Screening Newborns for Cystic Fibrosis

Newborns with CF can benefit from early diagnosis and treatment. In fact, specialized care and new cystic fibrosis therapies have improved the length and quality of life for people with this disease.

What is a Cystic Fibrosis Carrier?

CF is a genetic disease caused by a recessive gene. This means a child must inherit two copies of the CF gene—one from each parent—to have the disease.

A CF carrier is a person with one working copy of the CF gene. The other copy is abnormal. A carrier is perfectly healthy and does not have CF.

When both parents are carriers, for each pregnancy:

  • They have a 25 percent chance of having a child with CF.
  • They have a 50 percent chance of having a child who is a CF carrier.
  • They have a 25 percent chance of having a child who does not have CF and is not a carrier.

These percentages are the same for every pregnancy, even if the couple has already had a child with CF.

The test used to screen newborns for CF measures how much immunoreactive trypsinogen (IRT) is in the baby’s blood. IRT is a digestive enzyme made by the pancreas. Infants who have CF may have increased levels of IRT in their blood for several months after birth.

Before you take your newborn home from the hospital, a small amount of blood will be taken from his foot as part of the Georgia Newborn Screening Program. If the test results show a high level of IRT, the blood will then be tested for the presence of any CF mutations. If even one is found, then your baby will need to have a second test called a sweat test to rule out or confirm a diagnosis.

It is important to know that only about one in 10 babies with a positive newborn screening test for CF have the disease. The others are just carriers of the gene and will be healthy, normal infants. In order to confirm or rule out the disease, a sweat test must be performed.

Sweat Test

The sweat test is the best way to diagnose CF. The sweat test will measure how much salt is in your baby’s sweat. The CF gene affects how salt and water move through the body’s cells.

No needles are used and the sweat test will not hurt your baby.

Here is what happens during a sweat test:

  • A special chemical with no color and no smell will be put on a small area on both of your baby’s arms. The chemical will cause your baby to sweat in the area to which it is applied.
  • A weak electrical current from a battery 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 be taken to a lab. The lab will usually have the sweat test results ready for your doctor a few hours after the sweat is collected.

There are four possible results:

  • 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.
  • Positive result—A positive sweat test means your baby has CF.
  • Borderline result—This means the results of the test were uncertain. You will be asked to bring your baby back for another sweat test, and maybe an exam and blood test.
  • Quantity not sufficient (QNS)—This means there was not enough sweat collected during the test. You will be asked to bring the baby back another day to try again.

A positive result is one in which the saltiness of your baby’s sweat is more than three times higher than normal.

Sweat test results do not change when a baby has a cold or other illness.