This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of pituitary gland, Subject name: Medicine
The syndrome of inappropriate ADH secretion is characterized by the following: 
Select and explain. 
A. Hyponatremia and urine sodium excretion > 20 mEq/L, B. Hypernatremia and urine sodium excretion > 20 mEq/L, C. Hyponatremia and hyperkalemia, D. Hypernatremia and hyperkalemia
A: Hyponatremia and urine sodium excretion > 20 mEq/L
Answer: A: Hyponatremia and urine sodium excretion > 20 mEq/L 
Explanation: In SIADH, the excessive retention of water expands extracellular and intracellular volume. This explains Dilutional Hyponatremia. Since the urine is concentrated hence urine sodium mEq/unit of time can be explained. Another plausible explanation is that expanded volume leads to release of ANF and resultant natriuresis explains the urine sodium> 20mEq/L. Hyponatremia sub-classified according to volume status Clinical example Sodium levels TBW Hypovolemic Hyponatremia Diarrhea Cerebral salt wasting Low Low Euvolemic Hyponatremia SIADH Normal Increased Hypervolemic Hyponatremia CHF Cirrhosis Nephrotic Increase Increased