Cystic Fibrosis Diagnostic Testing

Is Testing Right for Me? I Have My Test Results

Cystic Fibrosis Diagnostic Testing

What Is Cystic Fibrosis?

Cystic fibrosis (CF) is an inherited condition that causes a range of symptoms including breathing (respiratory) difficulties, digestive problems, and infertility in men.

CF causes certain organs in the body to make thick, sticky mucous. In the lungs, this mucous can cause breathing difficulties, chronic lung infections, and progressive loss of lung function. In the pancreas, the mucous interferes with the pancreatic enzymes that help break down and digest food. As a result, people with CF may have problems with growth, weight gain, and the absorption of nutrients — sometimes called "failure to thrive" in children.

Many factors affect how severe CF is, including the specific mutations that are causing CF, other genes, and environmental factors. Most often, CF develops in childhood and leads to long-term complications. The symptoms usually get worse with age and lead to a shortened life span. The average life span of a person with classic CF is the mid-30s, although that is gradually getting better with medical advances in treatment.

Occasionally, CF can have much more mild symptoms and may not be diagnosed until adulthood.

Early diagnosis and effective treatment are essential to improve quality of life and life span. Treatments are available to slow progression of the disease, reduce or relieve symptoms, and prolong lifespan. There is currently no cure for CF.

Cystic fibrosis doesn't cause changes in intelligence or appearance.

CF affects at least 30,000 children and adults in the United States. More than 10 million people in this country are unaffected carriers, meaning that they have one copy of a CF gene mutation. CF carriers are discussed further in Genetics of Cystic Fibrosis.

Next: What is Newborn Screening?

Why are you considering genetic testing for yourself or your child?

I think I might have CF, but I haven't seen a doctor yet.

I have a definite diagnosis of CF based on sweat chloride testing, but I have not yet had genetic testing.

I might have CF, but my sweat chloride test results were uncertain (intermediate).

My baby had a positive newborn screen result.

None of these.

The symptoms you may feel from CF can be similar to symptoms caused by many different conditions. People with symptoms of breathing or nutrition problems may need lab tests, imaging, breathing tests, and other tests to help a doctor find the likely cause of those symptoms.

Diagnostic testing may be considered if other, common causes have been ruled out. CF is usually diagnosed with a test called a sweat chloride testing. This test measures the amount of salt in your sweat. A positive sweat chloride test can diagnose CF for sure. Genetic testing may be used in addition to sweat chloride testing.

Although you already know you have CF, genetic testing may be useful for you. Genetic testing can:

  • Confirm your diagnosis
  • Provide some information about how CF may affect you
  • Define your gene changes (mutations) so that accurate testing is available for your family members

When testing finds two mutations, the results confirm that you have CF. If family members decide to have CF testing, they should be checked for the mutations found in you.

When testing finds one or no mutations, it doesn't mean that you don't have CF. If you've had a positive sweat chloride test, then that testing confirms your diagnosis. Genetic testing can't find all of the gene mutations that cause CF. Depending on which type of genetic testing you have, additional testing may be available to help find your mutations.

There are several different ways (methods) of genetic testing. You should talk to your doctor about which test method may be best for you. Some type of expanded testing may be needed for you, especially if you aren't Caucasian or Ashkenazi Jewish.

Genetic testing may be useful to clarify whether or not you have CF.

When testing finds two mutations, the results confirm that you have CF. Having this information may provide you and your doctor some information about how you'll be affected by CF. Family members can have testing that looks for the mutations found in you.

When testing finds one or no mutations, it doesn't rule out CF. Genetic testing can't find all of the gene mutations that cause CF. Repeat sweat chloride testing and possibly some other kinds of tests may be helpful to figure out whether you have CF or not.

There are several different ways that testing can be done for CF. For people who have symptoms of CF but an intermediate sweat chloride result, medical guidelines recommend some type of more detailed testing. Testing by an expanded panel or gene sequencing will increase the chance that testing will find the mutations if they are there.

Genetic testing may be useful to clarify whether or not your child has CF. However, the decision to test will depend on what kinds of tests have already been done.

Newborn screening varies from state to state. Some states check for CF in newborns by testing for a protein called immunoreactive trypsinogen (IRT) only. Other states use IRT plus genetic testing. The way genetic testing is done (testing method) also depends on the state.

All newborns that have tested positive by newborn screening should have a sweat chloride testing. If your child has not yet had that testing, you should talk to your pediatrician about having it done as soon as possible. This test measures the amount of salt in sweat. A positive sweat chloride test can diagnose CF for sure. Genetic testing may be used in addition to sweat chloride testing.

When genetic testing finds two mutations, the results confirm that your child has CF. Having this information may provide you and your child's doctor some information about how he or she will be affected by CF. Testing may also be useful for other family members, including you, your partner, and any of your other children.

When genetic testing finds one mutation, it doesn't rule out CF. Genetic testing can't find all of the gene mutations that cause CF. Sweat chloride testing and possibly some other kinds of tests may be helpful to figure out whether your child has CF or not. If sweat chloride testing is negative, then your child is a carrier. Carriers don't usually have any health problems related to CF.

When genetic testing finds no mutations, it doesn't rule out CF. Genetic testing can't find all of the gene mutations that cause CF. Sweat chloride testing and possibly some other kinds of tests may be helpful to figure out whether your child has CF or not. If sweat chloride testing is negative, then your child doesn't have CF. This can happen when there is a false positive newborn screen.

You should talk to your child's doctor about exactly what kind of testing has already been done for your child as part of newborn screening.

CF genetic testing to make a diagnosis probably won't be useful for you if you don't have signs of CF. However, there are other reasons for CF genetic testing, including carrier testing for couples planning a pregnancy or currently pregnant. Men with congenital absence of the vas deferens (CAVD) and their partners may also consider CF testing.

If you think you have another reason to consider CF testing that isn't discussed here, talk to your doctor or a genetic counselor.