Skip to main content

Cystic Fibrosis

Cystic fibrosis (CF) is an inherited life-limiting disorder. It causes thick mucus to build up in the lungs, digestive system (and pancreas) and other organs. Most people with CF get chest infections. They also have problems digesting their food and, as a result, they may not gain weight as well as they should. Screening means that babies with CF can receive early treatment with medicines and physical therapy that help them digest food and keep their lungs clear of mucus. This treatment will help prevent serious illness and allow the child to live a healthier life. About one baby in 3,600 in BC is born with CF. 

For more information:

Screening

The process used to screen for cystic fibrosis is described below:

1Measure Protein in Blood

Using the blood spots from a baby’s heel prick, the level of a protein in your baby’s blood is measured. The protein is called immunoreactive trypsinogen (IRT).

  • If the IRT level is normal, this is considered a negative screen for CF. No further testing is required.
  • If the IRT level is higher than normal, the lab will do another test on the same blood sample. This test is called a DNA test (see step 2).

2DNA Test

The DNA test looks for common changes in the CF gene. What is the CF gene? People’s bodies are made up of tiny building blocks called cells. Inside the cells are tens of thousands of instructions called genes. Genes tell the body how to grow and develop. Two copies of each gene are present, one copy from the mother and one from the father. The DNA test looks for changes (called mutations) that happen in one of the baby’s genes (the CF gene).

  • Babies with a change (mutation) in both copies of the CF gene are likely to have CF.
  • Babies with a change (mutation) in one copy of the CF gene may have CF or may be healthy “carriers” for CF.

The next step depends on the results of the DNA test. 

3Sweat Test

If a baby has a change (mutation) in both copies of the CF gene, the baby is likely to have CF. A sweat test will be done to find out for sure.

If the baby has a change (mutation) in one copy of the CF gene, a repeat blood sample is taken when the baby is 21 days old. This sample is tested to see if your baby’s IRT level is still increased.

  • What if the second IRT is normal? If the baby's IRT level on the second blood sample taken at three weeks of age is normal, it is very unlikely that the baby has CF but instead is likely a healthy CF carrier. The baby may be have a sweat test to be sure if this is desired by the parents.
  • What if the second IRT is high? If the baby’s IRT level is still increased, the baby may have CF or may be a healthy CF carrier. A sweat test will be done to learn more.
  • Information Sheet: High IRT and One Mutation 
If a baby has no changes in either copy of the gene, a repeat blood sample is taken when the baby is 21 days old. This sample is tested to see if your baby’s IRT level is still increased. This second IRT level is a better indicator of CF than the one done at 24-48 hours of age.

  • What if the second IRT is normal? If the baby’s IRT level on the second blood sample taken at 3 weeks of age is normal, the baby is very unlikely to have CF. No more testing will be done.
  • What if the second IRT is high? If the baby’s IRT level is still increased, this may mean that the baby has CF. A sweat test will be done to learn more.
  • Information Sheet: High IRT and No Mutations 
SOURCE: Cystic Fibrosis ( )
Page printed: . Unofficial document if printed. Please refer to SOURCE for latest information.

Copyright © Perinatal Services BC. All Rights Reserved.

    Copyright © 2017 Provincial Health Services Authority.