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Cystic fibrosis

How is cystic fibrosis diagnosed?

In the UK, all newborn babies are tested for cystic fibrosis.

Blood spot test

The blood spot test is sometimes called the heel prick test. A small sample of blood is taken from your baby’s heel. You’ll be offered this when your baby is 5 days old. This blood is sent to a lab where it’s tested for a number of conditions, including cystic fibrosis.

If the blood spot test shows there may be a problem, your baby will need some more tests to confirm the diagnosis.

Sweat test

A sweat test involves taking a sample of your child’s sweat to test how much salt it contains. People with cystic fibrosis have more salt in their sweat. This is the best way to diagnose cystic fibrosis.

Genetic test

Your child might also have a genetic test. A doctor will take a blood sample. This will be tested for the genes that cause cystic fibrosis.

Testing family members

If your child is diagnosed with cystic fibrosis, any brothers or sisters they have will also need to be tested for the condition.

If a member of your family is diagnosed with cystic fibrosis, there’s a chance that you could be a carrier of the faulty gene. It’s a good idea to have a carrier test to find out if you are a carrier. Your doctor or nurse will take a genetic sample using a special mouthwash or take a blood sample to be tested.

Next: How is cystic fibrosis treated? >

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Last medically reviewed: September 2019. Due for review: September 2022

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.