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Cystic fibrosis (CF)

Cystic fibrosis (CF) is an inherited condition. It is caused by a problem with the CF gene.

CF causes some organs in the body such as the lungs and pancreas to produce thick mucus.

The mucus can build up in the lungs and cause chest infections. These infections can cause lung damage over time.

CF can cause other problems. For example, the mucus produced by the pancreas can stop digestive enzymes getting to the intestine. People with CF can find it hard to digest food or gain weight.

Babies born in Ireland with CF

Around 1 in 2,300 babies born in Ireland has CF.

About 1 in every 19 people has 1 copy of the altered CF gene and 1 copy of the unaltered gene. These people do not have CF.

If both parents carry the altered gene, they have a 1 in 4 chance of having a baby with CF.

How heel prick screening can help

If the heel prick suggests your baby may have CF, they will be referred to a specialist.

Your baby can then start treatment with a high-energy diet to help them gain weight. Your baby can also get medicine and physiotherapy to improve their lung function.

A child with CF may still become ill. Early treatment improves their quality of life and can reduce the time they need to spend in hospital.


The heel prick will not detect all babies with CF, especially if they have a rare copy of the altered CF gene.

If you think your baby may have signs of CF, speak to your GP.

If your baby's heel prick result shows that they may have CF

Your baby will see a doctor who specialises in children who have CF.

They will do a sweat test. This will show us if they carry 1 copy of the altered CF gene, or if they actually have CF.

As your baby does not need urgent treatment or special care, you should continue to care for your baby as you have been.

The sweat test

The sweat test is the best way to diagnose CF.
People with CF have a large amount of salt in their sweat. Measuring the amount of salt in their sweat will confirm if your baby has CF. The test does not hurt your baby.

Do not apply creams or lotions to your baby’s skin 24 hours before the test.

How the sweat test works

In the first part of the test, we put a medicine that causes sweating on a small area on your baby’s arm or leg. Then we put an electrode over that spot. A weak electrical current is applied to the area to cause sweating.

Your baby may feel a slight tingling in the area, or a feeling of warmth. This part of the test lasts about 5 minutes.

In the second part of the test we collect the sweat on a piece of filter paper, gauze or a plastic coil. This takes about 30 minutes. We send the sweat to a laboratory to measure how much chloride is in the sweat.

You will get the results a few hours later.

If your baby carries the CF gene

If your baby carries one copy of the altered CF gene they will not have CF and will not need any special treatment.

1 in 19 people in Ireland are healthy carriers of the CF gene. You may wish to tell your child later in life that they carry an altered CF gene.

All parents of babies who are identified as having 1 altered CF gene are referred for genetic counselling and genetic testing if required.

Because there is a possibility your child has a second altered gene that we have not identified, we will perform a sweat test.

Page last reviewed: 3 January 2023
Next review due: 3 January 2026