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