**Core Concept**
The patient's presentation of recurrent hematuria, especially in association with upper respiratory tract infections, suggests a condition involving the kidneys and possibly an immune response.

**Why the Correct Answer is Right**
The presence of hematuria, proteinuria, and red blood cell casts in the urine, along with the absence of kidney dysfunction (normal BUN and creatinine levels), points towards a glomerulonephritis. The patient's symptoms and laboratory findings are consistent with IgA nephropathy, also known as Berger's disease. IgA nephropathy is characterized by the deposition of IgA antibodies in the glomeruli, leading to inflammation and damage. The disease often presents with recurrent episodes of gross hematuria, particularly following upper respiratory tract infections, which trigger the deposition of IgA antibodies in the kidneys.

**Why Each Wrong Option is Incorrect**

**Option A:** Focal segmental glomerulosclerosis (FSGS) is a cause of nephrotic syndrome, characterized by heavy proteinuria and often normal hematuria. However, FSGS does not typically present with recurrent episodes of gross hematuria following upper respiratory tract infections.

**Option B:** Membranous nephropathy is another cause of nephrotic syndrome, often presenting with heavy proteinuria and normal hematuria. However, it does not typically involve recurrent episodes of gross hematuria following upper respiratory tract infections.

**Option C:** Post-streptococcal glomerulonephritis (PSGN) is an immune complex-mediated glomerulonephritis that often occurs after a streptococcal infection. While PSGN can present with hematuria and proteinuria, it typically has a more acute presentation and does not usually involve recurrent episodes of gross hematuria following upper respiratory tract infections.

**Option D:** Lupus nephritis is a complication of systemic lupus erythematosus (SLE) and can present with hematuria and proteinuria. However, the presence of positive ANA and ANCA tests in this case makes SLE a less likely diagnosis.

**Clinical Pearl / High-Yield Fact**
IgA nephropathy is the most common cause of recurrent hematuria worldwide, and its diagnosis often requires a renal biopsy to confirm the presence of IgA deposits in the glomeruli.

**Correct Answer:** C. Post-streptococcal glomerulonephritis (PSGN) is an immune complex-mediated glomerulonephritis that often occurs after a streptococcal infection. While PSGN can present with hematuria and proteinuria, it typically has a more acute presentation and does not usually involve recurrent episodes of gross hematuria following upper respiratory tract infections.