Expected Findings
Urinalysis with microscopy	Best initial test	Dysmorphic RBCs, RBC casts, variable proteinuria
Serum IgA level	Supportive (not diagnostic)	Elevated in ~50% of cases; normal level does not exclude diagnosis
Serum complement (C3, C4)	Differentiation from other GN	Normal (distinguishes from PSGN, lupus, MPGN)
24-hour urine protein or UPCR	Prognosis and treatment guidance	Quantifies proteinuria; >1 g/day indicates higher risk of progression
Serum creatinine and eGFR	Baseline renal function	May be normal early; elevated in progressive disease
Renal biopsy	Gold standard / most accurate test	Light microscopy: mesangial proliferation. Immunofluorescence: granular mesangial IgA deposits. Electron microscopy: electron-dense mesangial deposits

Diagnostic Reasoning

When a young male presents with episodic gross hematuria that coincides with or follows within 1-2 days of an upper respiratory infection, the clinical suspicion for IgA nephropathy should be high. The best initial test is a urinalysis with microscopy. The presence of dysmorphic red blood cells and RBC casts confirms a glomerular source of bleeding and immediately narrows the differential to glomerulonephritis.

The next step is to check serum IgA levels, which will be elevated in roughly half of patients. However, a normal IgA level does not rule out the disease, so this test is supportive rather than definitive. Crucially, you should also check serum complement levels (C3 and C4). In IgA nephropathy, complement levels are normal. This is a high-yield discriminator: if C3 is low, you should be thinking about post-streptococcal glomerulonephritis (PSGN), lupus nephritis, or membranoproliferative glomerulonephritis instead.

Quantifying proteinuria with a 24-hour urine collection or urine protein-to-creatinine ratio (UPCR) is essential for risk stratification. Proteinuria exceeding 1 g/day is associated with progressive renal decline and triggers more aggressive treatment.

The most accurate (confirmatory) test is a renal biopsy. On light microscopy, you will see mesangial proliferation and matrix expansion. On immunofluorescence, the pathognomonic finding is granular IgA deposition in the mesangium, often accompanied by C3 co-deposition. Importantly, C1q staining is absent or minimal, which distinguishes this from lupus nephritis (where "full house" staining with IgG, IgA, IgM, C3, and C1q is characteristic). On electron microscopy, electron-dense deposits are seen within the mesangium.

One important note: not every patient with suspected IgA nephropathy requires a biopsy. Biopsy is indicated when there is diagnostic uncertainty, persistent proteinuria above 0.5-1 g/day, worsening renal function, or when the result would change management.

4. Management and Treatment

Clinical Scenario	Treatment	Details
All patients with proteinuria	ACE inhibitor (e.g., enalapril, ramipril) or ARB (e.g., losartan, valsartan)	First-line for renoprotection; target proteinuria <1 g/day and BP <130/80 mmHg
Lifestyle	Dietary sodium restriction, smoking cessation	Supportive in all patients
Proteinuria >1 g/day despite 3-6 months of optimized ACEi/ARB	Add corticosteroids	Prednisone 0.5-1 mg/kg/day for 2 months, then taper over 4-6 months (total ~6 months)
Rapidly progressive / crescentic disease	Pulse IV methylprednisolone + cyclophosphamide or mycophenolate mofetil	Aggressive immunosuppression for severe crescentic GN
Isolated hematuria, no proteinuria, normal GFR	Observation and monitoring	No pharmacologic treatment needed; follow UA, proteinuria, and creatinine every 6-12 months
End-stage renal disease	Dialysis or kidney transplantation	IgA nephropathy can recur in the transplanted kidney (~50% histologic recurrence, though graft loss from recurrence is less common)
Fish oil (omega-3 fatty acids)	Controversial / optional	Some guidelines suggest a trial (4 g/day) for persistent proteinuria; evidence is mixed

Step 1: Supportive and renoprotective therapy. Every patient with proteinuria, regardless of severity, should be started on an ACE inhibitor or ARB. These agents reduce intraglomerular pressure and proteinuria, which slows progression. The target is to reduce proteinuria below 1 g/day and maintain blood pressure below 130/80 mmHg. Common regimens include ramipril 5-10 mg/day or losartan 50-100 mg/day, titrated to effect. These drugs are contraindicated in pregnancy (teratogenic) and in bilateral renal artery stenosis (risk of acute kidney injury from loss of efferent arteriolar tone).

Step 2: Reassess after 3-6 months. If proteinuria remains above 1 g/day despite maximally tolerated ACEi/ARB therapy, the next best step is to add corticosteroids. The typical regimen is oral prednisone at 0.5-1 mg/kg/day (maximum ~60 mg) for 2 months, followed by a gradual taper over 4-6 months. The TESTING trial (2022) showed that methylprednisolone reduced proteinuria and slowed eGFR decline, though with increased infection risk, reinforcing that the decision to use steroids must be balanced against side effects.

