17th February 2025

Cystic fibrosis (CF)

Overview of CF

Cystic fibrosis is a genetic condition characterised by an abnormality in salt and water transport, resulting in thick, sticky mucus that can block the lungs and digestive system.

Genetics of CF

Cystic fibrosis has an autosomal recessive inheritance caused by a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) (chromosome 7), which is a chloride channel in cells that line the lungs, pancreas, digestive tract, sweat glands and reproductive organs.

There are over 200 genetic mutations associated with CF, but the commonest is deletion of the 508th amino acid (∆508).

Diagnosis of CF

Cystic fibrosis is mostly now picked up at birth via heel-prick testing in the UK (blood spot immunoreactive trypsin test), although, rarely, milder disease may present later. This can be confirmed by a sweat test (people with cystic fibrosis tend to have high levels of chloride in their sweat) and genetic screening.

Clinical features of CF

Viscous secretions in the lungs can cause recurrent chest infections and subsequent bronchiectasis.

In the pancreas, secretions can block exocrine ducts, leading to pancreatic enzyme insufficiency (malabsorption, steatorrhoea) and pancreatic destruction, causing diabetes mellitus.

Thickened secretions in the reproductive organs can cause infertility, reduced fertility and delayed puberty. Fertility issues are often more severe in men than women, due to congenital bilateral absence of the vas deferens.

Patients with cystic fibrosis are also at high risk of intestinal obstruction; meconium ileus is seen in newborns.

Management of CF

The mainstay of management is respiratory physiotherapy, such as postural drainage techniques to help clear viscous sputum and avoid chest infections. Other aspect of management may include:

• Pancreatic enzyme supplementation – to treat pancreatic insufficiency
• Specialised diet – high in calories, fat and salt to counteract malabsorption
• Mucolytics – to help break down thickened sputum
• Antibiotics for recurrent infections – patients with CF generally need longer courses and higher doses. Pseudomonas aeruginosa cover should always be considered, especially if the patient has been previously infected. This is a common coloniser in patients with cystic fibrosis and is identified by Gram-negative rods on blood cultures.
• Lung transplantation – bilateral lung transplant is usually the procedure of choice and should be considered once a patient is on optimal medical therapy and their disease is impacting their quality of life
• Routine immunisations and yearly flu vaccine

References

• Chapman S. Oxford handbook of respiratory medicine. Oxford; New York: Oxford University Press; 2005
• National Institute for Health and Care Excellence. Cystic fibrosis: diagnosis and management [Internet]. 2017 [cited 2022 Jan 31] Available from: https://www.nice.org.uk/guidance/ng78/resources/cystic-fibrosis-diagnosis-and-management-pdf-1837640946373
• August 2 Pool JJ, 2019 [cited 2022 Jan 31] Diet and Nutrition Considerations with Cystic Fibrosis [Internet]. Cystic-Fibrosis.com. Available from: https://cystic-fibrosis.com/diet-nutrition