What is Cystic Fibrosis Screening?

Cystic fibrosis screening can refer to any of the several tests that are used to diagnose cystic fibrosis (CF). This disease is caused by a genetic mutation that results in excess mucus secretion, primarily in the lungs, intestines, pancreas and liver. People with this disease have increased susceptibility to lung infections and have a considerably shortened life expectancy. Cystic fibrosis screening can be carried out at several stages of life. It is performed on neonates and children to diagnose the disease and on adults to determine their carrier status.

Recent research suggests that early diagnosis of cystic fibrosis can have significant benefits on the health of a child with the disease. This is because early intervention with medication, physical therapy and nutrition therapy can improve early childhood development and respiratory function. Because of this, many countries recommend that all children undergo cystic fibrosis screening soon after birth.

In the neonatal screening test, a small blood sample is taken from the newborn infant. To test for CF, the blood sample is tested for a substance called immunoreactive trypsinogen. This substance is an enzyme produced in the pancreas. Levels of this enzyme are elevated in newborns with CF. This test typically is repeated at a later date, because false positive and false negative results are not uncommon.

Another cystic fibrosis screening test that might be performed is the chloride sweat test. This test usually is carried out to diagnose an older child who is suspected of having cystic fibrosis. The sweat chloride test is the main diagnostic test used for CF diagnosis. It involves testing a child’s sweat for the presence of substances that are present in abnormal levels on the skin of someone with CF. This abnormality is present because people with CF have abnormal sweat glands.

In someone with normal sweat glands, the glands secrete salt and water, then reabsorb most of the salt. In someone with cystic fibrosis, salt reabsorption is much lower than normal. Someone with CF therefore has more sodium and chloride on their skin after sweating, and this can be detected with the sweat test. During this test, a chemical is applied to the child’s skin to stimulate sweat production, and the skin is then swabbed for testing. The sweat cystic fibrosis screening test normally is carried out at least twice on different days, to ensure that accurate results are obtained.

Cystic fibrosis is a hereditary disease, caused by a mutation in a gene called CFTR. A person with one copy of the mutated gene does not have CF but is said to be a carrier of the disease. If two carriers have a child, there is a 25 percent chance that the child will inherit a copy of the defective gene from both parents. If this happens, the child will have CF. For this reason, many people choose to have cystic fibrosis screening before conceiving a child, particularly if other family members have the disease.

In cystic fibrosis carrier screening, a blood sample is taken and tested for the presence of an abnormal copy of the CFTR. A positive result means that the person being tested is a cystic fibrosis carrier. When both parents are carriers, they are recommended for genetic counseling to discuss their options for having children.