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What is cystic fibrosis?

Cystic Fibrosis (CF) is an inherited condition that mainly affects the lungs, pancreas, and sweat glands. It causes the production of thick, sticky mucus that leads to recurrent respiratory infections and blocks the release of pancreatic enzymes, inhibiting the digestion of protein and fat.

CF is one of the most common recessive genetic disorders in the U.S. A recessive disorder occurs when each of the two copies of a gene (one inherited from each parent) is abnormal. According to Cystic Fibrosis Foundation, it is estimated that 30,000 Americans are living with CF and approximately 1,000 new cases are diagnosed every year. Most people with CF are diagnosed in early childhood.

CF is caused by mutations (disease-causing variations in the DNA) in a gene called CFTR located on chromosome seven. More than 2,000 different CF mutations have been identified so far, but only a few are common. The majority of cystic fibrosis cases in the U.S. are caused by a mutation called deltaF508 (F508).

The CFTR gene is responsible for the normal production of a protein called cystic fibrosis transmembrane conductance regulator (CFTR). In CF, the CFTR protein may be dysfunctional or totally absent. With dysfunctional or absent CFTR, chloride does not move out of the ducts into surrounding fluid, resulting in the production of thick, sticky mucus. Since CFTR levels are usually highest in the epithelial cells lining the internal surfaces of the bronchi of the lungs, pancreas, sweat glands, salivary glands, intestine, and reproductive organs, these are the areas most affected by CF.

Most people with CF develop respiratory and pancreatic symptoms early in life, although the severity of signs and symptoms varies from person to person, even in those carrying the exact same mutations. The majority of adult men with CF are also infertile due to missing or underdeveloped vas deferens, the tubules that transport sperm from the testicles.

An individual with one normal CFTR gene copy and one abnormal gene copy is a CF carrier. Carriers do not generally have symptoms, but they may pass a copy of their abnormal gene on to their children. Both biological parents must either be carriers or have CF in order for their child to have CF.

The risk associated with carrying an abnormal CF gene can be generally associated with a person’s ethnic background. Caucasians from Northern Europe and Ashkenazi Jews have the highest incidence of CF with about 1 in 25 individuals being CF carriers.


About Cystic Fibrosis

Signs and Symptoms

Signs and symptoms associated with cystic fibrosis include:

  • Frequent coughing, chronic cough and sputum production
  • Repeated or persistent chest infections such as bronchitis or pneumonia
  • Recurrent sinus infections and nasal congestion caused by nasal polyps
  • Abdominal pain or discomfort
  • In newborns, lack of stool in the first 24-48 hours after birth (meconium ileus)
  • Chronic diarrhea or bulky, foul-smelling, greasy stools
  • Weight loss or malnutrition
  • In children, failure to gain weight or grow at a normal rate (failure to thrive)
  • Decreased levels of protein in the blood, leading to accumulation of fluid, usually just under the skin (edema)

CF interferes with electrolyte and fluid balance in the body. In most individuals affected with CF, sweat contains up to five times more salt (sodium chloride) than unaffected individuals. Losing excess sodium and chloride can affect the heart rhythm and may sometimes cause shock.

In people with CF, lubricating mucus in the lungs becomes thick and sticky, providing a breeding ground for microbes, causing frequent respiratory infections. These must be aggressively treated with intravenous, oral and/or inhaled antibiotics. Many of the illnesses associated with CF are due to respiratory infections and lung complications.

Mucus plugs in the pancreas lead to blocked ducts, resulting in malabsorption because pancreatic enzymes (needed to digest food, particularly protein and fat, so that it can be absorbed) cannot travel to the intestine. This can lead to vitamin deficiencies and malnutrition. Pancreatic enzyme and vitamin A, D, E and K supplements can ease these symptoms, along with a low-fat, high-protein diet. If pancreatic damage progresses, some people with CF eventually become diabetic.

