Calcium Oxalate Monohydrate Crystals: A Clue to Ethylene Glycol Poisoning

Abstract

A 52-year old man presented to the emergency department in an obtunded state; no history was obtainable. Initial arterial blood gas showed pH 7.12; pCO2 11 mm Hg; and HCO3 4 mEq/L. The plasma anion gap was 21 mEq/L, and the plasma osmolal gap was 6 mOsm/Kg H2O. Initial serum creatinine was 2.33 mg/dL and blood urea nitrogen was 19 mg/dL. Urinalysis with microscopy showed numerous crystals, which resembled hippuric acid crystals (Figure 1). Under polarized light, the crystals showed strong positive birefringence, characteristic of calcium oxalate monohydrate crystals (Figure 2). Given the clinical, laboratory, and urine microscopy findings of calcium oxalate monohydrate crystals, a diagnosis of ethylene glycol poisoning was made (which was later confirmed by the patient once he regained consciousness). The patient was successfully treated with 8 hours of hemodialysis and fomepizole on the day of admission. He subsequently required 1 more session of hemodialysis for rising serum creatinine and uremia. Renal function subsequently stabilized, and at the time of follow-up 2 weeks later, his serum creatinine had decreased from 6.4 mg/dL to 2.5 mg/dL. Although the crystals were originally interpreted as hippuric acid crystals, urine microscopy was instrumental in making the diagnosis. Calcium oxalate monohydrate crystals, which resemble hippuric crystals and are highly specific for ethylene glycol poisoning, 1. Godolphln W. Meagher E.P. Sanders D. et al. Unusual calcium oxalate crystals in ethylene glycol poisoning. Clin Toxicol. 1980; 16: 479-486 Crossref PubMed Scopus (32) Google Scholar , 2. Huhn K.M. Rosenberg F.M. Critical clue to ethylene glycol poisoning. Can Med Assoc J. 1995; 152: 193-195 Google Scholar were identified by polarization showing strongly positive birefringent crystals. 3. Eder A.F. McGrath C.M. Dowdy Y.G. et al. Ethylene glycol poisoning: toxicokinetic and analytical factors affecting laboratory diagnosis. Clin Chem. 1998; 44: 168-177 PubMed Google Scholar This prompt recognition allowed the patient to receive life-saving treatment in a timely manner. The presence of calcium oxalate monohydrate crystals is very rare in either normal urine or in association with calcium oxalate calculi. Figure 2 View Large Image Figure Viewer