Cystic fibrosis – Diagnostics – Overview of Information and Clinical Research

Finding out whether you or your child has cystic fibrosis involves several important tests that help doctors understand what’s happening inside the body. Early detection through newborn screening and follow-up diagnostic tests can make a significant difference in managing this genetic condition throughout life.

Introduction: Who Should Undergo Diagnostics

Cystic fibrosis diagnostics are important for several groups of people. First, all newborns in many countries are now screened for this condition as part of routine newborn screening programs, which are tests performed shortly after birth to check for certain serious health conditions. This early testing happens before any symptoms appear and gives families the best chance to start treatment early.^[1]

Beyond newborns, older children and adults should seek diagnostic testing if they experience certain warning signs. If someone has a persistent cough that produces mucus, frequent lung infections like pneumonia or bronchitis, wheezing and shortness of breath, or trouble gaining weight despite eating well, these symptoms warrant a visit to the doctor. Digestive problems are also common red flags, including loose or oily stools that are difficult to flush, stomach pain and bloating, or constipation.^[3]

Parents should be particularly attentive if their child has very salty-tasting skin, which can leave small crystals of salt visible on the skin. This is a classic sign of cystic fibrosis that has been recognized for centuries. Children who are not growing as quickly as expected or who have swollen fingertips with rounder nails should also be evaluated.^[3]

⚠️ Important

If you are pregnant or planning a pregnancy and someone in your or your partner’s family has cystic fibrosis, it is advisable to seek genetic counseling. This specialist can explain your risk of having a child with the condition and discuss testing options available to you.

People who have a family history of cystic fibrosis should also consider testing, even without symptoms. If a relative has been diagnosed with the condition or is known to carry the altered gene, you can arrange carrier testing to find out if you carry the gene mutation. This is especially important for couples planning to have children, as both parents must carry a mutated gene for their child to develop cystic fibrosis.^[12]

Diagnostic Methods

The diagnosis of cystic fibrosis relies on several different tests that work together to give doctors a complete picture. The most important and reliable test is called the sweat chloride test, which measures the amount of salt in a person’s sweat. People with cystic fibrosis have unusually high levels of salt in their sweat because the disease affects how the body moves salt and water in and out of cells.^[7]

The sweat test is straightforward and painless. A small area of skin, usually on the arm or leg, is stimulated with a chemical and a mild electrical current to produce sweat. The sweat is then collected on special paper or in a small tube and sent to a laboratory for analysis. This test is so reliable that it has been used for decades to diagnose cystic fibrosis. If the test shows high salt levels, it strongly suggests the person has the condition.^[11]

Genetic testing is another crucial diagnostic tool. This type of test looks at your DNA to find changes or mutations in the CFTR gene, which is the gene responsible for cystic fibrosis. More than 2,000 different mutations in this gene have been discovered, and different mutations can lead to different levels of disease severity. A blood sample is taken and analyzed in a specialized laboratory that can identify these genetic changes.^[6]

For newborns, the initial screening is done through a newborn blood spot test. A few drops of blood are taken from the baby’s heel shortly after birth and tested for a substance called immunoreactive trypsinogen, or IRT. This substance is a protein produced by the pancreas, and babies with cystic fibrosis often have elevated levels. However, a positive newborn screening result does not automatically mean the baby has cystic fibrosis, as IRT can be elevated for other reasons, including premature birth. That’s why babies with positive screening results need follow-up testing with a sweat test to confirm or rule out the diagnosis.^[7]

⚠️ Important

Most babies who have a positive newborn screening test do not actually have cystic fibrosis. The screening test is designed to catch all possible cases, which means some babies will test positive even though they do not have the disease. Only the sweat test can confirm the diagnosis.

