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Cystic Fibrosis: Newborn Screening and Diagnosis

Aug 24, 2023
physician screening newborn for cystic fibrosis

Within the first few days of a newborn baby’s life, a blood test is done. This newborn screening tests for many diseases that can be found and treated early in life, including cystic fibrosis (CF).

What Is Cystic Fibrosis?

Cystic fibrosis is a genetic disease that causes thick sticky mucus to form throughout the body. This most commonly causes problems with breathing and digestion, but CF can affect the whole body. There are many new medicines and treatments available today.

How Do You Screen for Cystic Fibrosis?

There are two steps to the newborn screening test for CF in Ohio.

  1. The blood is tested for a chemical called IRT (immunoreactive trypsinogen). Babies with CF usually have high IRT levels.
  2. If the IRT is high, genetic testing is done on the same sample. This looks for the most common genetic changes (mutations) that can cause CF.

A newborn screening test is flagged as abnormal if at least one genetic change (mutation) is found. The newborn screening does NOT test for all the possible genetic changes (mutations) that can cause CF. This is why more testing is needed to figure out whether a baby has cystic fibrosis or is a carrier.

Nine out of ten babies with an abnormal newborn screening for CF do NOT have cystic fibrosis, but instead are CF carriers.

Rarely, the newborn screening process can miss someone who has CF. If there is any concern your child has CF, more testing should be done even if the newborn screening was normal.

How Is Cystic Fibrosis Diagnosed?

A sweat chloride test is the best test to figure out if a baby has CF. Any baby with an abnormal newborn screening or symptoms concerning for CF should have a sweat test at a cystic fibrosis center.

The sweat chloride test measures how much salt is in the sweat. If the sweat test is high enough, it means the baby has CF. Babies with CF have salty sweat.

What Is the Difference Between Having Cystic Fibrosis and Being a Carrier?

Carriers have one genetic change (mutation) in the CF gene, but do not actually have CF or develop symptoms. Carriers can pass on the genetic change (mutation) in the CF gene if they have a baby.

People with CF have two genetic changes (mutations). This causes thick sticky mucus to develop in the body which causes symptoms and an abnormal sweat test.





Genetic testing finds 2 gene changes (mutations) that cause CF.

Genetic testing finds 1 gene change (mutation) that causes CF and 1 working copy of the gene.

Sweat Test

Sweat test is high (>59).

Sweat test is normal (<30).


Sticky mucus builds up in the body and causes symptoms in the lungs and digestive tract.

No symptoms because the 1 working gene makes up for the non-working gene.

How Is the Cystic Fibrosis Gene Passed Down?

  • Babies get one copy of this gene from each parent.
  • To have a child with cystic fibrosis, both parents must have at least one genetic change (mutation). This means both parents must either be carriers or have CF.
  • It can be helpful to get genetic testing for the parents of babies who either are carriers or have CF to help figure out the risk of having another baby who is a carrier or has CF.
  • More testing is needed for babies with an abnormal newborn screening for CF even if one or both parents have had normal CF carrier screening.

diagram explaining the genetics of cystic fibrosis

If you have any concerns that your baby might have CF, ask your child’s pediatrician for a referral to a CF center. Visit the Cystic Fibrosis Foundation website for more information and national resources.

Pediatric Cystic Fibrosis Program at Nationwide Children's Hospital
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Featured Expert

Brittney Haas
Brittney N. Haas, FNP
Pulmonary Medicine

Brittney N. Haas, FNP is a Nurse Practitioner on the Pulmonary Medicine team at Nationwide Children's Hospital.

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700 Children’s® features the most current pediatric health care information and research from our pediatric experts – physicians and specialists who have seen it all. Many of them are parents and bring a special understanding to what our patients and families experience. If you have a child – or care for a child – 700 Children’s was created especially for you.