Osmolal Gap without Anion Gap in a 43-Year-Old Man

A 43-year-old man presented to the emergency department (ED)3 2 h after ingesting 10 oz of antifreeze mixed with Gatorade in a suicide attempt. The antifreeze was green, of an unknown brand, and purchased at a local gas station. He subsequently confessed to his wife, who brought him to a community hospital ED. He denied abdominal pain, nausea, vomiting, urinary symptoms, or visual changes. Initial laboratory tests (Table 1) were clinically relevant for the following: arterial whole-blood pH, 7.34; P co2, 33 mmHg (4.4 kPa); serum bicarbonate, 18 mmol/L; serum ethanol, 10 mg/dL (2.17 mmol/L); and serum anion gap, 18 mmol/L. The serum osmolal gap (75 mOsm/kg) was calculated as follows: Osmolal gap = freezing-point depression osmometer value − (2 × [Na+] + [glucose]/18 + [blood urea nitrogen]/2.8 + [ethanol]/4.6), where the Na+ concentration is in millimoles per liter and the glucose, blood urea nitrogen, and ethanol concentrations are in milligrams per deciliter.View this table:Table 1. The patient's laboratory results on presentation, after transfer to the tertiary care center, and on hospital day 2 after hemodialysis.aWith the advice of the local Poison Control Center, the patient was given 15 mg/kg fomepizole intravenously. He was placed on suicide precautions and transferred to a tertiary care center for further evaluation and treatment. On arrival at the tertiary care ED 8 h after ingestion and 3 h after fomepizole administration, the patient had a normal mental status and normal vital signs. Thiamine (100 mg), folic acid (50 mg), and pyridoxine (50 mg) were administered intravenously as cofactors for secondary metabolic pathways. At that time, laboratory test results (Table 1) were clinically relevant for the following: arterial whole-blood pH, 7.39; P co2, 28 mmHg (3.7 kPa); serum bicarbonate, 18 mmol/L; creatinine, 1.1 mg/dL (97.2 μmol/L); lactate, 5.3 mmol/L; anion gap, 14 mmol/L; and osmolal gap, 72 mOsm/kg. No crystals were visible in the urine. QUESTIONS TO CONSIDER1. What are the major …