A 32-year-old man complains of recurrent hematuria since his youth. The hematuria typically occurs following upper respiratory tract infections. Vital signs are normal. Urinalysis shows proteinuria, hematuria, and a few red blood cell casts. Laboratory studies disclose normal levels of BUN and creatinine. The ANA and ANCA tests are negative. Which of the following is the most likely diagnosis?

Berger disease is the most common form of glomerulonephritis in adults. Deposition of IgA-dominant immune complexes is the cause of the nephropathy, but the constituent antigens and the mechanism of accumulation have not been determined. Exacerbations of IgA nephropathy are often initiated by infections of the respiratory or gastrointestinal tracts. The diagnostic finding on renal biopsy is intense mesangial staining for IgA, which is almost always accompanied by staining for C3. IgA nephropathy manifests a continuum of glomerulopathies, ranging from no discernible light microscopic changes to chronic sclerosing glomerulonephritis. Patients frequently present with hematuria and proteinuria, and 20% of patients develop renal failure after 10 years. Neither amyloid nephropathy (choice A) nor membranous nephropathy (choice D) features RBC casts. Hereditary nephritis (Alport syndrome; choice C) reflects abnormal type IV collagen in the glomerular basement membrane. Hematuria is present early in life; proteinuria, progressive renal failure, and hypertension develop later in the course of the disease. Wegener granulomatosis (choice E) is usually positive for ANCA.Diagnosis: Berger disease, IgA nephropathy