Acute nephritic syndrome and glomerulonephritis — formative SAQs

SAQ 1 — Six-year-old with cola-coloured urine after a sore throat (10 marks, 15 minutes)

A six-year-old boy is brought to the emergency department with two days of smoky, cola-coloured urine and puffiness around his eyes that is worse in the morning. His mother reports he had a sore throat and fever two weeks ago, treated with paracetamol only. On examination he is afebrile, has periorbital and pretibial oedema, a blood pressure of 125/82 mmHg (above the 95th percentile for his age, sex and height), and a quiet chest. His urinalysis shows 3+ blood and 1+ protein, with dysmorphic red cells and red-cell casts on microscopy. His creatinine is mildly elevated at 78 micromoles per litre. His serum C3 is low at 0.42 g per litre and his C4 is normal. His ASO titre is markedly raised. [1] [3]

a) Define the acute nephritic syndrome and state the four clinical features that, taken together, establish the diagnosis in this child. Explain why the two-week interval between the sore throat and the onset of nephritis is the expected latent period for a pharyngeal streptococcal trigger. (4 marks) [1] [3]

b) Interpret his complement results. Why does a low C3 with a normal C4 support post-streptococcal glomerulonephritis, and what single follow-up blood test will you arrange at six to eight weeks to confirm the diagnosis? State the finding that would contradict uncomplicated post-streptococcal GN and mandate renal biopsy. (4 marks) [2] [11]

c) Outline your immediate management, naming the diuretic and its dose for his oedema, the antihypertensive class you would start, and the streptococcal eradication regimen. State one indication for paediatric intensive care or dialysis. (2 marks) [1] [3]