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For further information, see CMDT Part 9-09: Cystic Fibrosis

Key Features

Essentials of Diagnosis

  • Chronic or recurrent cough, sputum production, dyspnea, and wheezing

  • Recurrent airways infections or chronic colonization of the airways with

    • Haemophilus influenzae

    • Pseudomonas aeruginosa

    • Staphylococcus aureus

    • Burkholderia cenocepacia

  • Bronchiectasis and scarring on chest radiographs

  • Airflow obstruction on spirometry

  • Pancreatic insufficiency, recurrent pancreatitis, distal intestinal obstruction syndrome, chronic hepatic disease, nutritional deficiencies, or male urogenital abnormalities

  • Sweat chloride concentration > 60 mEq/L on two occasions

  • Mutations in genes known to cause cystic fibrosis

General Considerations

  • Most common fatal hereditary disorder of whites in the United States

  • Autosomal recessive disorder due to mutations affecting a membrane chloride channel (the cystic fibrosis transmembrane conductance regulator, or CFTR)

  • At least 1000 mutations to the CFTR gene are described, with " ΔF508" accounting for approximately 60% of cases

  • Pathophysiology results from production of an abnormal mucous in exocrine glands, which leads to tissue destruction and, in the respiratory tract, impairs mucociliary clearance

  • Variety of mutations is reflected in wide range of pulmonary and nonpulmonary manifestations


  • Affects 1 in 3200 whites; 1 in 25 is a carrier

Clinical Findings

Symptoms and Signs

  • Disease should be suspected in young adults with a history of chronic lung disease, pancreatitis, or infertility

  • Productive cough, decreased exercise tolerance, and recurrent hemoptysis are typical

  • Patients also often complain of chronic rhinosinusitis symptoms, steatorrhea, diarrhea, and abdominal pain

  • Patients with cystic fibrosis are often malnourished with low body mass index

  • Common extrapulmonary manifestations

    • Steatorrhea

    • Diarrhea

    • Abdominal pain

  • Nearly all male patients have congenital absence of the vas deferens with azoospermia

  • Other findings include

    • Digital clubbing

    • Increased anteroposterior chest diameter

    • Hyperresonance on percussion

    • Apical crackles

Differential Diagnosis

  • Chronic obstructive pulmonary disease

  • Asthma

  • Alpha-1-antiprotease deficiency

  • Bronchiolitis

  • Celiac disease

  • Chronic sinusitis


Laboratory Tests

  • Arterial blood gases reveal hypoxemia, with compensated respiratory acidosis in advanced disease

  • Pulmonary function tests

    • A mixed obstructive and restrictive pattern

    • Reduced FVC, airflow rates, and total lung capacity

    • Air trapping and reduced diffusion capacity are common

  • Genotyping, measurement of nasal membrane potential difference, semen analysis, or assessment of pancreatic function can play a role in diagnosis

  • Sputum cultures

    • Frequently show S aureus and P aeruginosa

    • Occasionally show H influenzae, S maltophilia, and B cenocepacia

Imaging Studies

  • Hyperinflation is seen early on chest radiographs

  • Peribronchial cuffing, mucus plugging, bronchiectasis, atelectasis, small rounded peripheral opacities, and increased interstitial markings are common

  • High-resolution CT is the test of choice to confirm bronchiectasis

Diagnostic Procedures

  • Chloride sweat test reveals elevated sodium and chloride levels; two tests on different ...

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