Cystic Fibrosis Diagnosis

Testing Options

Computer screen with genetic testing results displayed
Prenatal testing for genetic mutations. Corbis via Getty Images / Getty Images

If left untreated, cystic fibrosis (CF) causes irreversible damage to the body. The earlier CF is diagnosed, the sooner treatment can begin to prevent the damage and slow the progression of the disease. In the past, people became very ill from cystic fibrosis before a diagnosis could be made. Over the last couple of decades, tests have been developed that allow diagnosis even before the first symptom appears.

Genetic Testing

Genetic testing is the only way to tell if a person carries the cystic fibrosis trait. It is also sometimes done to find out if a person has cystic fibrosis, or to identify which mutations a person with CF has.

Prenatal Testing

Genetic testing can be done prenatally to determine if a baby will be born with cystic fibrosis. If an expectant couple knows or suspects that they might be carriers of the defective gene, they may opt for testing to help them choose whether or not to terminate the pregnancy. If a couple plans to continue the pregnancy the CF diagnosis will be known before birth and the baby will have the benefit of receiving early treatment.

There are two tests that can be done in the prenatal period. Both tests are invasive and carry a small degree of risk that should be discussed with the physician prior to testing.

Chorionic Villus Sampling (CVS): A small amount of tissue is removed from the placenta and sent to a lab to determine if the defective CFTR gene is present.

This test is usually done around the 11th week of pregnancy.

Amniocentesis: A small amount of amniotic fluid is removed with a needle and syringe through the abdomen and sent to a lab to determine if the defective CFTR gene is present. This test is usually done around the 16th week of pregnancy.

Newborn Screening

Newborn screening does not diagnose CF, but a positive result raises a red flag to alert the physician to order further testing.

In the United States, most states now include cystic fibrosis testing in their routine newborn screening tests.

Sweat Test

The sweat test has been the gold standard diagnostic test for CF for many years. The sweat test is a quick, non-invasive, painless test that measures the levels of sodium and chloride excreted in sweat.It is a pretty good indicator of cystic fibrosis but is not foolproof.

Source: Bilton, D (2008).Cystic fibrosis. Medicine. 36, 273-278.