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Diagnosis of Cystic Fibrosis

How is cystic fibrosis diagnosed?

Newborns are screened for cystic fibrosis (CF) as part of each state's newborn screening program. If the results are positive, it does not mean your baby has cystic fibrosis. More tests are done as described below.

In addition to a full health history and physical exam, other tests for CF may include:

  • Sweat (chloride) test. This test measures the amount of chloride in the sweat. It's done by placing a solution on the forearm (or the thigh, if your child is too small) and attaching electrodes. The skin is stimulated to sweat with a mild electric current. This does not cause pain or harm your child. The sweat is collected onto a gauze pad and checked. Higher than normal amounts of chloride may suggest CF. The sweat test is not painful. It often causes only minor discomfort.

  • Genetic tests. Blood, or cells taken from a cheek scraping, can be tested for mutations in the CFTR gene. 

Your child may also have these tests:

  • Blood tests. These may include pancreatic function tests or tests to look for signs of infection. 

  • Chest X-rays or CT scans. These tests use invisible energy beams to make images of internal tissues, bones, and organs onto film.

  • Pulmonary function tests. These tests help measure the lungs' ability to exchange oxygen and carbon dioxide correctly. They are often done with special machines that a child must breathe into.

  • Sputum cultures. This test is done on the material that is coughed up from the lungs and into the mouth. A sputum culture is often done to find out if an infection is present.

  • Stool evaluations. These are done to measure the amount of fat in a stool sample. Too much fat may mean the digestive system is not working correctly.

Online Medical Reviewer: Daphne Pierce-Smith RN MSN
Online Medical Reviewer: David A Kaufman MD
Online Medical Reviewer: Raymond Turley Jr PA-C
Date Last Reviewed: 5/1/2021
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