Cystic fibrosis

Cystic fibrosis is a genetic disease that mainly affects the respiratory and digestive systems. It causes secretions to thicken, which interferes with the proper function of the lungs and pancreas. The disease can be mild to severe and can affect people in different ways.

An estimated 1 in 2,500 children in Quebec is born with cystic fibrosis.


Cystic fibrosis symptoms and their severity can vary from person to person.

The main symptoms are:

  • persistent cough with thick secretions;
  • wheezing and shortness of breath, including severe breathing problems;
  • poor absorption of food that can lead to:
  • little weight gain
  • weightloss,
  • stunted growth,
  • vitamin deficiencies;
  • Recurring respiratory tract infections, such as pneumonia, which can get worse from one moment to the next;
  • intestinal disorders such as intestinal obstruction and frequent greasy stools; fertility problems.


Cystic fibrosis is a recessive inherited disease that is passed to a child by two parents who carry the same defective gene. The affected person is born with the disease. For more information, go to the Transmission of Hereditary Recessive Diseases page.

Diagnosis by sweat test

Under the Quebec Neonatal Blood and Urine Screening Program, a blood sample is taken from your baby’s heel to screen for a number of diseases, including cystic fibrosis. If the result is abnormal for the disease, an additional test should be done. It’s called a sweat test and it will determine if your child has cystic fibrosis and if follow-up is needed.

A sweat test involves collecting a small amount of your child’s sweat to measure the salt concentration. People with cystic fibrosis have a higher concentration of salt in their sweat.

Test procedure

A sweat test is performed at a referral center. It is painless and takes between 30 and 40 minutes.

The boy’s sweat is collected from her arm. The steps are the following:

  1. A device that stimulates sweating is attached to the child’s arm and held in place for a few minutes.
  2. The device is removed and a piece of filter paper is taped to the stimulated area.
  3. A plastic film is placed over the area to keep the arm warm and allow sweat to collect on the filter paper for about 30 minutes. You can hold your child to comfort and reassure him, and you can even breastfeed or give him a bottle.
  4. The filter paper is removed and it takes staff 5-10 minutes to check if enough sweat has collected. The arm may be a little red, but this is normal and does not hurt.
  5. The filter paper is sent to the laboratory for analysis.

The test result will be available in a few hours. A member of the cystic fibrosis team at the referral center will come and explain the result and answer all of her questions.

Test results

In most cases, the sweat test confirms that the child does not have cystic fibrosis.

If the test confirms that your child has cystic fibrosis, he or she will get the care that he needs.

If your child is a carrier, she will not need any particular follow-up. A healthy carrier is not sick and is not at risk of developing the disease.

Carrier status

In Quebec, around 1 in 20 people is a carrier of cystic fibrosis. A carrier has a defective gene associated with cystic fibrosis. They are not sick and are not at risk of developing the disease. For more information on how genes are passed on, go to the Transmission of Hereditary Recessive Diseases page.

There is a chance that the sweat test is normal, but the child actually has the disease. However, it is very low. A sweat test can identify about 90% of all faulty genes associated with cystic fibrosis, that is, the most common. Although highly unlikely, your child could have a second faulty gene that was not identified during the test. These less common faulty genes that are not identified during the test often cause milder forms of the disease that appear later.

If you are concerned about your child’s health or have frequent respiratory or digestive problems or growth retardation, talk to your doctor. They can request another evaluation if necessary.

If your child’s sweat test shows that he is a carrier of the disease, she may want to find out her carrier status or that of other family members.

Parent carrier status

If the sweat test confirms that your child carries a defective gene for cystic fibrosis, one of the parents must necessarily carry the gene. The second parent could be a carrier of a defective fibrosis gene

Carrier status of other children in the family

Your other children might also be healthy carriers. If they are healthy, additional tests will not be necessary. Later, when they are old enough to be parents and if they want to, they can be seen in medical genetics to find out if they carry the defective gene.

By Mashid

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