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Difficulty: MediumNephrology

Match each clinical presentation and urinalysis finding with the most likely underlying renal pathology.

  • A 62-year-old man develops oliguria and a rising serum creatinine two days after receiving intravenous contrast for a CT angiogram. Urinalysis reveals muddy brown granular casts.Acute tubular necrosis
  • A 28-year-old man presents with fever, a maculopapular rash, and acute kidney injury five days after starting nafcillin. Urinalysis reveals white blood cell casts and eosinophiluria.Acute interstitial nephritis
  • A 34-year-old woman presents with hypertension, periorbital edema, and cola-colored urine one week after recovering from impetigo. Urinalysis reveals red blood cell casts.Glomerulonephritis
  • A 50-year-old man with poorly controlled diabetes mellitus presents with generalized edema and a serum albumin of 2.1 g/dL2.1 \text{ g/dL}. Urinalysis reveals fatty casts and oval fat bodies.Nephrotic syndrome

Answer

Contrast-induced injury with muddy brown casts matches Acute tubular necrosis. Nafcillin-induced injury with WBC casts matches Acute interstitial nephritis. Post-impetigo injury with RBC casts matches Glomerulonephritis. Diabetic nephropathy with fatty casts matches Nephrotic syndrome.
The correct pairings rely on identifying the hallmark urinalysis findings and clinical risk factors for each renal pathology. Acute tubular necrosis is characterized by muddy brown casts following an ischemic or nephrotoxic insult. Acute interstitial nephritis is indicated by white blood cell casts and eosinophils following exposure to an offending drug. Glomerulonephritis is diagnosed by red blood cell casts in the setting of nephritic syndrome symptoms. Nephrotic syndrome presents with heavy proteinuria, hypoalbuminemia, and fatty casts.

Step-by-Step Solution

1
Analyze the first patient's history of recent radiocontrast administration and the presence of muddy brown granular casts.
Identify this pattern as characteristic of acute tubular necrosis (ATN).
Contrast is a known nephrotoxin that damages tubular cells, which slough off and form muddy brown casts.
2
Evaluate the second patient's presentation of fever, rash, and new medication exposure (nafcillin) alongside white blood cell casts.
Identify this pattern as acute interstitial nephritis (AIN).
AIN is an allergic inflammatory reaction in the kidney interstitium, often drug-induced, characterized by WBCs and eosinophils.
3
Assess the third patient's post-infectious presentation (impetigo) featuring hypertension, edema, and red blood cell casts.
Identify this pattern as glomerulonephritis.
RBC casts form when red blood cells leak through a damaged glomerular basement membrane, a hallmark of acute nephritic syndrome.
4
Review the fourth patient's long-standing diabetes, profound hypoalbuminemia, and fatty casts in the urine.
Identify this pattern as nephrotic syndrome.
Severe proteinuria leads to hypoalbuminemia and a compensatory increase in hepatic lipid synthesis, resulting in lipiduria (fatty casts).

Key Concept

Urinalysis sediment interpretation in the differential diagnosis of acute kidney injury and proteinuric states.
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Topics

Nephrology

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