Step 3: Severe or rapidly progressive disease. If the patient presents with crescentic glomerulonephritis (rapidly rising creatinine, crescents on biopsy), this is treated as a renal emergency. Pulse IV methylprednisolone (500-1000 mg daily for 3 days) followed by oral prednisone plus cyclophosphamide or mycophenolate mofetil is used to halt the inflammatory damage.

Step 4: ESRD management. Patients who progress to end-stage renal disease require renal replacement therapy. Kidney transplantation is the preferred option, though patients should be counseled that histologic recurrence in the allograft occurs in roughly 50% of cases within 10 years. Clinically significant graft loss from recurrence, however, is lower (around 10-15%).

A newer agent worth mentioning is sparsentan, a dual endothelin and angiotensin receptor antagonist that has shown promise in reducing proteinuria in IgA nephropathy in the PROTECT trial and has received regulatory approval for this indication.

5. Differential Diagnosis and Distractors

Differential	Why It Looks Similar	Key Discriminator
Post-streptococcal GN (PSGN)	Both present with hematuria after pharyngitis in young patients	Timing: PSGN occurs 1-3 weeks after pharyngitis (latent period); IgA nephropathy occurs within 1-2 days. PSGN has low C3, elevated ASO/anti-DNase B, and subepithelial "humps" on EM
Alport syndrome	Recurrent hematuria in a young male	Alport is hereditary (X-linked most common); look for sensorineural hearing loss and ocular abnormalities (anterior lenticonus). Biopsy shows GBM splitting/lamellation ("basket-weave"), not IgA deposits
Thin basement membrane disease (benign familial hematuria)	Persistent microscopic hematuria, young patient, no proteinuria	Benign course with no progression; biopsy shows diffusely thin GBM without immune deposits; no RBC casts and no proteinuria
Lupus nephritis	Can have mesangial IgA deposition and hematuria	Lupus has systemic features (rash, arthritis, serositis), positive ANA/anti-dsDNA, low C3/C4, and "full house" immunofluorescence (IgG, IgA, IgM, C3, C1q)
Henoch-Schonlein Purpura (IgA vasculitis)	Same IgA-mediated mechanism; identical biopsy findings on renal tissue	HSP is a systemic vasculitis with palpable purpura on buttocks/legs, abdominal pain, arthralgia, and skin biopsy showing leukocytoclastic vasculitis with IgA. IgA nephropathy is renal-limited
Membranoproliferative GN (MPGN)	Hematuria with proteinuria and possible nephritic features	MPGN has low C3, "tram-track" appearance on GBM on light microscopy, and subendothelial deposits

6. Traps and High-Yield Pearls

The single most common way students get IgA nephropathy questions wrong is by confusing it with post-streptococcal glomerulonephritis. Both diseases present with hematuria following a pharyngitis episode, and both affect young patients. The critical discriminator is timing. If the vignette says the hematuria appeared "2 days after a sore throat," that is synpharyngitic hematuria and points to IgA nephropathy. If it says "2 weeks after a sore throat," that is the latent period characteristic of PSGN. Another giveaway: complement levels. IgA nephropathy has normal complement, while PSGN has low C3.

A second common trap is confusing IgA nephropathy with Henoch-Schonlein purpura (IgA vasculitis). The renal pathology is virtually identical, so the biopsy alone cannot distinguish the two. The distinction is purely clinical: HSP is a systemic disease with purpura, abdominal pain, and arthralgia, while IgA nephropathy is confined to the kidneys. If the vignette mentions any extrarenal IgA-related symptoms, you are dealing with HSP, not isolated IgA nephropathy.

A third pearl: the vignette may describe a patient with "persistently elevated serum IgA." Do not fall into the trap of thinking this confirms the diagnosis. Serum IgA is elevated in only about half of patients, and an elevated IgA is neither sensitive nor confirmatory. The gold standard remains renal biopsy with immunofluorescence showing mesangial IgA.

Finally, remember the prognostic indicators that suggest the disease will progress to chronic kidney disease: sustained proteinuria above 1 g/day, hypertension, elevated creatinine at presentation, and severe histologic findings on biopsy (high T and C scores on the Oxford classification). These are the patients who need aggressive treatment beyond ACEi/ARB alone. The core competency being tested is the ability to recognize the classic synpharyngitic presentation, distinguish it from PSGN by timing and complement levels, and sequence the workup from urinalysis to biopsy confirmation.

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