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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Normal anion gap is mostly due to  :
assistant
The correct answer is  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