Cystic Fibrosis (cont.)
Exams and Tests
Tests to diagnose cystic fibrosis can be done at any time—before pregnancy, during pregnancy, in childhood, or in adulthood. Genetic tests for couples who are planning a pregnancy or who are expecting a baby can help determine whether either person is a carrier of the changed (mutated) gene that causes cystic fibrosis. Babies can be screened for cystic fibrosis shortly after they are born, especially if they have symptoms or are at risk of inheriting the changed gene. Most people who have cystic fibrosis have signs of it when they are children.
A medical history and a physical exam are often the first steps in diagnosing cystic fibrosis, followed by screening or lab tests.
The diagnosis of cystic fibrosis requires one of the following:
- Your child has one or more of the common symptoms, including:
- A blockage of the small intestine at birth, called a meconium plug or meconium ileus.
- Salty sweat or skin.
- Not wanting to eat, having little energy, or losing weight. This is sometimes called failure to thrive.
- Inflammation of the pancreas (pancreatitis).
- Unusual bowel movements. This may include diarrhea that does not go away; large, greasy stools; very smelly stools; or constipation. If the intestines become blocked, the child's belly may stick out; and the child may not be able to have a bowel movement.
- Breathing problems, getting tired easily during activity, or repeated infections such as bronchitis or sinusitis.
- Wheezing and a cough that does not go away.
- A brother or sister who has cystic fibrosis.
- A positive newborn screening test. For this test, a small amount of the baby's blood is tested to see how much of a digestive enzyme called immunoreactive trypsinogen (IRT) is present. Babies with cystic fibrosis have more IRT than normal.
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. Genetic testing can be done using blood or a sample from the mother's womb before birth (chorionic villus sampling or amniocentesis).
- 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 cells.
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 lungs.
- A throat culture or sputum culture to see what kinds of bacteria are causing any infections your child may have.
- A chest X-ray to take a picture of the chest including the heart and lungs.
- A CT scan to identify any serious disease in the lungs, pancreas, or other organs.
- Blood tests, such as glucose (blood sugar) level and liver function, to see if there are any complications of cystic fibrosis.
- A stool analysis to see how well your child is absorbing and digesting fat and other nutrients.
- An arterial blood gas analysis to measure the levels of oxygen and carbon dioxide in the blood to see how well the lungs are working.
Both newborns and adults can be tested for the changed (mutated) gene that causes cystic fibrosis. These tests include:
- Newborn screening. Levels of immunoreactive trypsinogen (IRT), a digestive enzyme, are measured from a blood sample. High levels of IRT suggest cystic fibrosis. Some newborns may also have a genetic test for cystic fibrosis.
- 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 determine whether 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, a 25% chance that their child will have cystic fibrosis, and a 50% (1-in-2) chance that their child will be a carrier.
- 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 to understand your test results.