Diagnosis typically relies on “classic” clinical manifestations associated with abnormal sweat chloride measurements (≥60 mmol/L verified twice) or the presence of 2 CF-causing variants in trans. The diagnosis of CF or CFTR-RD may be challenging, especially in adults, in whom standard diagnostic criteria are not clearly fulfilled, and when other diagnoses, such as asthma and ABPA, may overlap with CF/CFTR-RD. This evidence concerns the gene CFTR and asthma.