This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluids and Electrolyte Imbalance, Subject name: Medicine
Most common cause of hypernatremia? 
Select and explain. 
A. Primary hypodipsia, B. Carcinoid syndrome, C. Renal losses, D. Sweating
A: Primary hypodipsia
Answer: A: Primary hypodipsia 
Explanation: Elderly individuals with reduced thirst and/or diminished access to fluids are at the highest risk of developing hypernatremia. Patients with hypernatremia may rarely have a central defect in hypothalamic osmoreceptor function, with a mixture of both decreased thirst and reduced AVP secretion