Definition and epidemiology
Cystic fibrosis is a life-threatening autosomal recessive genetic disorder characterized by dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. This results in abnormal chloride and water transport across epithelial surfaces, producing thick, viscous secretions in multiple organ systems, particularly the lungs and pancreas.
CF is the most common fatal genetic disease among Caucasians, with an incidence of approximately 1 in 3,500 live births in populations of Northern European ancestry. The carrier frequency in this population is approximately 1 in 25. The disease is less common in African Americans (1 in 15,000), Asian Americans (1 in 31,000), and Hispanic Americans (1 in 9,000).
With advances in treatment, median survival has improved dramatically from less than one year in the 1950s to approximately 45-50 years today in developed countries. More than half of individuals with CF are now adults. Males and females are equally affected, though male infertility due to congenital bilateral absence of the vas deferens is nearly universal.
- CF is autosomal recessive; ΔF508 is the most common mutation (70% of alleles).
- Sweat chloride >60 mmol/L on two occasions confirms diagnosis.
- Meconium ileus in a newborn is pathognomonic for CF until proven otherwise.
- Chronic Pseudomonas aeruginosa infection is the hallmark of CF lung disease.
- Pancreatic insufficiency causes steatorrhea and fat-soluble vitamin deficiencies (A, D, E, K).
- More than 95% of males with CF are infertile due to congenital bilateral absence of the vas deferens.
- Elexacaftor/tezacaftor/ivacaftor (triple therapy) dramatically improves outcomes for patients with at least one F508del mutation.
- Newborn screening uses immunoreactive trypsinogen (IRT) followed by genetic testing and sweat chloride confirmation.
Etiology and risk factors
CF is caused by mutations in the CFTR gene located on chromosome 7. More than 2,000 mutations have been identified, classified into six functional classes based on their effect on CFTR protein production, processing, gating, conductance, abundance, or stability.
Delta F508 (ΔF508) is the most common mutation worldwide, accounting for approximately 70% of CF alleles in Northern European populations. It results in misfolding and degradation of the CFTR protein before it reaches the cell membrane. Other common mutations include G542X, G551D, N1303K, and W1282X.
The severity of disease correlates somewhat with genotype. Patients with two severe mutations (class I-III) typically develop pancreatic insufficiency, while those with at least one mild mutation may retain pancreatic function. However, pulmonary disease severity is more variable and influenced by modifier genes, environmental factors, and infections.
Risk factors
- Family history: Each child of two carrier parents has a 25% chance of having CF
- Ethnicity: Highest risk in Northern European, Ashkenazi Jewish populations
- Consanguinity: Increases risk of homozygous mutations
Newborn screening programs in many countries now identify most cases before symptom onset through immunoreactive trypsinogen (IRT) testing followed by genetic analysis.
Pathophysiology
The CFTR protein normally functions as a chloride channel in epithelial cells. In CF, defective CFTR leads to decreased chloride secretion and increased sodium reabsorption, resulting in dehydrated, thick secretions on epithelial surfaces.
Respiratory system
Thick mucus in airways impairs mucociliary clearance, creating an environment prone to chronic bacterial colonization and infection. The inflammatory response to infection causes progressive bronchiectasis, airway remodeling, and eventual respiratory failure. Pseudomonas aeruginosa is the most significant pathogen in CF lung disease, with chronic colonization associated with accelerated lung function decline. Other common organisms include Staphylococcus aureus (including MRSA), Haemophilus influenzae, Burkholderia cepacia complex, and nontuberculous mycobacteria. Aspergillus fumigatus can cause allergic bronchopulmonary aspergillosis (ABPA) in susceptible patients.
Pancreas
Thick secretions obstruct pancreatic ducts, leading to autodigestion and fibrosis. Approximately 85-90% of CF patients develop exocrine pancreatic insufficiency, resulting in malabsorption of fats and fat-soluble vitamins (A, D, E, K). Endocrine insufficiency develops in approximately 50% of adults, causing CF-related diabetes (CFRD).
