In nearly 25% of children under 3 months, the sweat test produces a quantity of sweat that does not meet international recommendations and is insufficient to allow reliable and reproducible biological analyzes in the sweat collected. In children between 3 and 12 months, this rate is about 10% when it should not exceed 5%. Insufficient amount of sweat prevents confirmation or reversal of the early diagnosis of cystic fibrosis and early treatment before irreversible complications of the disease.

In this trial, a new support of sweat collection (Macroduct® Advanced Model 3710 Sweat Collection System, Wescor) will be tested with the goal to increase the amount of sweat collected during the sweat test, in comparison with the clinical routine method.

Inclusion Criteria:

• Subject aged of 2 days to 12 months
• Indication of a sweat test prescribed by a clinician in a context of neonatal screening
• Clinically stable
• Well hydrated
• Not under treatment with mineralocorticoids

Exclusion Criteria:

• Subjects weighing less than 2 kg
• Subjects less than 48 hours old
• Presence of an acute infectious condition
• Presence of mineralocorticoid treatment