Cystic Fibrosis (CF) Newborn Screening: Sweat Testing
If a newborn screen test shows your baby might have cystic fibrosis (CF), a sweat test will make the final determination. The sweat test should be done in a Cystic Fibrosis Foundation accredited center to make sure that the test results are accurate.
What happens during a sweat test?
The sweat test measures the amount of salt in the sweat. No needles are used and the test will not hurt your baby. In the first part of the test, a special chemical with no color and no odor that is known to cause sweating will be put on a small area on both of your baby's arms. A weak electrical current is then passed through the skin by attaching small electrodes to the arm with an armband. This causes a tingling feeling much like when your arm is "asleep." Paper pads are used to collect the sweat. The sweat will then be taken to a lab, where the rest of the test will be completed.
What will the sweat test tell me?
Children and adults with cystic fibrosis have an increased amount of sodium and chloride (salt) in their sweat. In infants, sweat test results can be normal (meaning your baby does not have cystic fibrosis), borderline (meaning the results of the test may be uncertain), or positive (meaning that your baby has cystic fibrosis). For individuals who have cystic fibrosis, the sweat test will be positive from birth. Once a test result is positive, it is always positive. Sweat test results do not change when a baby has a cold or other illness.
Preparing for the Sweat Test
Parents should not apply creams or lotions to the baby's skin 24 hours prior to the sweat test. There are no other special preparations before the test. There is no need to change the baby’s diet or other activity. All regular medications may be used and will have no effect on the test results. Feeding your baby just prior to or during the test may help your baby to sweat. It also helps to have warm clothes or blankets to wrap your baby in during the test.
Sweat Test Results
The lab will usually have the sweat test results ready for your doctor a few hours after the sweat is collected. The clinic where the sweat test is done will tell you how they will inform you of the test results.
In a small number of cases, the test results fall into the "borderline" range between not having cystic fibrosis and having cystic fibrosis. When this occurs, repeat sweat tests or blood tests may be done. These will only be done after talking to a doctor.
What is a false-positive?
When a child has an abnormal screening test followed by a normal sweat test, the screening test is referred to as a false-positive result. Children with false-positive screening tests do not have cystic fibrosis.