Gastrointestinal system
Newborns may present with meconium ileus (10-20% of cases). Older patients can develop distal intestinal obstruction syndrome (DIOS). Inspissated secretions in bile ducts can lead to biliary cirrhosis and portal hypertension.
Reproductive system
More than 95% of males have congenital bilateral absence of the vas deferens (CBAVD), causing obstructive azoospermia. Females have reduced fertility due to thick cervical mucus but can conceive.
Clinical features
Clinical presentation varies based on age at diagnosis, genotype, and organ involvement.
Neonatal and infant presentation
- Meconium ileus: Failure to pass meconium within 24-48 hours, abdominal distention (pathognomonic finding)
- Failure to thrive: Poor weight gain despite adequate caloric intake
- Steatorrhea: Frequent, bulky, foul-smelling, greasy stools
- Prolonged neonatal jaundice: Due to inspissated bile
- Hypoproteinemia and edema: From malabsorption
- Rectal prolapse: From frequent bulky stools and malnutrition
Respiratory manifestations
- Chronic cough: Productive cough, often with purulent sputum
- Recurrent pneumonia: Particularly with typical CF pathogens
- Wheezing and dyspnea: From airway obstruction and bronchospasm
- Hemoptysis: From bronchiectasis and inflammation
- Digital clubbing: Develops with chronic hypoxia
- Nasal polyps and chronic sinusitis: Common in children and adults
Gastrointestinal manifestations
- Pancreatic insufficiency: Steatorrhea, fat-soluble vitamin deficiencies
- Recurrent pancreatitis: In patients with residual pancreatic function
- DIOS: Crampy abdominal pain, palpable mass in right lower quadrant
- CF-related liver disease: Hepatomegaly, portal hypertension, varices
- Gastroesophageal reflux: Common and can worsen lung disease
Other manifestations
- Salty-tasting skin: Classic finding noticed by parents when kissing infant
- Male infertility: CBAVD in nearly all males
- CF-related diabetes: Typically develops in adolescence or adulthood
- Osteoporosis: From vitamin D deficiency, inflammation, glucocorticoid use
- Arthropathy: CF-related arthritis, hypertrophic osteoarthropathy
Diagnosis
Diagnosis requires clinical features consistent with CF plus evidence of CFTR dysfunction through sweat testing or genetic analysis.
Sweat chloride test
The quantitative pilocarpine iontophoresis sweat test remains the gold standard. Pilocarpine stimulates sweat production, which is collected and analyzed for chloride concentration.
Interpretation:
- >60 mmol/L: Diagnostic of CF (must be confirmed on two occasions)
- 40-59 mmol/L: Intermediate, requires further evaluation
- <40 mmol/L: CF unlikely
The test should be performed at accredited centers using standardized methods. False negatives can occur with edema, hypoproteinemia, or technical errors. At least 75 mg of sweat is needed for accurate analysis.
Genetic testing
CFTR gene sequencing identifies disease-causing mutations. Standard panels test for the most common mutations, but expanded sequencing may be needed if clinical suspicion is high with negative results. Identification of two disease-causing mutations confirms the diagnosis.
Newborn screening
Most developed countries perform newborn screening using:
- Immunoreactive trypsinogen (IRT): Elevated in CF due to pancreatic inflammation
- DNA analysis: If IRT is elevated, genetic testing for common mutations
- Sweat test: To confirm positive screens
Additional diagnostic tests
- Chest X-ray: Hyperinflation, bronchiectasis, mucus plugging, infiltrates
- High-resolution CT: Demonstrates bronchiectasis, mucus plugging, tree-in-bud opacities
- Pulmonary function tests: Obstructive pattern with reduced FEV1 and FEV1/FVC ratio
- Sputum culture: Identifies pathogens for targeted antibiotic therapy
- Fecal elastase: <200 mcg/g indicates pancreatic insufficiency
- 72-hour fecal fat: Confirms steatorrhea
- Nasal potential difference or intestinal current measurement: Functional tests when diagnosis is unclear
Diagnostic criteria
CF diagnosis requires:
- One or more characteristic clinical features (chronic sinopulmonary disease, GI/nutritional abnormalities, salt loss syndromes, male urogenital abnormalities)
PLUS evidence of CFTR dysfunction:
- Sweat chloride ≥60 mmol/L on two occasions, OR
- Two disease-causing CFTR mutations, OR
- Abnormal nasal potential difference
Differential diagnosis
Several conditions can mimic CF, particularly in patients with atypical presentations or single-organ involvement.
