Cystic fibrosis (CF), termed after the autopsy findings of “cystic fibrosis of the pancreas” in malnourished infants, is caused by mutations in the gene that encodes for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The CFTR protein functions on the apical surface of epithelial cellsas a cyclic AMP-dependent chloride channel, a bicarbonate channel and as a modulator of other ion channels.

CF can be classified according to the exocrine pancreatic function status - pancreatic insufficient (PI) or sufficient (PS). The PS status has its unique phenotypic and genotypic characteristics. Clinicians often only consider the possibility of CF when a patient presents with the “classic” manifestations of CF – multi-organ disease and symptoms related to PI. However, patients who presents with CF disease in late childhood and adulthood often present differently with single-organ manifestations only and are usually PS. Patients with PS status are at risk of developing pancreatitis and progressing to PI.

The diagnosis of CF is straightforward in the presence of a CF phenotype PLUS abnormal sweat chloride and/or 2 CF-causing mutations. This is usually the case among patients who present with the “classic” manifestation of CF. However, among symptomatic patients who present with disease in adulthood, the diagnostic outcomes may be indeterminate. The term “CFTR-related disorder” is used to define symptomatic individuals who are affected by CFTR dysfunction but do not fulfil the criteria for CF. The role of sweat test, genotyping and other methods of ion channel function measurements will be discussed.