What is a Newborn Screening for Cystic Fibrosis?

My Baby had a Positive Newborn Screen for CF:

It is important to know that most babies who screen positive for cystic fibrosis (CF) do not have it.

Before you took your newborn baby home from the hospital, a small amount of blood was taken from his or her foot as part of Ohio’s Newborn Screening Program. One of your baby’s test results showed a need for a second test called a sweat test.

If you had a negative CF blood test when you were pregnant, but your baby’s newborn screening was positive for CF, your baby should still have a sweat test. The CF carrier testing available to parents during pregnancy cannot rule out the possibility that their baby could have CF.

Why does my baby need a sweat test?

This test is the best way of checking for cystic fibrosis (CF). Babies with CF typically have saltier sweat than normal. The sweat test will measure how much salt is in your baby’s sweat.

Most babies (about 90%) who get a sweat test do not have CF, but it is important to make sure. However, if CF is diagnosed, we know that early treatment by CF specialists is very beneficial.

The sweat test: what to expect

The sweat test takes about one hour from start to finish.

A special machine causes a small part of the baby’s arm or leg to sweat. The skin may feel warm and tingly for five minutes while the machine is on. Your baby may cry during this part of the test, but it is not painful. Sometimes, this process can cause skin irritation on the baby’s skin, but not usually. The sweat is collected on a special coil. After 30 minutes, the coil is removed, and the sweat is tested in the lab.

Do not use any lotions or creams on your baby’s arms or legs for the 24 hours before the test (including moisturizing soaps). Be sure to dress your baby in warm clothing and allow him/her to have plenty to drink. No other special preparations are needed prior to your appointment.

You will meet with a genetic counselor on the day of the sweat test. The genetic counselor talks to you about how CF is inherited. They also talk about the possible results from the sweat test and what they mean.

What do the results mean?

The genetic counselor calls you with the test results. These results are also shared with your child’s primary care provider. Results differ by state, but there are four possible results for Ohio:

Negative Result: This means that a normal amount of salt was found in the sweat. It is very rare for a person to have CF if the sweat test result is negative. Your baby should get regular medical care, but no additional follow up is needed. However, this result means your baby is most likely a CF carrier.

Positive Result: A positive sweat test means that your baby probably has CF. A second sweat test should be done to confirm a CF diagnosis. Your primary care doctor will help you get an appointment with a doctor and team of clinicians who specialize in treating CF.

Borderline Results: Sometimes the sweat test result will be in between positive and negative. Your baby will need another sweat test, and perhaps an exam and blood test.

“QNS” (Quantity Not Sufficient): QNS means there was not enough sweat collected. You will be asked to bring your baby back for further testing when he/she is bigger, usually in about two weeks.

What does it mean to be a CF carrier?

CF carriers are healthy, and their sweat test results usually are normal. A CF carrier has one gene for CF, but doesn’t have the two genes required to cause CF. If your baby is a CF carrier, then one of the parents must also be a CF carrier. And there is the possibility that both parents are CF carriers. This means that they could have a child with CF in the future.

The genetic counselor meets with you while your baby’s sweat test is done. The counselor answers questions about being a CF carrier and gives you written information.

Additional Resources

To learn more about CF newborn screening, sweat testing, and CF carriers visit the CF Foundation website at these links:

• Newborn Screening for CF
• Carrier Testing for Cystic Fibrosis

Should I be worried?

Remember, most babies who get a sweat test do not have CF, but this can still be a stressful time.

Please reach out to your primary care provider, or our CF team, with any questions that aren’t fully answered here. Some parents may need help with the stress of a possible CF diagnosis, and have found the following resources helpful:

• 5 Things You Should Know About Stress
• Stress Management