How is cystic fibrosis (CF) diagnosed?

In most cases, CF is diagnosed during childhood. Doctors diagnose CF with a thorough evaluation and by using different tests. These include:

  • Newborn screening: A healthcare provider takes a few drops of blood from a heel prick, usually while the newborn is in the hospital, and places the drops on a special card called a Guthrie card. Tests at a laboratory can diagnose conditions, including CF. Every state in the United States requires the testing of newborns at birth as well as a few weeks later.
  • Sweat test: The sweat test measures the amount of chloride in the body’s sweat, which is higher in people who have CF. In the test, a healthcare provider spreads a chemical called pilocarpine on the patient’s skin, then applies a small amount of electric stimulation to encourage the sweat glands to produce sweat. The provider then collects the sweat in a plastic coil or on a piece of filter paper or gauze. People of any age can have a sweat test. It is not painful and does not use a needle. This is the most conclusive test for CF.
  • Genetic tests: These are performed using a blood sample that is tested for the faulty genes that cause CF.
  • Chest X-rays: X-rays of the chest are used to support or confirm CF if a healthcare provider suspects that a person has the disease. Other forms of testing need to be used to confirm the presence of CF.
  • Sinus X-rays: As with chest X-rays, sinus X-rays can confirm CF in patients who show certain symptoms. Other forms of testing are used along with sinus X-rays.
  • Lung function tests: The most common lung function test uses a device called a spirometer. The patient breathes in completely, then empties the inhaled breath into the mouthpiece of the spirometer.
  • Sputum culture: A healthcare provider takes a sample of a patient's sputum (spit) and tests it for bacteria. Certain bacteria, such as pseudomonas, are most commonly found in people who have CF.

Last reviewed by a Cleveland Clinic medical professional on 06/13/2019.

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