Cystic Fibrosis

Healthcare providers often test for cystic fibrosis during a newborn screening. Providers perform this test with a few drops of blood from your baby’s heel. A lab looks in the blood sample for immunoreactive trypsinogen (IRT), a chemical made in your pancreas. People with CF have higher levels of IRT in their blood. Babies are often tested for IRT shortly after birth and a few weeks later.

Some conditions — like preterm delivery — can raise IRT levels. So, a positive IRT test alone doesn’t mean your baby has CF. If your baby has higher levels of IRT than expected, your healthcare provider will order additional tests to make a final diagnosis.

In about 5% of cases, the newborn screen doesn’t detect elevated IRT levels in someone with CF. Or you may have been born before routine CF screening was available. If you or your child has symptoms of CF, a provider will perform a sweat test and follow up with additional tests as needed.

Tests for cystic fibrosis

• Sweat test. The sweat test measures the amount of chloride in your body’s sweat. Chloride levels in sweat are higher in people who have CF. This is the most conclusive test for CF, but it may be normal in people with atypical CF.
• Genetic tests. A provider tests blood samples for changes in the genes that cause CF.
• Imaging. Providers use imaging, like sinus and chest X-rays, to support or confirm a CF diagnosis. Imaging alone can’t diagnose CF.
• Pulmonary function tests. These tests measure how well your lungs are working.
• Sputum culture. Your healthcare provider takes a sample of your sputum (mucus coughed up from your lungs) and tests it for bacteria. Certain bacteria, such as Pseudomonas, are most commonly found in people who have CF.
• Pancreatic biopsy. This can tell your provider if you have cysts or damage to your pancreas.
• Nasal potential difference (NPD). This test measures the small amount of electrical charge that’s usually present in the lining of your nose. The movement of ions creates this charge. People with CF don’t have as much ion movement because of the way CF affects their ion channels.
• Intestinal current measurement (ICM). A provider takes a sample of rectal tissue to perform this test. A lab uses the sample to measure how much chloride it secretes.