Oxalate Crystals in Ethylene Glycol Poisoning
Calcium oxalate crystals in urine are pathognomonic for ethylene glycol poisoning and indicate that toxic metabolism has already occurred, requiring immediate antidote therapy with fomepizole and consideration for hemodialysis based on severity markers. 1, 2
Significance of Oxalate Crystals
Diagnostic Value
- Calcium oxalate monohydrate crystals (needle-shaped or "hemp seed" habit) are the predominant crystal type found in ethylene glycol poisoning, though envelope-shaped dihydrate crystals may occasionally appear 3, 4
- These crystals typically appear 3-6 hours after ingestion, coinciding with the onset of metabolic acidosis 2
- Crystal detection may be the only real-time confirmation of diagnosis when ethylene glycol has already been metabolized and blood levels are undetectable 4, 5
- However, crystals alone are NOT an indication for hemodialysis—they help diagnose poisoning but treatment decisions must be based on other severity markers 6
Pathophysiologic Mechanism
- Crystals form when oxalic acid (the final toxic metabolite of ethylene glycol) precipitates with calcium in the renal tubules 2
- This crystal deposition causes acute tubular necrosis and acute kidney injury, which can progress to chronic kidney disease in 16.8% of survivors 1, 2
- The presence of crystals indicates that toxic metabolism is already underway, making immediate intervention critical 1
Treatment Algorithm
Immediate Antidote Therapy (Upon Suspicion)
- Administer fomepizole 15 mg/kg loading dose immediately upon suspicion based on history, anion gap metabolic acidosis, increased osmolar gap, visual disturbances, OR oxalate crystals in urine 1, 7
- Follow with 10 mg/kg every 12 hours for 4 doses, then 15 mg/kg every 12 hours until ethylene glycol <20 mg/dL and patient is asymptomatic with normal pH 7
- Ethanol (100-150 mg/dL) is an alternative if fomepizole is unavailable, but requires careful monitoring 1
Hemodialysis Indications (Any One Criterion)
Hemodialysis is strongly recommended when ANY of the following are present: 6, 1
- Anion gap >27 mmol/L (with potassium in calculation)
- Glycolate concentration >12 mmol/L
- Ethylene glycol concentration ≥50 mg/dL (≥50 mmol/L with fomepizole)
- Stage 2 or 3 acute kidney injury (KDIGO criteria)
- Coma or seizures
- Significant or worsening metabolic acidosis despite supportive care
Hemodialysis Technical Considerations
- Intermittent hemodialysis is the preferred modality for faster removal of ethylene glycol and metabolites 1
- Increase fomepizole dosing to every 4 hours during hemodialysis (fomepizole is dialyzable) 1, 7
- Continuous kidney replacement therapy (CKRT) is second-line if intermittent hemodialysis unavailable or marked brain edema present 1
- Stop hemodialysis when: anion gap <18 mmol/L, ethylene glycol <25 mg/dL (4 mmol/L), or acid-base abnormalities corrected 1
Supportive Care
- Sodium bicarbonate for severe metabolic acidosis 1
- Thiamine and pyridoxine as cofactors to enhance metabolism of toxic intermediates 1
- Mechanical ventilation if respiratory failure develops 1
- Vasopressors for refractory hypotension 1
Critical Pitfalls to Avoid
- Never rely solely on reported ingestion dose for treatment decisions—always confirm with laboratory markers 6, 1
- Do not wait for ethylene glycol blood levels to initiate fomepizole—treat based on clinical suspicion and crystals 7, 4
- Ethylene glycol concentrations diminish as metabolites accumulate, so both parent compound AND acid-base status must guide treatment 1, 7
- Anion gap may overestimate or underestimate glycolate levels—use multiple parameters together 1
- Monitor for alcohol withdrawal in patients with alcohol use disorder, especially during hemodialysis 1