Toxic Alcohol Ingestions and Osmolal Gap

Introduction to Osmolal Gap

The osmolal gap is the difference between measured serum osmolality and calculated osmolality, with normal values typically <10 mOsm/kg, as suggested by the American Diabetes Association 1, 2
The osmolal gap can be calculated using the formula: Estimated osmolality = 2 × [Na⁺] + [Glucose]/18 + [BUN]/2.8, and then subtracting the estimated osmolality from the measured osmolality to determine the osmolal gap, with normal values typically <10 mOsm/kg 1

Ethylene glycol ingestion causes severe metabolic acidosis and an osmolal gap >50 with fomepizole or >20 with ethanol therapy, which warrants extracorporeal treatment, as recommended by the EXTRIP workgroup guidelines and the American College of Medical Toxicology 1
The presence of calcium oxalate and hippurate crystals in urine suggests ethylene glycol ingestion, according to the American Association of Clinical Endocrinologists 2
If ethylene glycol poisoning is suspected, fomepizole should be started immediately, and hemodialysis should be considered if osmolal gap >50 with fomepizole or >20 with ethanol therapy, as suggested by the EXTRIP workgroup guidelines 1

Diabetic ketoacidosis (DKA) can present with both elevated osmolal gap and high anion gap metabolic acidosis, with diagnostic criteria including plasma glucose >250 mg/dL, arterial pH <7.3, bicarbonate <15 mEq/L, as recommended by the American Diabetes Association 2

Laboratory confirmation with specific toxic alcohol levels is essential for treatment decisions, including fomepizole administration and hemodialysis, as noted by the EXTRIP workgroup guidelines 1
An osmolal gap >20 with suspected ethylene glycol poisoning suggests the need for extracorporeal treatment (ECTR) if ethanol is being used as an antidote, according to the EXTRIP workgroup guidelines 1
An osmolal gap >10 with suspected ethylene glycol poisoning warrants ECTR if no antidote is available, as recommended by the EXTRIP workgroup guidelines 1
Freezing point depression osmometry is required to accurately detect volatile substances like ethanol, as vapor pressure osmometry may miss ethanol's contribution, potentially leading to diagnostic errors 3
Laboratory tests should include specific toxic alcohol levels, glycolate level, serum lactate, and urine for calcium oxalate crystals to confirm the diagnosis and monitor the patient's condition 1
Relying solely on osmolal gap can be misleading, as the gap may normalize as toxic alcohols are metabolized to their toxic metabolites, highlighting the importance of clinical suspicion and prompt treatment, as noted by the EXTRIP workgroup guidelines 1

Normal osmolal gap values are typically <10 mOsm/kg; values >20 mOsm/kg often suggest toxic alcohol ingestion, and ethanol alone can cause a marked increase in osmolal gap, sometimes exceeding 90 mOsm/kg in severe intoxication 1
The osmolal gap due to ethanol can be estimated using the formula: Osmolal Gap = 0.23 × (Ethanol [mg/dL]) - 1.43, and when calculating the osmolal gap, use the formula: 1.86 × (Na⁺ + K⁺) + 1.15 × glucose + urea + 14 (all in mmol/L) 3
An elevated osmolal gap with high ethanol levels may not require additional workup for other toxic alcohols if the gap can be fully explained by the ethanol concentration 1