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Cystic Fibrosis: How CF Affects the Body

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This information was reviewed and approved by Sara Brayshaw, RN, MSN (10/1/2019).

When the CFTR gene is defective, many organ systems are affected. While damage to the lungs and pancreas is the most critical, CF can involve other organ systems and greatly impact the lives of people with CF.

Lung Disease

Cystic fibrosis lung disease primarily involves the small and medium-sized airways of the lungs, called bronchi. Very early in life, increased inflammation and mucous production starts to block the smallest bronchi. Blocked bronchi become dilated. This dilation, called bronchiectasis, causes permanent damage to the lungs. Bronchiectatic airways can become plugged with mucous and become a place where bacteria can take hold. Often the bacteria are not affected by either antibiotics or the immune system. One of the classic features of CF is that the upper lobes of the lungs are typically the sites of greatest damage.

The vast majority of cystic fibrosis patients die of respiratory failure, so preserving lung function is a main goal of treatment. The extent of lung disease is measured by a pulmonary function test called the FEV1. This test measures the volume of air an individual can forcibly exhale in one second. In addition to being the primary marker of disease severity, FEV1 is often the principal measure used to judge the success of new treatments.


Pulmonary Exacerbations

When lung symptoms get worse, it’s called a pulmonary exacerbation. Most people with CF will have less than one exacerbation per year, but with advancing lung disease, the frequency typically increases.

Symptoms of Pulmonary Exacerbation

  • Increased cough
  • Increased sputum production
  • Change in sputum appearance (darker or blood streaked)
  • Coughing up blood (hemoptysis)
  • Increased shortness of breath
  • Decreased appetite
  • Weight loss
  • Inability to attend school or work
  • Weakness and fatigue

Exacerbations are partly caused by increased growth of the bacteria that chronically infect the airways. For people with cystic fibrosis, exacerbations begin following symptoms of a viral upper respiratory tract infection. Sometimes, symptoms will come on gradually over the course of weeks or months.


Other Lung Complications

Many people with CF have a degree of airway bronchospasm that resembles asthma. In these individuals, respiratory symptoms and lung function are improved through the use of bronchodilators. Patients with more advanced lung disease are at risk for complications such as bleeding into the airways (hemoptysis).

Coughing up blood is a common feature of increased infection, and usually is resolved with antibiotics. More severe complications include collapse of lobes, or leaking of air outside of the lungs (pneumothorax). These complications are associated with advanced lung disease and can be a cause of sudden worsening of respiratory symptoms. Urgent medical evaluation and treatment are required.



Like the bronchi, the small ducts of the pancreas are also obstructed by thick secretions. Nearly 90 percent of people with cystic fibrosis can’t excrete sufficient pancreatic enzymes or bicarbonate into the duodenum (small intestine). This greatly reduces the capacity to metabolize and absorb dietary fats and proteins. Carbohydrate absorption can also be impaired.

Symptoms include greasy and foul-smelling diarrhea, abdominal pain, failure to gain weight and malnutrition. Historically, children with CF died in early childhood as a result of pancreatic insufficiency, before the lung manifestation of the disease became severe. Development of pancreatic replacement enzymes and other nutritional supplements has significantly reduced the complications associated with pancreatic insufficiency.


CF-Related Diabetes

Insulin is produced within the pancreas. Most children with cystic fibrosis are still capable of producing sufficient insulin. Increasing numbers of adult men and women with CF will require supplemental insulin. This CF-related diabetes (CFRD) is distinct from the Type I or Type II diabetes that are encountered in the general population. Often the symptoms of CFRD are quite subtle, and can include weight loss or inability to regain weight after an exacerbation, as well as unexpectedly rapid decline in lung function. Administration of insulin is nearly always associated with improved weight gain and lung function.



At birth, up to 20 percent of CF patients will have an obstruction of the bowel. Many individuals with cystic fibrosis experience difficulty with constipation throughout life. CF can make thick mucus in the intestines. This mucus without enough fluid can cause constipation or lead to a bowel obstruction. Drink plenty of fluids and follow your care team's plan for treating hard stools, constipation and blockages.


Sinus Disease

Inflammation and infection of the upper airways and sinuses are extremely common in people with cystic fibrosis. Symptoms include runny nose, recurrent or chronic sinusitis, postnasal drip or nasal polyps. Aggressive medical treatment of CF sinus disease is very important. Poorly controlled sinusitis can greatly worsen the severity of CF lung disease and impact quality of life. Although sinus surgery is sometimes needed, this should only be performed by an otolaryngologist (ear, nose and throat (ENT) specialist) experienced in the treatment of cystic fibrosis-related sinus disease.



More than 98 percent of men with CF do not produce sperm. Infertility in men with cystic fibrosis is due to obstruction of the reproductive tract. In particular, damage to the vas deferens duct, which occurs prior to birth, results in a condition termed congenital bilateral absence of the vas deferens (CBAVD). However, when the obstruction is bypassed by directly aspirating the sperm from the epididymis, the sperm is generally found to be normal. There are techniques available to harvest sperm for men with CF who wish to father children.

Women with cystic fibrosis generally have normal reproductive anatomy and pregnancies followed by uncomplicated deliveries. Aspects of the female reproductive system can be altered by CF, malnutrition, delayed menarche (first menstrual period) and overall poor health contribute to decreased fertility. All women with cystic fibrosis should be considered capable of childbirth, and appropriate birth control should be considered to prevent unplanned pregnancies. Many CF-related treatments, including certain classes of antibiotics, are not recommended during pregnancy, or have unknown consequence. Thus pregnancy testing should be considered before initiating treatment with such medications.

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