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Tests and diagnosis
By Mayo Clinic staffIf you're pregnant or trying to become pregnant, you may want to consider talking to your doctor about a cystic fibrosis carrier test for you and your partner. In the past, doctors usually tested only couples at increased risk — those with a personal or family history of cystic fibrosis — but many doctors now offer the test to all couples.
The test, which is performed in a lab on a sample of blood or saliva, can help determine whether you or your partner carries the gene for cystic fibrosis. If you're already pregnant and the test shows that your baby may be at risk of cystic fibrosis, your doctor can conduct additional tests on your developing child. Because cystic fibrosis can't be treated before birth, the purpose of these tests is to help you consider your plans for the future.
The decision to be screened for cystic fibrosis is personal and will depend on a number of factors, including your level of risk and your religious beliefs. In addition, some genetic mutations for cystic fibrosis can't be detected by the current test. That means that in rare cases, your test may be normal and yet you may still be a carrier. The chances of this happening are small, however.
Sweat test
The standard diagnostic test for cystic fibrosis is a sweat test, which measures the amount of sodium or chloride in a person's sweat. During the procedure, a small amount of an odorless sweat-producing chemical is applied to a small area on the arm or leg. An electrode attached to the area stimulates a very weak and painless electric current, causing a tingling or warm feeling. After several minutes, sweat is collected from the stimulated area and sent to a laboratory for analysis.
The sweat test is performed on two separate samples, which are usually taken on one occasion, to ensure that a false-positive or false-negative result hasn't occurred. A consistently high level of salt indicates cystic fibrosis. This test doesn't show whether someone has a mild or severe case of the disease, however, and it can't predict how well someone with cystic fibrosis will do.
In addition, the sweat test may not always be useful in newborns. That's because babies may not produce enough sweat for a reliable diagnosis in the first month of life. For this reason, doctors usually don't perform a sweat test until an infant is at least several months old.
Other tests
If your newborn has signs and symptoms of cystic fibrosis, your doctor may perform a genetic analysis of a blood sample to confirm the diagnosis. Tests may also help determine the extent and severity of cystic fibrosis. Among these are tests to measure how well the lungs, pancreas and liver are working.
Because cystic fibrosis is an inherited disease, your doctor may suggest testing the brothers and sisters of a child with cystic fibrosis, even if they show no signs or symptoms. Other family members, especially first cousins, also may want to be tested. In most cases family members can be screened with a sweat test, although in some cases genetic blood testing may be appropriate.