Respiratory presentations
- Primary ciliary dyskinesia: Chronic sinusitis, bronchiectasis, situs inversus (Kartagener syndrome), but normal sweat test
- Immunodeficiency disorders: Recurrent infections but without pancreatic involvement or elevated sweat chloride
- Severe asthma: Wheezing and cough, but responsive to bronchodilators, normal sweat test
- Bronchiectasis from other causes: Tuberculosis, allergic bronchopulmonary aspergillosis, post-infectious
Gastrointestinal presentations
- Celiac disease: Malabsorption, steatorrhea, failure to thrive; positive serology, villous atrophy
- Shwachman-Diamond syndrome: Pancreatic insufficiency with neutropenia, skeletal abnormalities, bone marrow dysfunction
- Chronic pancreatitis: Recurrent pancreatitis but without respiratory manifestations
- Intestinal malrotation: Presents with obstruction in newborns
Combined features
- CFTR-related metabolic syndrome (CRMS): Abnormal newborn screen but sweat chloride <30 mmol/L, uncertain clinical significance
- CFTR-related disorder: Intermediate sweat chloride (30-59 mmol/L) or single CFTR mutation with milder, single-organ manifestations
Management
CF management is multidisciplinary, focusing on maintaining lung function, optimizing nutrition, preventing and treating infections, and addressing complications. Care is best delivered at specialized CF centers.
Airway clearance and pulmonary management
Airway clearance therapy is the cornerstone of CF care, performed 1-3 times daily. Techniques include chest physiotherapy, positive expiratory pressure (PEP) devices, high-frequency chest wall oscillation vests, and exercise.
Mucolytics:
- Dornase alfa (recombinant DNase): Breaks down extracellular DNA in mucus, improving clearance
- Hypertonic saline: Hydrates airway surface liquid, improves mucociliary clearance
Bronchodilators (albuterol, ipratropium) are used before airway clearance to open airways.
Infection management
Antibiotic therapy is tailored to sputum culture results:
- Acute exacerbations: Aggressive IV antibiotic therapy (typically 14 days) targeting identified pathogens; often requires two agents for Pseudomonas
- Chronic suppressive therapy: Inhaled antibiotics (tobramycin, aztreonam, colistin) for chronic Pseudomonas colonization
- Early eradication: Aggressive treatment of first Pseudomonas isolation to prevent chronic infection
- Prophylaxis: Some centers use continuous oral antistaphylococcal antibiotics in young children
Anti-inflammatory therapy:
- Azithromycin: Immunomodulatory effects, improves lung function in chronic Pseudomonas infection
- Ibuprofen: High-dose therapy slows lung function decline in children (requires monitoring)
- Systemic corticosteroids: Reserved for ABPA and severe exacerbations
CFTR modulator therapy
CFTR modulators represent a major advancement, targeting the underlying defect:
- Ivacaftor: Potentiator for gating mutations (G551D and others), improves chloride transport
- Lumacaftor/ivacaftor, tezacaftor/ivacaftor: Corrector/potentiator combinations for F508del homozygotes
- Elexacaftor/tezacaftor/ivacaftor: Highly effective triple combination for at least one F508del mutation, dramatically improves lung function and quality of life
These therapies are mutation-specific and have transformed prognosis for eligible patients.
Nutritional management
Pancreatic enzyme replacement therapy (PERT) with lipase, protease, and amylase is essential for patients with pancreatic insufficiency, taken with all meals and snacks.
High-calorie diet: 120-150% of recommended daily allowance due to increased energy expenditure and malabsorption.
