A metabolic acidosis with an elevated anion gap typically indicates what?

• A. Accumulation of unmeasured anions (e.g., lactate, ketoacids)
• B. Loss of bicarbonate with normal chloride
• C. Respiratory acidosis
• D. Hyperchloremia without acid gain

Answer: (A)

An elevated anion gap in metabolic acidosis means there are extra, unmeasured anions accumulating in the blood. The anion gap is the difference between measured cations and anions, primarily calculated as sodium minus (chloride plus bicarbonate). When this gap widens, it indicates acids that aren’t normally measured—such as lactate, ketoacids, sulfates, phosphates, or toxins—are piling up. This is typical of conditions like lactic acidosis from poor tissue oxygenation, diabetic or alcoholic ketoacidosis, renal failure with retention of organic acids, or ingestion of certain toxins (for example methanol or ethylene glycol).

In contrast, normal anion gap metabolic acidosis occurs when bicarbonate is lost and chloride rises to maintain electroneutrality, such as with diarrhea or certain renal tubular acidoses. Respiratory acidosis isn’t a metabolic acidosis at all, but a buildup of CO2 due to impaired ventilation, so it doesn’t involve the anion gap. Hyperchloremia without acid gain also leads to a normal, not elevated, anion gap.