This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cystic fibrosis & Sleep apnea, Subject name: Medicine
An infant has a positive newborn screening test for cystic fibrosis. What cut off of sweat chloride confirms cystic fibrosis? 
Select and explain. 
A. Sweat chloride > 30 mEq/L, B. Sweat chloride > 40 mEq/L, C. Sweat chloride > 50 mEq/L, D. Sweat chloride >60 mEq/L
D: Sweat chloride >60 mEq/L
Answer: D: Sweat chloride >60 mEq/L 
Explanation: The diagnosis of CF rests on the combination of clinical criteria and abnormal CFTR function as documented by sweat tests, nasal PD measurements, and CFTR mutation analysis. More than 60 mEq/L of chloride in sweat is diagnostic of CF when 1 or more other criteria are present.