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Page: Diagnosis and Monitoring
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Cystic fibrosis may be diagnosed by newborn screening, sweat testing, or genetic testing. As of 2006 in the United States, ten percent of cases are diagnosed shortly after birth as part of newborn screening programs. The newborn screen identifies decreased amounts of the enzyme trypsin. However, most states and countries do not screen for CF routinely at birth. Therefore, most individuals are diagnosed after symptoms prompt an evaluation for cystic fibrosis. The most commonly used form of testing is the sweat test. Sweat testing involves application of a medication that stimulates sweating (pilocarpine) to one electrode of an apparatus and running electric current to a separate electrode on the skin. This process, called iontophoresis, causes sweating; the sweat is then collected on filter paper or in a capillary tube and analyzed for abnormal amounts of sodium and chloride. People with CF have increased amounts of sodium and chloride in their sweat. CF can also be diagnosed by identification of mutations in the CFTR gene.
A multitude of tests is used to identify complications of CF and to monitor disease progression. X-rays and CAT scans are used to examine the lungs for signs of damage or infection. Examination of the sputum under a microscope is used to identify which bacteria are causing infection so that effective antibiotics can be given. Pulmonary function tests measure how well the lungs are functioning, and are used to measure the need for and response to antibiotic therapy. Blood tests can identify liver problems, vitamin deficiencies, and the onset of diabetes. DEXA scans can screen for osteoporosis and testing for fecal elastase can help diagnose insufficient digestive enzymes.
Prenatal diagnosis
Couples who are pregnant or who are planning a pregnancy can themselves be tested for CFTR gene mutations to determine the likelihood that their child will be born with cystic fibrosis. Testing is typically performed first on one or both parents and, if the risk of CF is found to be high, testing on the fetus can then be performed. Cystic fibrosis testing is offered to many couples in the US. The American College of Obstetricians and Gynecologists recommends testing for couples who have a personal or close family history of CF as well as couples at high risk because of their ethnicity.
Because development of CF in the fetus requires each parent to pass on a mutated copy of the CFTR gene and because CF testing is expensive, testing is often performed on just one parent initially. If that parent is found to be a carrier of a CFTR gene mutation, the other parent is then tested to calculate the risk that their children will have CF. CF can result from more than a thousand different mutations and, as of 2006, it is not possible to test for each one. Testing analyzes the blood for the most common mutations such as ?F508 — most commercially available tests look for 32 or fewer different mutations. If a family has a known uncommon mutation, specific screening for that mutation can be performed. Because not all known mutations are found on current tests, a negative screen does not guarantee that a child will not have CF. In addition, because the mutations tested are necessarily those most common in the highest risk groups, testing in lower risk ethnicities is less successful because the mutations commonly seen in these groups are less common in the general population.
Couples who are at high risk for having a child with CF will often opt to perform further testing before or during pregnancy. In vitro fertilization with preimplantation genetic diagnosis offers the possibility to examine the embryo prior to its placement into the uterus. The test, performed 3 days after fertilization, looks for the presence of abnormal CF genes. If two mutated CFTR genes are identified, the embryo is excluded from embryo transfer and an embryo with at least one normal gene is implanted.
During pregnancy, testing can be performed on the placenta (chorionic villus sampling) or the fluid around the fetus (amniocentesis). However, chorionic villus sampling has a risk of fetal death of 1 in 100 and amniocentesis of 1 in 200, so the benefits must be determined to outweigh these risks prior to going forward with testing. Alternatively, some couples choose to undergo third party reproduction with egg or sperm donors.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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