After the exclusion of CF, the diagnostic algorithm verifies a CFTR dysfunction in 2 different functional tests (sweat test, nasal potential difference measurement (NPD) or the intestinal current measure (ICM)), OR 1 CFTR variant and dysfunction in at least 2 different functional tests OR 2 CFTR variants with maximum 1 CF causing [38]. Here, CFTR is linked to cystic fibrosis.