Which of the following is not a differential for high anion gap metabolic acidosis?

High anion gap metabolic acidosis is often associated with various conditions that lead to an accumulation of acids in the body, resulting in an increased anion gap. Conditions commonly associated with high anion gap include diabetic ketoacidosis, salicylate (acetylsalicylic acid) ingestion, and metaldehyde poisoning, as these scenarios involve the presence of organic acids or other acidic compounds.

Chronic obstructive pulmonary disease (COPD), on the other hand, primarily leads to respiratory acidosis due to impaired gas exchange and subsequent retention of carbon dioxide. While it can contribute to a metabolic acidosis in certain situations, such as in cases of respiratory failure or rarely in cases of lactic acidosis, it does not directly cause a high anion gap metabolic acidosis. Therefore, it is not considered a differential for high anion gap metabolic acidosis, as the conditions associated with it typically do not involve an accumulation of unmeasured anions, which is the hallmark of high anion gap acidosis.

Recognizing the difference in the underlying mechanisms of the various conditions is key to understanding why COPD does not fit within the context of high anion gap metabolic acidosis.