Most common primary glomerulonephritis; mesangial IgA deposits with synpharyngitic hematuria.
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Risk factors Family history of IgA nephropathy Asian or white ethnicity Mucosal infections (URIs, GI) — trigger flares Celiac disease, IBD, cirrhosis (secondary IgA deposition) Henoch-Schönlein purpura (IgA vasculitis) — systemic form Pathophysiology Galactose-deficient IgA1 (Gd-IgA1) is recognized by anti-glycan autoantibodies, forming circulating immune complexes that deposit in the mesangium. Mesangial cell proliferation, complement activation (alternative pathway), and cytokine release drive injury. Progressive disease causes glomerulosclerosis and tubulointerstitial fibrosis.
Clinical presentation Symptoms Gross hematuria within 1-3 days of URI, GI infection, or vigorous exercise (synpharyngitic) Asymptomatic microscopic hematuria (most common presentation) Flank pain during gross hematuria episodes Edema and hypertension if nephrotic-range proteinuria or significant impairment Signs / physical exam Often normal physical exam Hypertension (more common with progression) Edema if heavy proteinuria Skin/joint findings if IgA vasculitis variant Classic findings Recurrent episodes of cola-colored urine within 24-72 hours of a URI = synpharyngitic hematuria of IgA nephropathy.
Differential diagnosis Post-streptococcal GN — Hematuria 1-3 weeks after strep infection (not same-day); low C3; positive ASO; usually self-limitedThin basement membrane disease — Benign familial hematuria; isolated microhematuria; thin GBM on EM; preserved functionAlport syndrome — X-linked; hematuria + sensorineural hearing loss + ocular findings; type IV collagen mutationHenoch-Schönlein purpura (IgA vasculitis) — Same pathology + palpable purpura, arthralgia, abdominal pain; usually in childrenLupus nephritis — Systemic SLE features; full-house IF pattern (vs IgA-dominant)Urinary tract source of hematuria — Eumorphic RBCs, no casts, no proteinuria; cystoscopy and urology workupDiagnostic workup Diagnostic criteria Definitive diagnosis requires kidney biopsy showing dominant or co-dominant mesangial IgA deposition on immunofluorescence with mesangial proliferation on light microscopy. Oxford MEST-C score (mesangial hypercellularity, endocapillary, segmental sclerosis, tubular atrophy, crescents) prognosticates.
Labs Urinalysis with microscopy — hematuria with dysmorphic RBCs, sometimes RBC casts; mild proteinuria Spot UPCR — proteinuria quantification (>1 g/day = poor prognosis) BMP with creatinine and eGFR Serum IgA elevated in ~50% (nonspecific, not diagnostic) Normal complement (helps distinguish from post-strep, lupus, MPGN) Negative ANA, ANCA, anti-GBM (to exclude alternatives) Imaging Renal ultrasound to assess size and exclude obstruction in presence of gross hematuria Diagnostic algorithm Feature IgA Nephropathy Post-Strep GN Timing after infection 1-3 days (synpharyngitic) 1-3 weeks (latent) Complement (C3) Normal Low Serology Elevated IgA (~50%) ASO, anti-DNase B positive Course Chronic, relapsing Self-limited (typically) Population Young adults, Asian/white Children, post-strep pharyngitis or impetigo Biopsy IF Mesangial IgA Granular IgG/C3, subepithelial 'humps' Long-term prognosis 20-40% ESRD over 20 yr Excellent in children, worse in adults
Distinguishing IgA nephropathy from post-streptococcal GN — timing, complement, and serology. Treatment First-line BP control with ACEi (lisinopril, ramipril) or ARB (losartan, valsartan) — first-line; titrate to maximally tolerated dose SGLT2 inhibitor — dapagliflozin or empagliflozin — added for proteinuria reduction and renal protection (KDIGO 2024) Target proteinuria <0.5-1 g/day; BP <120/80 Lifestyle: smoking cessation, sodium restriction, weight management Cardiovascular risk reduction: statin if indicated Second-line / adjunct Sparsentan (dual endothelin/angiotensin receptor antagonist) — for proteinuria >1 g/day despite RAAS blockade Targeted-release budesonide (Nefecon) — gut-restricted glucocorticoid for high-risk patients with persistent proteinuria Systemic glucocorticoids — controversial; consider in rapidly progressive disease (KDIGO suggests selective use) Crescentic IgA nephropathy: cyclophosphamide + steroids ± plasma exchange Tonsillectomy: variable evidence, more common in Asian practice RRT/transplant for ESRD — IgA can recur in allograft (~30%) Complications Progression to CKD/ESRD in 20-40% over 20 years Rapidly progressive (crescentic) GN — rare but severe Acute kidney injury from gross hematuria episodes (tubular obstruction by RBC casts) Hypertensive complications Recurrence post-transplant PANCE pearls Synpharyngitic hematuria (within 1-3 days of URI) = IgA. Post-streptococcal GN takes 1-3 weeks. Normal complement levels distinguish IgA from post-strep, lupus, and MPGN. MEST-C score guides prognosis: M1, E1, S1, T1-2, C1-2 each carry worse outcome. IgA vasculitis (Henoch-Schönlein purpura) is the systemic form: same renal pathology + palpable purpura, arthritis, abdominal pain. Persistent proteinuria >1 g/day is the strongest predictor of progression. References KDIGO 2021/2024 — KDIGO 2021 Guideline for Management of Glomerular Diseases; 2024 IgA Nephropathy UpdatePROTECT — Sparsentan in IgA Nephropathy (Heerspink et al., Lancet 2023)NefIgArd — Targeted-release Budesonide for IgA Nephropathy (Barratt et al., Lancet 2023)Oxford Classification — Oxford Classification of IgA Nephropathy: 2016 Update (Trimarchi et al., Kidney Int 2017)
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