Unveiling the Deceptive Diagnosis: Exploring False-Positive Ethylene Glycol Poisoning

Introduction: Ethylene glycol (EG) poisoning can lead to significant mortality if left untreated. When unable to elicit exposure history, determining blood EG levels becomes critical for diagnosis and guides antidote administration. While gas chromatography is gold standard for diagnosis, its utility is limited due to restricted availability. Surrogate diagnostic tests are often used and should be interpreted with caution. Case Description: A 66-year-old female with history of alcohol use disorder and COPD presented with dyspnea and confusion. History of EG ingestion could not be obtained. She was hypotensive, tachycardic, in respiratory distress and had decreased breath sounds bilaterally. Laboratory work showed pancytopenia, respiratory and metabolic acidosis (pH 6.87), anion gap of 31 mmol/L, osmolol gap of 9 mOsm/kg, and lactic acidosis (17.4 mmol/L). A right lower lobe lung opacity on CT raised suspicion for respiratory source of septic shock. She was emergently intubated, treated with IV fluids, antibiotics, vasopressors, and initially got fomepizole for severe EG toxicity after spectrophotometric assay revealed elevated EG levels of 49 mg/dL. Since no calcium oxalate crystals were present on urine sediment (Image) and the osmolal gap was normal, the blood sample taken upon admission, which indicated elevated EG levels, was subjected to gas chromatography coupled with mass spectrometry. It resulted negative for EG. Due to worsening acidosis and anuria, CRRT was initiated with no improvement and she passed away. Respiratory culture resulted positive for staphylococcus, making pneumonia and sepsis a likely diagnosis. Discussion: EG levels can be falsely elevated by spectrophotometry in presence of severe lactic acidosis. It uses enzymatic method to detect nicotinamide adenine dinucleotide levels produced by oxidation of both EG and lactic acid. This leads to misdiagnosis and use of inappropriate and costly therapies. Thus, laboratory tests should be interpreted with caution. When suspicion for EG toxicity is high in patients with lactic acidosis, gas chromatography coupled with mass spectrometry should be used.Urine without calcium oxalate crystals.