IgA nephropathy (Berger disease) is the most common primary glomerulonephritis worldwide. It most frequently affects males in the second to third decades of life. Clinical manifestations are usually triggered by upper respiratory tract or gastrointestinal infections and include gross hematuria and flank pain. In some cases, it may present as rapidly progressive glomerulonephritis (RPGN). Urinalysis of asymptomatic patients often shows persistent microhematuria and minor proteinuria, while more severe cases may manifest with recurrent episodes of nephritic syndrome. A kidney biopsy is indicated in patients with signs of severe or progressive disease to make a definitive diagnosis. Treatment consists of measures to slow the progression of the disease (e.g., ACE inhibitors) as well as immunosuppressive therapy in more severe cases. Even with the appropriate treatment, up to 50% of patients progress to end-stage renal disease within 20–25 years.
- Peak incidence: second to third decades of life 
- Sex: ♂ > ♀ (2:1) 
- Ethnicity: more common in the Asian population (worldwide) 
Epidemiological data refers to the US, unless otherwise specified.
- The cause is still not entirely understood.
- Most likely mechanism: an increased number of defective, circulating IgA antibodies are synthesized (often triggered by mucosal infections, i.e., upper respiratory tract and gastrointestinal infections) → IgA antibodies form immune complexes that deposit in the kidney → glomerulonephritis (type III hypersensitivity reaction) 
The course of the disease is highly variable and can manifest in the following forms:
- Recurring episodes of:
- Can progress to RPGN and/or nephrotic syndrome (< 10% of patients)
- Up to 50% of patients progress to end-stage renal disease within 20–25 years.
IgA nephropathy and Henoch-Schonlein purpura (HSP) are both IgA-mediated vasculitides triggered by a mucosal infection. HSP most commonly occurs in children < 10 years of age and affects multiple organ systems (palpable purpura, abdominal pain, arthralgia). IgA nephropathy is limited to the kidneys and typically affects adults.
Diagnosis is based on clinical presentation and laboratory results. In some cases, renal biopsy may be indicated to confirm the diagnosis.
- Serum IgA level is elevated in 50% of patients.
- Complement levels (e.g., C3 level) are generally normal. 
- Usually only indicated if there are signs of severe or progressive disease, including:
- Associated with low complement levels
- Typically occurs 10–20 days following an infection
- Lupus nephritis
- Membranoproliferative glomerulonephritis
The differential diagnoses listed here are not exhaustive.
- Patients with isolated hematuria
- Patients with proteinuria or hypertension: ACE inhibitors/angiotensin II receptor blockers
- For severe/rapidly progressive disease: glucocorticoids PLUS possibly cyclophosphamide/azathioprine