Question of the Week

For January 22, 2019

A 20-year-old male college student presents for evaluation of a rash that developed gradually during the past 3 days. Two weeks ago, he began a 10-day course of amoxicillin for streptococcal pharyngitis. He takes no other medications. His medical history is unremarkable. A paternal uncle has Alport syndrome.

His blood pressure is 140/85 mm Hg, his heart rate is 100 beats per minute, and his temperature is 37.5°C. Physical examination reveals a diffuse, erythematous maculopapular rash, predominantly across the trunk.

Laboratory testing yields the following results:

Patient value

Reference range

Hemoglobin (g/dL)

13.5

13.5–17.5

Leukocyte count (per mm3)

9600

4500–11,000

Creatinine (mg/dL)

2.4

0.8–1.3

Urea nitrogen (mg/dL)

32

10–20

Complement C3 (mg/dL)

92

86–184

Complement C4 (mg/dL)

36

20–58

The platelet count and leukocyte differential are normal. Urinalysis shows 1+ protein, 1–3 red cells per high-power field (reference range, 0–2), and 10–20 white cells per high-power field (0–2). A Gram stain of the urine specimen is negative.

Renal ultrasonography shows normal-size kidneys without hydronephrosis.

Which one of the following conditions is the most likely explanation for acute kidney injury in this patient?

Poststreptococcal glomerulonephritis
Alport syndrome
Immunoglobulin A nephropathy
Acute tubular necrosis
Acute interstitial nephritis