Diagnosis of Cystic Fibrosis

Diagnosis of Cystic Fibrosis

How is cystic fibrosis diagnosed?

In addition to a complete medical history and physical examination, diagnostic steps for cystic fibrosis may include:

  • Sweat (chloride) test—a test to measure the amount of chloride in the sweat. The test is performed by placing a solution on the forearm (or the thigh if the 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 your child. The sweat is collected onto a gauze pad and analyzed. Higher than normal amounts of chloride may suggest cystic fibrosis. The sweat test is not painful and usually causes only minor discomfort. The test is difficult to perform accurately and is only reliable when performed at a lab associated with a CF Foundation accredited care center.
  • Genetic test—a blood sample or cells scraped from the cheek may be obtained to test for mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene.
  • Blood test—blood tests can assess infection and involvement of certain organs (e.g., liver).
  • X-ray—a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones and organs onto film.
  • Pulmonary function test—diagnostic test that helps to measure the lungs' ability to move air appropriately. The tests are usually performed with special machines into which a child must breathe.
  • Sputum culture—a diagnostic test performed on the material that is coughed up from the lungs and into the mouth. A sputum culture is performed to determine what bacteria are present in the airways. Young children who cannot cough up sputum may have their throats swabbed to look for these bacteria.
  • Stool evaluation—measures stool fat absorption.
  • Pancreatic function tests—measures the ability of the pancreas to respond to the hormone secretin (a hormone made in the glands of the small intestine).