Other problems associated with CF include:

  • Gallstones
  • Pancreatic insufficiency and pancreatitis
  • Delayed growth and delayed sexual development at puberty
  • Enlargement or rounding (clubbing) of the fingertips and toes
  • Chronic liver disease and biliary cirrhosis
  • Rectal prolapse (protrusion of the rectum through the anus)
  • Infertility in men


Laboratory tests may be used to screen for and help diagnose cystic fibrosis (CF), to determine whether someone is a genetic carrier of CF, and/or to evaluate a person with CF to help manage the condition.

Tests for screening and diagnosis:

Even when there is no family history of the disorder, the American College of Obstetricians and Gynecologists (ACOG) recommends that all couples planning a pregnancy or having their first visit for prenatal care be offered a carrier screening test for cystic fibrosis.

All newborn screening programs test babies for cystic fibrosis. The following can be used in testing for CF. Some states use only the IRT blood test, while others use IRT and CF gene mutation testing for screening. Positive screening results may be followed by sweat chloride testing for confirmation.

  • CF Gene Mutations Testing—this testing may be used to screen for CF or to determine whether someone is a CF carrier. The American College of Medical Genetics (ACMG) and ACOG recommend a panel of 23 of the most common CFTR mutations. This panel detects most carriers and cases of CF. Some laboratories offer expanded panels of up to 100 or more mutations. Less common mutations may not be detected. People who undergo CF gene mutation testing should receive genetic counseling to understand the implications of the results.
  • Immunoreactive Trypsinogen (IRT)—this is a blood test that measures the level of immunoreactive trypsinogen. Trypsinogen is produced in the pancreas and transported to the intestine, where it is activated to form the enzyme trypsin. In CF, thick mucus can obstruct pancreatic ducts and prevent trypsinogen from reaching the intestine. Blood IRT levels are elevated in people with CF, but positive results must be followed by confirmatory sweat chloride testing.
  • Sweat Chloride Test—this test involves measuring the chloride level in a sweat sample collected through a special procedure. The sweat of a person with CF may be up to five times saltier than normal. This test is considered the “gold standard” and is used to confirm positive newborn screening tests as well as to diagnose older children and adults.

Nasal (transepithelial) Potential Difference (NPD)—this test is used less frequently than those listed above. The procedure is technically very difficult to perform and is available at only a few CF centers around the country. For the test, an electrode is placed on the lining of the nose, which is then bathed with a series of fluids that contain different salts. The fluids change the flow of sodium and chloride (ions) across the nose lining, generating a potential difference (PD) that can be measured. The abnormal sodium and chloride transport in the nose lining of people with CF is associated with a different pattern of nasal PD compared to the nose lining of people without CF. Results of the NPD must be considered along with signs and symptoms as well as sweat chloride test and CF gene mutation results when diagnosing CF.

Several other tests may be used to help evaluate a person with CF. Examples include:

Non-laboratory tests that may be done include bone and chest X-rays, upper GI and small bowel series, and lung function tests. See RadiologyInfo.org to learn more about these.


Currently, there is no cure for cystic fibrosis, only treatments aimed at minimizing the severity of the symptoms and improving quality of life. Treatments are tailored for the individual and goals usually involve activities to loosen and remove excess mucus from the lungs, prevent lung infections and blockages in the digestive tract, and to provide adequate nutrition with specialized diets.

Some therapies may include exercise regimens and physical therapy as well as drugs such as antibiotics, anti-inflammatory medications, and bronchodilators.

Newer therapies called CTFR modulators have been developed. They may be used to correct the function of defective CTFR proteins. These modulators are effective only for CF patients with specific CF gene mutations. For more information, see the Cystic Fibrosis Foundation’s webpage on CFTR Modulator Therapies.

Some people with CF may undergo a lung transplant, which can allow them to live longer and improves their quality of life. Research is being conducted to develop a cure and to enhance treatments. Great strides have been made over the past ten years, which are allowing many people with CF to live longer with improvement in quality of life.

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