This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid & Electrolyte, Subject name: Medicine
Acute hyponatremia becomes symptomatic at what level of serum sodium concentration? 
Select and explain. 
A. <130mEq/L, B. <125 mEq/L, C. <120 mEq/L, D. <115 mEq/L
C: <120 mEq/L
Answer: C: <120 mEq/L 
Explanation: Ans. is 'c' i.e., <120 mEq/L Acute Hyponatremia* Cases of acute hyponatremia are defined as those developed in < 48 hours of duration.* These patients are usually symptomatic if hyponatremia is severe i.e. < 120mEq/L.* These patients are at greatest risk of development of neurologic symptoms but rarely develop demyelination.* Sodium levels in these patients should be corrected to relatively higher levels quickly.