<prompt> An infant has a positive newborn screening test for cystic fibrosis. What cut off of sweat chloride confirms cystic fibrosis?Sweat chloride 30 mEqLSweat chloride 40 mEqLSweat chloride 50 mEqLSweat chloride 60 mEqL  <response>: 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 mEqL of chloride in sweat is diagnostic of CF when 1 or more other criteria are present. 