Cystic Fibrosis (CF) Diagnosis | National Jewish Health

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

Diagnosing Children with Cystic Fibrosis

Children are most often diagnosed with cystic fibrosis through newborn screening tests.

Newborn Screening

Newborn screening for cystic fibrosis is now required in all 50 states and the District of Columbia. Many studies have proven that CF diagnosed early in life results in healthier children and increased survival rates when compared to children with a delayed diagnosis. The United States Centers for Disease Control and Prevention (CDC) and the Cystic Fibrosis Foundation recommend newborn screening. The test detects elevated quantities of trypsinogen in a drop of blood collected from the heel. This procedure (blood collected from the heel) is already widely performed to test for other congenital disorders. Newborn screening is not a definitive diagnostic test for cystic fibrosis. If the test is positive, a sweat test and genetic testing may be done.

Diagnosing Adults with Cystic Fibrosis

Most adult diagnoses are made after symptoms are present. The most common symptoms of CF in adult patients include:

Chronic coughing
Recurrent sinus and lung infections
Bronchiectasis
Pancreatitis
Infertility
Inability to gain weight
Abnormal bowel movements

Mild forms of CF can remain undiagnosed until adulthood. Most people with cystic fibrosis diagnosed in adulthood will have normal pancreatic function.

The life expectancy of people diagnosed as adults with nonclassic CF is significantly longer than for people diagnosed in childhood. The people diagnosed later in life also respond well to standard CF care.

Testing for Cystic Fibrosis

Reliable testing is one of the most significant advances in our understanding and treatment of CF. Testing is important for children and adults suspected of having the disease. It is also important for individuals without symptoms who are concerned about the risk of being a CF carrier and passing the CF gene to their children.

Sweat Test

This test is the gold standard for diagnosing CF. Sweat tests must be performed by trained technicians and evaluated in a Cystic Fibrosis Foundation-accredited Care Center where strict guidelines help ensure accurate results. National Jewish Health is an approved diagnostic laboratory for cystic fibrosis.

The sweat test is performed on children and adults who show symptoms of cystic fibrosis or babies who have a positive newborn screen for CF.

It is a painless test that looks a high chloride level.

Less than or equal to 29 mmol/L = CF is unlikely regardless of age.
Between 30-59 mmol/L = CF is possible, and additional testing is needed.
Greater than or equal to 60 mmol/L = CF is likely to be diagnosed.

If sweat test results are between 30-59 mmol/L, the sweat test is usually repeated.

Genetic Testing

Genetic testing for CF analyzes a person’s DNA (genetic material) from a blood sample or from cells that are gently scraped from inside the mouth. Genetic testing looks for the most common CFTR mutations, which account for up to 90 percent of all cases in specific ethnic groups. There are more than 1,700 known CFTR mutations.

Several tests can identify the presence of defective CFTR genes in newborns with positive screening results, as well as children and adults with symptoms of CF. These tests can also identify symptomless carriers of an abnormal CF gene.

The American College of Obstetricians and Gynecologists recommends that all pregnant women and their partners, as well as couples planning to have children, have genetic testing to screen for carriers of CF.

Patients confirmed to have CF by the sweat test can benefit from genetic testing. It can identify the specific CFTR mutations and help predict the future severity of the condition. Newer treatments are also focused on specific CFTR mutations.

Cystic Fibrosis: Diagnosis