Cystic Fibrosis - Exams and Tests
Most people who
have cystic fibrosis have signs of it when they are children. Tests to diagnose
cystic fibrosis can be done at any time—before
pregnancy, during pregnancy, right after birth, in childhood, or in adulthood.
medical history and a
physical exam are often the first steps in diagnosing
cystic fibrosis, followed by screening or lab tests.
diagnosis of cystic fibrosis requires one of the
- Your child has early symptoms. These may include diarrhea that does not go away; large, greasy or very
smelly stools; constipation; not wanting to eat; or losing weight. To learn more, see Symptoms.
- A brother or sister who has cystic
- A positive
newborn screening test.
Also, there must be at least one of the following:
- Two positive
sweat tests on different dates. Sweat tests measure
the level of salt in sweat. People with cystic fibrosis have more than the
normal amount of salt in their sweat.
- A positive
genetic test for the genetic defect that is known to
cause cystic fibrosis. This testing can be done using blood or a sample from
the mother's womb before birth (chorionic villus sampling or
- An abnormal
nasal potential difference test. This test uses
electrodes on the lining of the nose to see how well salts flow into and out of
Monitoring cystic fibrosis
Certain tests can help your doctor monitor your child's cystic fibrosis.
These tests include:
- Lung function tests to find out how
healthy the lungs are by checking how well air moves into and out of the
throat culture or
sputum culture to see what kinds of bacteria are
causing any infections your child may have.
chest X-ray to take a picture of the chest, including
the heart and lungs.
CT scan to find any serious disease in the lungs,
pancreas, or other organs.
- Blood tests, such as glucose (blood
sugar) level and liver function. These tests are to see if there are any
complications of cystic fibrosis.
stool analysis to see how well your child is absorbing
and digesting fat and other nutrients.
arterial blood gas analysis to measure the levels of
oxygen and carbon dioxide in the blood. This test shows how well the lungs are
Both newborns and adults can be tested for the
changed (mutated) gene that causes cystic fibrosis. These tests include:
- Newborn screening. Levels of
a type of digestive enzyme are measured from a blood
sample. High levels of this enzyme suggest cystic fibrosis. Some newborns may also have
- Genetic test for adults. These tests identify the most common defects in the
cystic fibrosis transmembrane regulator (CFTR) gene. Genetic testing can be
done during pregnancy through chorionic villus sampling or amniocentesis. The
test can also be done before pregnancy, to help couples find out if
either or both of them carry a defective CFTR gene.
- If both parents
carry the changed gene, there is a 25% (1-in-4) chance that their child will
have no genetic problem. There is a 25% chance that their child will have cystic
fibrosis. And there is a 50% (1-in-2) chance that their child will be a
- If only one
parent is a carrier of the changed gene, the child will not have cystic
fibrosis. But there is a 50% chance that the child will be a carrier.
If you are interested in a genetic test for cystic
fibrosis, talk with your doctor about the test. Genetic counseling can help you understand your
test results. Genetic testing may involve certain ethical, legal, and religious issues.