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: Biochemistry
Sweat chlorides are increased in: 
Select and explain. 
A. Addison's disease, B. Conn's syndrome, C. Cystic fibrosis, D. Phaeochromocytoma
C: Cystic fibrosis
Answer: C: Cystic fibrosis 
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. Elevated sweat Cl- values are nearly pathognomonic for CF. The sweat concentration values for Cl- (and Na+) vary with age, but, typically, a Cl- concentration of >70 meq/L in adults discriminates between CF and other lung diseases. Ref: Boucher R.C. (2012). Chapter 259. Cystic Fibrosis. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.