This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nephrology, Subject name: Medicine
The difference between sodium and chloride is low , the metabolic disorder in the patient would be? 
Select and explain. 
A. Metabolic acidosis, B. Metabolic alkalosis, C. Respiratory acidosis, D. Respiratory alkalosis
A: Metabolic acidosis
Answer: A: Metabolic acidosis 
Explanation: The question mentions that difference between sodium and chloride is low which is mathematically possible if serum chloride increases. Now physiologically speaking Chloride excretion occurs in urine along with ammonium in 1:1 ratio to maintain electroneutrality . If chloride in blood is more it means it was not lost in urine If chloride is not lost, H+ is not lost in form of ammonium Hence there is an increase of H+ in the body leading to Hyperchloremic Metabolic Acidosis This kind of presentation is seen with renal tubular acidosis type 1,2,4: ureterosigmoidostomy: alkali loss in urine.