Which of the following is a cause of high anion gap metabolic acidosis?

• A. Methanol
• B. Hyperlipidemia
• C. Hyperkalemia
• D. Hypophosphatemia

Answer: (A)

High anion gap metabolic acidosis happens when acids that add unmeasured anions accumulate in the blood. Methanol is metabolized to formic acid, which increases these unmeasured anions and raises the anion gap. Clinically this toxin often presents with an osmolar gap as well, but the acid-base disturbance specifically comes from formate accumulation after methanol metabolism.

The other options don’t produce this pattern. Hyperlipidemia affects lipid levels and can interfere with some lab measurements in a way that’s unrelated to the anion gap. Hyperkalemia and hypophosphatemia are electrolyte disorders; they don’t, by themselves, create a high anion gap metabolic acidosis.