Testing for Cystic Fibrosis

If you, your child or another family member has just been diagnosed with cystic fibrosis (CF), or your doctor has recommended testing for CF, you may have many questions. How can you know for sure if you or your child has CF? If someone in your family has the disease, but you do not, could you pass it down to your children?

There are several ways to help answer these and other important questions.

Sweat Test

If a person shows symptoms of CF or if a baby has a positive newborn screen for CF, a doctor may order a sweat test. This simple, painless test is the best way to diagnose CF. It measures the concentration of salt in a person’s sweat. A high salt level indicates CF.

Sweat tests should be done at a Cystic Fibrosis Foundation-accredited care center, where strict guidelines help ensure accurate results.

Learn more about the sweat test.

Newborn Screening

Newborn screening for CF is done in the first 2 or 3 days after birth. It identifies babies who are at high risk of having CF. If a baby has a positive screen for CF, a sweat test may be used to rule out or confirm a CF diagnosis. All 50 states and the District of Columbia screen newborns for cystic fibrosis.

Newborns screened for CF can benefit from early diagnosis and treatment. Helping babies with CF get off to the best start can:

  • Improve growth
  • Help keep lungs healthy
  • Reduce hospital stays
  • Add years to life

Learn more about newborn screening.

Carrier Testing for CF

More than 10 million Americans are symptomless carriers of the defective CF gene. A genetic test for CF can help identify carriers who could pass CF onto their children. The test looks at a person’s genetic material using a blood sample or cells that are gently scraped from the inside of the cheek. Genetic testing is also often used to confirm a diagnosis of CF.

To have cystic fibrosis, a child must inherit one copy of the defective CF gene from each parent. Each time two carriers of the CF gene have a child, the chances are:

  • 25 percent (1 in 4) the child will have CF
  • 50 percent (1 in 2) the child will be a carrier but will not have CF
  • 25 percent (1 in 4) the child will not be a carrier of the gene and will not have CF

Learn more about genetic carrier testing.

For more information:

Updated: 5/1/2014