Okay, let's tackle this question about post-streptococcal glomerulonephritis in children. The user provided the question and the correct answer as "D. Acute onset hematuria with elevated ASO titre." Wait, but the options are missing. Hmm, maybe the user forgot to include the options. Let me think.

First, I need to recall the key diagnostic criteria for PSGN. Classic symptoms include acute onset of hematuria, hypertension, edema, and elevated ASO titers. The core concept here is the immune response following a streptococcal infection, leading to glomerular inflammation. The ASO (antistreptolysin O) titre is a common test for recent strep infection. Now, the options might include other tests like BUN/Cr, urine dipstick, or imaging. Let me structure the explanation accordingly.

The correct answer is D because it combines the clinical presentation (hematuria) with a serological marker (ASO). Other options might be incorrect if they don't include both. For example, option A might be BUN/Cr, which is a general renal function test but not specific. Option B could be a urinalysis without ASO. Option C might be a renal ultrasound, which isn't diagnostic for PSGN. The clinical pearl here is to remember the triad of symptoms and the ASO titre. Let me make sure the sections are covered properly and the explanation is concise. Also, check for any missing options but proceed with the given correct answer.

**Core Concept**
Post-streptococcal glomerulonephritis (PSGN) is a pauci-immune, immune-complex-mediated glomerulonephritis occurring after a streptococcal infection. Diagnosis hinges on a **typical clinical triad** (hematuria, hypertension, edema) plus evidence of recent streptococcal infection (elevated antistreptolysin O [ASO] titre or streptococcal DNAase B).

**Why the Correct Answer is Right**
The correct answer combines **acute hematuria** (microscopic or gross) with **elevated ASO titre**, reflecting immune complex deposition in glomeruli after a preceding streptococcal infection (e.g., pharyngitis or impetigo). ASO titre quantifies antibodies against streptococcal toxins, confirming recent infection. This pairing is diagnostic when supported by clinical features like hypertension, edema, and oliguria.

**Why Each Wrong Option is Incorrect**
**Option A:** "Elevated BUN and creatinine" indicates renal impairment but is nonspecific and occurs in many glomerular diseases.
**Option B:** "Urine dipstick showing proteinuria" is common in glomerulonephritis but lacks specificity for PSGN.
**Option C:** "Renal ultrasound" detects structural abnormalities (e.g., hydronephrosis) but is normal in PSGN, which is a histopathological diagnosis.

**Clinical Pearl / High-Yield Fact**
PSGN typically follows a **group A *Streptococcus* infection** (e.g., pharyngitis or skin infection) after a 1–2 week incubation period. **ASO titre** is key to diagnosis, but

✓ Correct Answer: C. Mild proteinuria, hematuria, low ASO tire