Which condition is associated with an elevated anion gap?

• A. Renal Tubular Acidosis
• B. Diabetes Mellitus
• C. Metabolic Acidosis Due To Diarrhea
• D. Lactic Acidosis

Answer: (D)

An elevated anion gap occurs when there are extra unmeasured anions in the blood. The classic way we assess it is Na minus (Cl plus HCO3); when substances that aren’t routinely measured—like lactate, ketoacids, sulfate, phosphate—accumulate, the gap widens. Lactic acidosis fits this pattern because lactate adds to the unmeasured anions pool, driving the anion gap upward.

In contrast, metabolic acidosis from diarrhea is due to loss of bicarbonate with a compensatory increase in chloride, which keeps the anion gap normal. Renal tubular acidosis also produces a normal anion gap metabolic acidosis for the same reason—bicarbonate loss with chloride compensation. While diabetes mellitus can involve elevated anion gap in diabetic ketoacidosis, the most straightforward and consistently associated condition among the options is lactic acidosis, where lactate accumulation directly increases the unmeasured anions and raises the gap.