How is Cystic Fibrosis Diagnosed?

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  • Written By: N. Madison
  • Edited By: Niki Foster
  • Last Modified Date: 15 August 2019
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Typically, a person born with cystic fibrosis exhibits symptoms within the first year of life. However, in some cases, symptoms do not become obvious until adolescence. There have even been some cases in which cystic fibrosis wasn’t diagnosed until adulthood. However, when symptoms are present, there are standard tests used to diagnose the disease.

The sweat test is the most commonly used test for diagnosing cystic fibrosis. This test is used to look for abnormally high levels of sodium chloride, or salt, present in an individual’s sweat. The sweat test is performed by causing an area of the skin to sweat by placing a chemical solution called pilocarpine on it and stimulating it with a mild electric current. The sweat is then collected with a gauze pad and analyzed. The sweat test is not painful, but may cause mild discomfort.

The sweat test may be less effective for newborns, because they tend to produce less sweat. Instead, the immunoreactive trypsinogen test (IRT), which involves blood analysis, is performed. Some individuals with cystic fibrosis may have normal levels of salt in their sweat. In such cases, other tests may be used to diagnose cystic fibrosis.


Blood tests are used to detect mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Cheek scraping tests, involving the painless removal of cells, are sometimes used for this purpose as well. Chest x-rays are also used to diagnose cystic fibrosis.

Pulmonary function tests are sometimes used to determine whether or not a person has cystic fibrosis. These tests measure lung function and capacity. Pulmonary function tests typically require the patient to breathe into a specially designed machine.

Sputum culture tests may be included as part of the diagnostic process. In a sputum test, the subject must cough and spit his or her sputum into a cup. The sputum is taken to a laboratory and assessed for the presence of infection.

Stool evaluations and pancreatic function tests are sometimes included in diagnosing cystic fibrosis. Fortunately, cystic fibrosis can be treated. So far, however, there is no known cure.


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