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Diagnostic Tests: Oxalate Crystals in Ethylene Glycol Poisoning
Overview — What These Are
The crystals shown are envelope-shaped calcium oxalate crystals, which appear in the urine after ingestion of ethylene glycol, a toxic alcohol found in antifreeze. When ethylene glycol is metabolized, one of its byproducts is oxalic acid, which binds calcium to form calcium oxalate crystals. These crystals can precipitate in the renal tubules, leading to obstruction, inflammation, and ultimately acute tubular necrosis (ATN). Their presence in a patient with metabolic acidosis strongly suggests ethylene glycol poisoning.
Most Accurate Diagnostic Test
The most accurate and definitive test for diagnosing ethylene glycol intoxication is the serum ethylene glycol level.
Other supportive findings include:
- Urinary fluorescence under a Wood’s lamp (can be transient and unreliable)
- Hypocalcemia, because oxalic acid binds serum calcium
- Calcium oxalate crystals on urinalysis
However, a measured blood ethylene glycol level is the gold standard for diagnosis.
When This Is the Correct Answer
Think of ethylene glycol overdose when a case presents with:
- High anion gap metabolic acidosis
- Altered mental status, often in the context of a suicide attempt or accidental ingestion
- Hypocalcemia, which may produce QT prolongation or arrhythmias
- Acute renal failure due to tubular deposition of oxalate crystals
- Calcium oxalate crystals in the urine (classic finding)
Patients often present after ingesting antifreeze, which is sweet-tasting, making it a common agent in intentional or accidental toxic ingestion. The metabolic acidosis is often severe, and kidney injury progresses rapidly without treatment.
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