In the US today, all 50 states screen newborns for cystic fibrosis using a genetic test or a blood test. The genetic test shows whether a newborn has faulty CFTR genes. The blood test shows whether a newborn's pancreas is working properly. If a genetic or blood test suggests that the person has cystic fibrosis, physicians will typically use a sweat test, which measures the amount of salt in the person's sweat, to confirm the diagnosis. The test is usually performed twice, and high salt levels confirm a diagnosis of cystic fibrosis.
For this test, the doctor triggers sweating on a small patch of skin on an arm or leg. He or she rubs the skin with a sweat-producing chemical and then uses an electrode to provide a mild electrical current. Sweat is collected on a pad and analyzed.
Genetic tests may also be used to determine what type of genetic mutation is causing the condition.
Additional tests include:
- Chest x-rays, which can show inflammation or scarring
- Sinus x-rays, which would indicate signs of sinus infection, a complication of cystic fibrosis
- Lung function tests, which measure air intake and outflow and how well the lungs are delivering oxygen to the blood
- Sputum culture, in which a sample of spit is analyzed for bacteria. The presence of Pseudomonas may suggest more advanced cystic fibrosis in need of aggressive treatment
- Prenatal genetic testing, via amniocentesis and chorionic villus sampling, to show whether a fetus has cystic fibrosis