The diagnosis of CF is based on phenotypic features, a history of CF in a sibling, or a positive newborn screening result. The diagnosis is confirmed by measuring increased chloride concentration in sweat or the identifying 2 CF causing mutations of CFTR. The majority of patients are diagnosed by 2 years of age. Because not all the CFTR mutations can be identified with routine molecular methods, universal mutational screening for CF is not recommended. However all pregnant women are offered the opportunity for carrier detection.