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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. Additional tests are done as described below.

In addition to a complete medical 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, which does not cause pain or harm to your child. The sweat is collected onto a gauze pad and analyzed. Higher than normal amounts of chloride may suggest CF. The sweat test is not painful and usually causes only minor discomfort.

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

As part of the assessment of CF symptoms, your child may also have these tests:

  • Blood tests. These may include pancreatic function tests. 

  • Chest X-rays. This test uses invisible electromagnetic energy beams to create 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 appropriately. They are usually 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 stool fat absorption.

Online Medical Reviewer: Blaivas, Allen J., DO
Online Medical Reviewer: Holloway, Beth Greenblatt, RN, M.Ed.
Date Last Reviewed: 11/1/2016
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