Fat-soluble vitamin supplementation (A, D, E, K) is required, with monitoring of serum levels.
Nutritional support: Nasogastric or gastrostomy tube feeding may be needed for severe malnutrition.
Management of complications
- CF-related diabetes: Insulin therapy is first-line; oral agents are generally ineffective
- DIOS: Polyethylene glycol, enemas, lactulose; surgery if conservative measures fail
- Hemoptysis: Antibiotics for infection; consider embolization for massive bleeding
- Pneumothorax: Chest tube drainage; pleurodesis or surgery for recurrence
- Liver disease: Ursodeoxycholic acid may slow progression; transplant for end-stage disease
- Osteoporosis: Calcium, vitamin D, bisphosphonates
Transplantation
Lung transplantation is considered for end-stage lung disease (FEV1 <30% predicted, frequent exacerbations, refractory pneumothorax, massive hemoptysis). Five-year survival post-transplant is approximately 50-60%. Liver and pancreas transplantation may be needed for respective organ failure.
Psychosocial support
Comprehensive care includes mental health support, genetic counseling, fertility counseling, and transition planning from pediatric to adult care.
Complications and prognosis
Pulmonary complications
- Progressive bronchiectasis: Leading cause of morbidity and mortality
- Respiratory failure: Requires oxygen therapy, noninvasive ventilation, or transplantation
- Hemoptysis: Occurs in 60% of adults; can be life-threatening
- Pneumothorax: Occurs in 3-4% annually in adults with advanced disease
- Allergic bronchopulmonary aspergillosis: Develops in 5-10% of patients
- Cor pulmonale: Right heart failure from chronic hypoxia
Gastrointestinal complications
- DIOS: Occurs in 15-20% of patients
- Rectal prolapse: More common in children
- Cirrhosis and portal hypertension: Develops in 5-10% of adults
- CF-related diabetes: Occurs in up to 50% of adults
- Cholecystitis and cholelithiasis: Increased risk
- GI malignancies: Slightly increased risk, particularly colorectal cancer
Other complications
- Male infertility: Nearly universal (>95%)
- Reduced female fertility: Approximately 20% conceive naturally
- Osteoporosis and pathologic fractures: Common in adults
- Arthropathy: CF-related arthritis, hypertrophic osteoarthropathy
- Nephrolithiasis: From dehydration and hyperoxaluria
- Salt depletion: During heat exposure or exercise
Prognosis
Prognosis has improved dramatically over recent decades. Median predicted survival for children born today with CF in developed countries exceeds 50 years, with CFTR modulators expected to further extend life expectancy.
Prognostic factors:
Favorable:
- Diagnosis through newborn screening (earlier treatment)
- Pancreatic sufficiency
- Male sex
- Milder genotypes
- Access to CFTR modulator therapy
- Higher socioeconomic status and specialized center care
Unfavorable:
- Low FEV1 (<30% predicted)
- Chronic Pseudomonas or Burkholderia infection
- CF-related diabetes
- Frequent pulmonary exacerbations
- Low BMI and poor nutritional status
- Massive hemoptysis or pneumothorax
- Female sex
Respiratory failure remains the leading cause of death (>90% of mortality). With optimal care at specialized centers and access to CFTR modulators, many patients now live well into adulthood with good quality of life. The introduction of highly effective modulator therapy has fundamentally changed the disease trajectory for a majority of patients.
CFTR for manifestations: Chronic cough/Clubbing, Failure to thrive, Trypsinogen elevated (newborn screen), Recurrent infections (Pseudomonas). PANCREAS for features: Pseudomonas, Absence of vas deferens, Nasal polyps, Chronic cough, Rectal prolapse, Elevated sweat chloride, Azospermia, Steatorrhea.
Practice questions
1. A 3-month-old infant is brought to the clinic for poor weight gain. She was born at term without complications but has had difficulty gaining weight despite feeding well. The parents report frequent, foul-smelling, greasy stools. On examination, the infant appears malnourished with a distended abdomen. A sweat chloride test is ordered and returns at 68 mmol/L. Which organism is this patient at highest risk for chronic pulmonary colonization later in life?
