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: Pediatrics
A 3–month old male child with normal genitalia presents to the emergency department with severe dehydration, hyperkalemia and hyponatremia. The measurement blood levels of which of the following will be helpful? 
Select and explain. 
A. 17–hydroxy progesterone, B. Renin, C. Cortisol, D. Aldosterone
A: 17–hydroxy progesterone
Answer: A: 17–hydroxy progesterone 
Explanation: This is a case of congenital adrenal hyperplasia due to deficiency of 21 - hydroxylase deficiency.
Because of the enzyme block ,there is increased formation of 17- hydroxyprogesterone, which is then shunted into the production of testosterone.
Levels of cortisol and aldosterone are reduced.