A Rare Case of Elevated Osmolar Gap in Diabetic Ketoacidosis/Hyperosmolar Hyperglycaemic State in the Absence of Concomitant Toxic Alcohol Ingestion

The serum osmolar gap, defined as the difference between measured osmolality and calculated osmolarity, is a convenient method to screen for toxins in serum. In normal circumstances, the difference between the two is 6–10 mol/kg. Typical contributors to serum osmolarity are sodium bicarbonate, sodium chloride, glucose and urea. An elevated gap, defined as a difference >10 mol/kg, can occur if a sufficient quantity of an additional solute other than those mentioned above is present in the serum or there are inaccuracies in sodium measurement secondary to hyperlipidaemia and hyperproteinaemia. An elevated serum osmolar gap should thus prompt clinicians to check for toxic alcohol levels. Treatment with fomepizole should not be delayed if suspicion is high. Isolated diabetic ketoacidosis can occasionally present with an elevated osmolar gap in the absence of concomitant alcohol ingestion. This finding is attributed to the production of acetone and glycerol. We describe the case of a 62-year-old man presenting with diabetic ketoacidosis/hyperosmolar hyperglycaemic state and an elevated osmolar gap in the absence of toxic alcohol ingestion. LEARNING POINTS: The osmolar gap is the difference between the measured and the calculated serum osmolarity and should be calculated in all patients presenting with elevated serum osmolarity; if elevated, toxic alcohol ingestion should be considered and prophylactic treatment with fomepizole immediately administered if the index of suspicion is high. Although toxic alcohol ingestion is one of the common causes of an elevated osmolar gap, hyperlipidaemia, hyperproteinaemia and less occasionally lactic acidosis and ketoacidosis have also been implicated. In the setting of ketoacidosis, the osmolar gap can be elevated in the absence of toxic alcohol ingestion, is attributed to increased production of acetone and glycerol, and is responsive to treatment with insulin and intravenous fluids.