2. A 28-year-old man with cystic fibrosis presents to the emergency department with sudden-onset right-sided chest pain and dyspnea. He has a chronic productive cough and is on inhaled tobramycin and dornase alfa. Vital signs show BP 118/72 mmHg, HR 102 bpm, RR 24/min, O2 saturation 88% on room air. Physical examination reveals decreased breath sounds on the right side with hyperresonance to percussion. What is the most likely diagnosis?
3. A newborn is noted to have abdominal distention and has not passed meconium 36 hours after birth. Abdominal X-ray shows dilated loops of bowel with a ground-glass appearance in the right lower quadrant. The infant's mother had polyhydramnios during pregnancy. Which additional finding would most strongly support the suspected diagnosis?
Frequently asked questions
What causes cystic fibrosis?
Cystic fibrosis is caused by mutations in the CFTR gene on chromosome 7, inherited in an autosomal recessive pattern. The most common mutation is ΔF508 (delta F508), accounting for approximately 70% of CF alleles worldwide. More than 2,000 different CFTR mutations have been identified. These mutations result in defective chloride channels in epithelial cells, leading to thick, viscous secretions in multiple organs. Both parents must be carriers for a child to be affected, with a 25% risk in each pregnancy when both parents carry a mutation.
What are the first symptoms of cystic fibrosis?
The first symptoms depend on age at diagnosis. In newborns, meconium ileus (failure to pass stool in the first 24-48 hours) or prolonged jaundice may be presenting signs. In infants, failure to thrive despite good appetite, frequent bulky foul-smelling stools (steatorrhea), and recurrent respiratory infections are typical. Parents may notice salty-tasting skin when kissing the baby. Some children present later with chronic cough, recurrent pneumonia, nasal polyps, or rectal prolapse. Today, most cases are identified through newborn screening programs before symptoms develop.
How is cystic fibrosis diagnosed?
Diagnosis requires clinical features consistent with CF plus evidence of CFTR dysfunction. The quantitative pilocarpine iontophoresis sweat test is the gold standard; a sweat chloride level greater than 60 mmol/L on two separate occasions confirms the diagnosis. Genetic testing identifying two disease-causing CFTR mutations also confirms CF. Most cases today are first identified through newborn screening using immunoreactive trypsinogen (IRT), followed by DNA analysis and confirmatory sweat testing. Additional tests like chest X-ray, pulmonary function tests, and fecal elastase help assess organ involvement.
Is cystic fibrosis curable?
Cystic fibrosis currently has no cure, but treatment has advanced dramatically. CFTR modulator therapies (particularly elexacaftor/tezacaftor/ivacaftor) target the underlying genetic defect in eligible patients and significantly improve lung function, nutritional status, and quality of life, though they do not cure the disease. Standard management includes airway clearance, pancreatic enzyme replacement, antibiotics, nutritional support, and anti-inflammatory medications. Lung transplantation is an option for end-stage lung disease but replaces rather than cures diseased lungs. With comprehensive care, median survival now exceeds 45-50 years, and many patients live productive lives into adulthood.
Cystic fibrosis vs chronic bronchitis — what is the difference?
Cystic fibrosis is a genetic disorder caused by CFTR mutations, while chronic bronchitis is typically acquired from smoking or environmental exposures. CF presents in childhood with multi-organ involvement (pancreatic insufficiency, malabsorption, sinusitis, male infertility) and specific pathogens like Pseudomonas aeruginosa. Chronic bronchitis presents in adults with productive cough for at least three months per year over two consecutive years, usually associated with smoking. CF diagnosis requires elevated sweat chloride or genetic testing, while chronic bronchitis is a clinical diagnosis. Treatment differs fundamentally: CF requires specialized multidisciplinary care with enzyme replacement and genetic-targeted therapies, while chronic bronchitis focuses on smoking cessation and bronchodilators.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: E84
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.