Which of the following is a cause of a high osmolal gap?

• A. Ethylene glycol intoxication
• B. DKA (diabetic ketoacidosis)
• C. Uremia
• D. Lactic Acidosis

Answer: (A)

A high osmolal gap happens when there is an extra, unmeasured osmotically active substance in the blood. The calculated osmolality uses sodium, glucose, and BUN, so anything that adds to osmolality but isn’t included in that calculation will widen the gap. Ethylene glycol is a classic example: after ingestion it raises the measured osmolality, but it isn’t accounted for in the calculation, producing a large osmolar gap. The other conditions listed mainly cause metabolic disturbances (like acidosis or elevated glucose) and don’t reliably produce a markedly elevated osmolal gap.