Blood tests can also check for gene mutations directly. Some states and countries include genetic mutation testing as part of the newborn screening process. If one mutation is found, it means the baby could be a carrier or might have the disease, depending on whether mutations are present in both copies of the gene. People with only one mutated gene are called carriers—they don’t have symptoms of cystic fibrosis themselves but can pass the mutation to their children.^[7]

For people with digestive symptoms, additional tests may be performed to assess how well the pancreas is working. These include stool tests that check for the presence of digestive enzymes or look at the fat content in stool. People with cystic fibrosis often have trouble digesting fats because thick mucus blocks the tubes that carry digestive enzymes from the pancreas to the intestines. Tests like stool elastase or chymotrypsin measure enzymes that should be present if the pancreas is functioning normally.^[5]

Imaging tests such as chest X-rays can help doctors see if there is lung damage or signs of infection. While X-rays don’t diagnose cystic fibrosis on their own, they are useful for understanding how the disease is affecting the lungs over time. More advanced imaging like CT scans may be used to get detailed pictures of the lungs and check for complications like bronchiectasis, which is a condition where the airways become damaged and widened.^[3]

Lung function tests, also called pulmonary function tests, measure how well the lungs are working. During these tests, you breathe into a special machine that records how much air you can breathe in and out, and how fast you can do it. These tests are important for monitoring the progression of lung disease in people with cystic fibrosis, though they are used more for tracking the condition over time rather than for initial diagnosis.^[14]

Sometimes doctors need to examine the airways directly using a procedure called bronchoscopy. A thin, flexible tube with a camera on the end is inserted through the nose or mouth and down into the lungs. This allows the doctor to see the inside of the airways and collect samples of mucus for testing. Bronchoscopy is not routinely used for diagnosis but can be helpful in certain situations, such as when doctors need to identify specific bacteria causing lung infections.^[13]

For adults who develop symptoms later in life, the diagnostic process is similar but may take longer because cystic fibrosis is not always the first condition doctors think of. Some adults have a milder form called atypical cystic fibrosis, where symptoms affect only one organ or come and go over time. These individuals still need the sweat test and genetic testing to confirm the diagnosis.^[3]

Diagnostics for Clinical Trial Qualification

When people with cystic fibrosis want to participate in clinical trials—research studies testing new treatments—they must undergo specific diagnostic tests to determine if they are eligible. Clinical trials have strict criteria about who can participate, and these criteria are designed to ensure the safety of participants and the accuracy of the study results.^[5]

The most basic requirement for most cystic fibrosis clinical trials is confirmed diagnosis through genetic testing. Researchers need to know exactly which mutations in the CFTR gene a participant has because many new treatments are designed to work only with specific mutations. For example, some newer medications called CFTR modulators are designed to help the defective protein work better, but they only work for people with certain types of mutations. Before enrolling in such trials, participants must have detailed genetic testing to identify their specific mutations.^[6]

Lung function testing is almost always required for clinical trial enrollment. Researchers measure something called forced expiratory volume, or FEV1, which tells them how much air a person can forcefully breathe out in one second. This measurement is expressed as a percentage of what is expected for someone of the same age, height, and sex. Different clinical trials have different requirements—some may only accept participants with mild lung disease (higher FEV1 percentages), while others may focus on people with more advanced disease.^[8]

Blood tests are routinely performed before clinical trial enrollment to check overall health. These tests look at liver function, kidney function, blood cell counts, and electrolyte levels. Because cystic fibrosis can affect many organs, researchers need to make sure participants don’t have other health problems that could interfere with the study or put them at risk. Some trials exclude people with certain liver or kidney problems, while others specifically study people with these complications.^[14]

Sputum testing, which involves analyzing the mucus coughed up from the lungs, is another common requirement. This test identifies which bacteria are present in the lungs. Some clinical trials specifically look for people infected with certain bacteria like Pseudomonas aeruginosa or Staphylococcus aureus, while others may exclude people with certain infections. Knowing what bacteria are in the lungs helps researchers understand if a new treatment is working to reduce infections.^[13]

Weight and nutritional status are also assessed before clinical trial participation. Many trials require participants to have a body mass index (BMI) within a certain range. This is important because nutrition affects overall health and how well people respond to treatment. Some trials may require participants to have stable weight or to be taking pancreatic enzyme supplements if they have digestive problems.^[8]

Imaging studies such as chest X-rays or CT scans are often performed as part of the screening process for clinical trials. These images provide a baseline picture of lung structure and help researchers track changes over time. If the trial is testing a treatment meant to improve lung structure or reduce inflammation, having these images before treatment starts is essential for measuring whether the treatment is working.^[13]

