This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Normal anion gap is mostly due to  : 
Select and explain. 
A. Unmeasured Na+ ion, B. Unmeasured Cl- ion, C. Unmeasured proteins, D. None of the above
C: Unmeasured proteins
Answer: C: Unmeasured proteins 
Explanation: Normal anion gap is due to Unmeasured proteins. Normally in the plasma, the concentration of anion and cations are equal to maintain electrical neutrality. Thus, no real anion gap exists in the plasma and this is purely a diagnostic concept. 
Guyton and Hall Textbook of medical physiology Pg-426