A 19-year-old girl develops sudden-onset non-bloody diarrhea. She was previously well and is not taking any medications or traveled anywhere recently. Her abdomen is soft and non-tender on examination, and the anion gap is normal.For the above patient with new symptoms, select the most likely acid base disorder.: (A) metabolic acidosis, (B) metabolic alkalosis, (C) respiratory acidosis, (D) respiratory alkalosis
Answer is A. She has a non-anion gap metabolic acidosis because of bicarbonate loss from the diarrhea. The anion gap is calculated as the sodium concentration minus the chloride plus the bicarbonate concentration. Other causes of bicarbonate loss with normal anion gap include proximal RTA and primary hyperparathyroidism.