For trials testing new CFTR modulator drugs, special tests may be done to measure how well the CFTR protein is functioning. One such test is called nasal potential difference measurement, which measures electrical differences across the lining of the nose. This test can show whether the CFTR protein is moving chloride ions properly. Another test measures the amount of chloride in sweat, similar to the diagnostic sweat test but used to track changes during treatment.^[6]

Age is also a factor in clinical trial eligibility, though this is not a diagnostic test but rather a basic criterion. Some trials are designed specifically for children, others for adults, and some for both. Clinical trial teams need accurate birth records and identification to ensure participants meet the age requirements.^[8]

Finally, participants in clinical trials must undergo regular follow-up testing throughout the study. This includes repeated lung function tests, blood tests, imaging studies, and other measurements to track how they are responding to the treatment being tested. These ongoing assessments are crucial for determining whether a new treatment is safe and effective.^[5]

Prognosis and Survival Rate

Prognosis

The outlook for people with cystic fibrosis has improved dramatically over recent decades. While cystic fibrosis remains a serious, lifelong condition that gets more severe over time, advances in treatment have made it possible for many people to live longer and healthier lives than ever before. The prognosis depends on several factors, including when the diagnosis is made, how quickly treatment begins, which gene mutations are present, and how well the lungs and other organs are functioning.^[2]

Early diagnosis through newborn screening gives children the best chance for a good outcome because treatment can start before serious lung damage occurs. People who are diagnosed later in life or who have the milder atypical form of cystic fibrosis may have a better prognosis initially, though they still need careful monitoring and treatment. The severity of symptoms can vary widely—some people have few problems and mild disease, while others experience severe complications affecting the lungs, digestive system, and other organs.^[3]

The most serious complications of cystic fibrosis involve the respiratory system. Repeated lung infections can cause progressive lung damage, leading to a condition called bronchiectasis where the airways become permanently damaged and widened. Over time, lung function declines, making it harder to breathe and reducing the amount of oxygen that reaches the body. Some people eventually develop end-stage lung disease, which is the most common cause of death in cystic fibrosis. However, lung transplantation is an option for people with severe lung disease and can significantly extend survival.^[14]

Other complications that affect prognosis include cystic fibrosis-related diabetes, which develops in many adults with the condition due to damage to the pancreas. Liver disease, pancreatitis, malnutrition, and osteoporosis can also occur and impact quality of life. Frequent monitoring and treatment of these complications can help prevent them from becoming severe.^[14]

Quality of life for people with cystic fibrosis has improved substantially. With proper management including airway clearance techniques, medications, nutritional support, exercise, and infection control, many people with cystic fibrosis can attend school, work, have relationships, and pursue their goals. The availability of new treatments, particularly CFTR modulator drugs that address the underlying protein defect, has been life-changing for many patients, improving lung function and reducing symptoms.^[6]

Survival rate

Survival rates for people with cystic fibrosis have increased dramatically over the past several decades. In the past, most children with cystic fibrosis died in early childhood, but that is no longer the case. Today, nearly 40,000 children and adults in the United States—and more than 100,000 worldwide—are living with cystic fibrosis.^[2]

Children born with cystic fibrosis between 2019 and 2023 are expected to live an average of 61 years. Even more encouragingly, on average, half of babies born in 2023 with cystic fibrosis are expected to reach the age of 68 or older. This represents a tremendous improvement compared to previous generations, when most people with cystic fibrosis died in childhood or their teenage years.^[2]

Most people with cystic fibrosis can now expect to live well into adulthood, with many living into their 40s, 50s, and beyond. Some patients are even living into their 70s. This increased survival is the result of multiple factors: widespread newborn screening programs that allow for early diagnosis, monitoring by specialized multidisciplinary care teams at cystic fibrosis centers, advances in treatments including new medications that target the underlying genetic defect, better infection control strategies, improved nutritional support, and the availability of lung transplantation for end-stage disease.^[2]

It’s important to note that survival can vary significantly based on individual circumstances. Factors that influence survival include the specific CFTR gene mutations a person has, how early the diagnosis was made, access to specialized care, adherence to treatment plans, and the development of complications. People who maintain good lung function, avoid serious infections, and manage their nutritional status tend to have better outcomes.^[6]

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