Acute nephritic syndrome and glomerulonephritis — structured clinical encounter

A six-year-old boy is brought to the emergency department with two days of cola-coloured urine and periorbital puffiness that is worse in the mornings. Two weeks earlier he had a sore throat and fever, treated with paracetamol. He is afebrile, alert and not distressed, but has periorbital and mild pretibial oedema. His blood pressure is 125/82 mmHg, above the 95th percentile for his age, sex and height. His heart sounds are normal with no murmur, his chest is clear, and his abdomen is soft with no organomegaly. Urinalysis shows 3+ blood and 1+ protein; microscopy reveals dysmorphic red cells and red-cell casts. His creatinine is 78 micromoles per litre, serum albumin 34 g per litre, and his serum C3 is 0.42 g per litre with a normal C4. His ASO titre is markedly raised and his anti-DNase B is positive. A renal ultrasound shows normal-sized kidneys with no obstruction.