Match each clinical presentation of acute renal dysfunction with the most characteristic finding expected on microscopic urinalysis.
- Oliguric acute kidney injury following prolonged intraoperative hypotension during an abdominal aortic aneurysm repair.Muddy brown granular casts
- Severe high anion gap metabolic acidosis and acute kidney injury following ingestion of a sweet-tasting, unknown liquid.Calcium oxalate crystals (envelope-shaped)
- Rapidly worsening renal function, palpable purpura, and low serum complement levels in a patient with chronic hepatitis C.Red blood cell casts and dysmorphic erythrocytes
- Rising serum creatinine, low-grade fever, and a diffuse maculopapular rash developing two weeks after initiating intravenous nafcillin.White blood cell casts and eosinophils
Answer
Ischemic hypotension causes muddy brown granular casts; ethylene glycol toxicity produces calcium oxalate crystals; cryoglobulinemic glomerulonephritis leads to red blood cell casts; and nafcillin-induced interstitial nephritis generates white blood cell casts.
Urinary sediment serves as a 'liquid biopsy' that non-invasively distinguishes the anatomical compartment of renal injury. Ischemic damage exclusively targets tubular cells (ATN), yielding granular casts. Toxic ingestions like ethylene glycol have specific metabolites (oxalate) that crystallize. Glomerular inflammation (glomerulonephritis) uniquely allows red blood cells to cross the damaged basement membrane, forming RBC casts. Finally, allergic tubulointerstitial reactions (AIN) recruit inflammatory cells, forming WBC casts.
Step-by-Step Solution
Key Concept
Correlation of acute kidney injury etiologies with specific urinary sediment findings.