Cystic fibrosis (CF) is a multi-organ disease, which mainly affects the respiratory and digestive systems. It is a genetic disorder due to an altered gene, i.e., the CFTR gene. The sweat test is the gold standard for the diagnosis of CF, also used in newborn screening (NBS) programs and to assess the response to treatment with new modulators. Nevertheless, it is well known that sweat test may give false negative or positive results, with a rate ranging from 10 to 15% [
206]. Patients with other underlying disorders, i.e., celiac disease, Klinefelter Syndrome, coprostasis in treatment with polyethylene glycol may show false positive sweat test. Cimbalo et al. have tried to explain the reason of this [
207], discriminating false positive and false negative sweat test results into 3 categories, i.e., ‘‘likely’’, ‘‘probable but needs validation,’’ and ‘‘unlikely’’ results based on the number of cases reported and use of genetic testing to exclude CF. They concluded that clinicians must aware the possibility of other conditions, such as adrenal insufficiency, even if two CFTR mutations are identified [
208]. They also recommend repeating the sweat test and/or genetic analyses twice, possibly in specialized laboratories [
209]. The mutated protein produced by CFTR gene does not work properly and leads to the production of thick mucus and sweat very rich in salts. The secretions of people with CF contain purulent material, polymerized DNA, and filamentous actin (F-actin) proteins derived from dead inflammatory cells and epithelial cells and very little mucin. This has important therapeutic implications. Terlizzi et al. [
210] have emphasized that at present symptomatic mucolytic treatment of patients with CF includes the inhalation of DNase, hypertonic saline or mannitol combined with chest physiotherapy. Several articles have shown that there is no superiority of hypertonic saline than other mucolytic agents, even if the benefits are that it’s an inexpensive, safe, and effective additional therapy [
211,
212]. It is possible the use of more than one inhaled solution at the same time, to achieve more benefit since these agents have different mechanisms of action [
213]. Accordingly, authors recommend the dornase alfa as the first choice in routine treatment and if the clinical response is inadequate, hypertonic saline is proposed alone or in combination with dornase alfa.