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Cystic fibrosis

Read about the tests that may be carried out to diagnose cystic fibrosis, including newborn screening tests, the sweat test and genetic testing.

Tests can be carried out to diagnose cystic fibrosis at any age.

Most cases are now detected soon after birth through newborn screening, but older children and adults with symptoms of cystic fibrosis who weren't screened can also have tests to check for the condition.

Tests to find out if you are a "carrier" of the faulty gene responsible for cystic fibrosis may also be recommended for some people.

Newborn screening

newborn blood spot test is now offered to all babies in England to help detect problems early on, including cystic fibrosis.

When your baby is five to eight days old, a health professional will prick their heel and collect drops of blood on a special card. The blood is then sent to a laboratory to be checked for abnormalities that could indicate cystic fibrosis.

You should receive the results by the time your baby is six to eight weeks old. You will be contacted sooner if a problem is found, and you'll be asked to attend a hospital appointment.

The screening result isn't 100% accurate, so more tests will be carried out to confirm the diagnosis. You, your partner and any other children you have may also be tested to see if you carry the faulty gene that causes cystic fibrosis (see below).

Confirming a diagnosis

Tests to confirm a diagnosis will be carried out if screening suggests that your child may have cystic fibrosis, or your doctor thinks you could have the condition and you haven't been screened previously.

Two main tests can be used to diagnose cystic fibrosis:

  • sweat test – a test to measure the amount of salt in sweat, as the sweat of someone with cystic fibrosis has higher levels of salt than normal
  • genetic test – where a sample of blood or saliva is checked for the faulty gene that causes cystic fibrosis

The sweat test is most commonly used, although genetic testing may be done if the sweat test result is inconclusive or to identify the specific genetic fault that's causing the condition.

Carrier testing

Testing to find out if you carry the faulty gene that causes cystic fibrosis may be useful if:

  • you have a close relative, such as a child, sibling or parent, who's a known carrier
  • you have a close relative with cystic fibrosis
  • your partner is known to carry the cystic fibrosis gene

This can be done using a blood test, or occasionally a special mouthwash, to collect a sample of cells. The sample is then sent to a laboratory so it can be checked for the faulty gene.

Finding out whether you're a carrier of the faulty gene can help determine if you're at risk of having a child with cystic fibrosis. A genetic counsellor will explain the results of the test to you and discuss the implications and options available for future pregnancies.

Blood test
During a blood test, a sample of blood is taken from a vein using a needle, so it can be examined in a laboratory.
Chorionic villus sampling
Chorionic villus sampling is a test during pregnancy to see if there are any genetic problems with the foetus. A small sample of tissue is taken from the placenta.
Counselling is guided discussion with an independent, trained person to help you find your own answers to a problem or issue.
Genes contain information that you inherit from your parents, such as eye or hair colour. They are carried by chromosomes.
Genetic is a term that refers to genes, the characteristics inherited from a parent.
Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.
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