How is cystic fibrosis (CF) diagnosed?

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: Your healthcare provider takes a few drops of blood from a heel prick, usually while your newborn is in the hospital, and places the drops on a special card called a Guthrie card. The screening looks for a list of conditions, including CF. Every U.S. state requires the testing of newborns at birth and 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, your healthcare provider spreads a chemical called pilocarpine on your skin, then applies a small amount of electric stimulation to encourage the sweat glands to produce sweat. Your 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’s not painful and does not use a needle. This is the most conclusive test for CF.
• Genetic tests: Blood samples are tested for the genes that cause CF.
• Chest X-rays: Your healthcare provider will order X-rays of the chest are used to support or confirm CF, but a chest X-ray isn’t the only test needed to confirm a diagnosis. Other tests must be done.
• Sinus X-rays: As with chest X-rays, sinus X-rays can confirm CF in people 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. You breathe in completely, then push the inhaled breath into the mouthpiece of the spirometer.
• Sputum culture: Your healthcare provider takes a sample of your sputum (spit) and tests it for bacteria. Certain bacteria, such as Pseudomonas, are most commonly found in people who have CF.
• Nasal potential difference (NPD): This test uses a voltmeter and electrodes placed in two places in your nose and one place outside of your nose to measure the electricity generated by the transfer of ions in solution across the nasal tissue. The test uses three different types of solutions.
• Intestinal current measurement (ICM): You’ll have to have a biopsy of rectal tissue for this test. The tissue is made to secrete chloride, which is then measured.

In people who have atypical cystic fibrosis, the sweat test may be normal in terms of the levels of chloride. Some people with atypical CF may have been born before testing became routine. Your provider may order NPD and ICM tests when the diagnosis is questionable.