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Cystic fibrosis (CF)
CF is an autosomal recessive disease of the CFTR chloride channel that causes thick secretions in the lungs, pancreas, bowel and male genital tract; the diagnosis is confirmed by a sweat chloride of 60 mmol/L or more.
Why it matters in the exam
Questions describe a newborn with meconium ileus, an infant failing to thrive with fatty stools and recurrent chest infections, a child with nasal polyps or rectal prolapse, or a man with infertility from congenital bilateral absence of the vas deferens. Almost always the question asks for the diagnostic test — the sweat test — and sometimes for the typical acid-base state: hypochloraemic metabolic alkalosis with hyponatraemia from salt loss in sweat.
A second point is the microbiology: S. aureus in early life, Pseudomonas aeruginosa (especially mucoid strains) later, Burkholderia cepacia complex predicting deterioration, and ABPA in a child with wheeze, very high IgE and migrating infiltrates. A first isolate of Pseudomonas is targeted for eradication with inhaled antibiotics.
In Israel CF is part of newborn screening (IRT combined with a mutation panel), and carrier testing is offered to couples. Treatment rests on airway clearance, dornase alfa and hypertonic saline, pancreatic enzymes, a high-calorie diet and vitamins A, D, E and K. CFTR modulators (elexacaftor/tezacaftor/ivacaftor) change the course of the disease in people with at least one F508del allele. From age 10, an annual OGTT screens for CF-related diabetes.
Key points
- CF is an autosomal recessive disease of CFTR.
- Sweat chloride of 60 mmol/L or more is diagnostic; 30–59 is the intermediate range.
- Pseudomonas and B. cepacia drive the course of lung disease.
- Pancreatic enzymes, a high-calorie diet and vitamins ADEK.
- CFTR modulators change the disease in people with F508del.
Summary table
| System | Manifestation | Work-up or clue | Treatment |
|---|---|---|---|
| Lungs | Chronic cough, bronchiectasis, recurrent infection | S. aureus, Pseudomonas, B. cepacia; ABPA | Airway clearance, dornase alfa, hypertonic saline, inhaled tobramycin |
| Pancreas and nutrition | Fatty stools, failure to thrive | Low faecal elastase | Pancreatic enzymes, high-calorie diet, vitamins ADEK |
| Bowel | Meconium ileus in the newborn; DIOS later in life | Obstruction at the terminal ileum | Contrast enema or surgery; laxatives |
| Salt and sweat | Hypochloraemic alkalosis, dehydration in heat | Low serum sodium and chloride | Salt supplements |
| Endocrine and liver | CF-related diabetes, cholestatic liver disease | Annual OGTT from age 10 | Insulin; ursodeoxycholic acid as needed |
| Fertility | Congenital bilateral absence of the vas deferens | Azoospermia | Assisted reproduction |
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Sources
- Cystic Fibrosis Foundation Consensus Guidelines for the Diagnosis of Cystic Fibrosis, 2017 — Sweat chloride thresholds and newborn screening
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Cystic Fibrosis
- ECFS Standards of Care for Cystic Fibrosis, 2024 update — CFTR modulators and multidisciplinary follow-up
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.