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The Test Sample
What is being tested?
Cystic fibrosis (CF) is an inherited disease that affects mainly the lungs, pancreas, and sweat glands. It leads to the production of thick, sticky mucus and can cause recurrent respiratory infections and impaired function of the pancreas. The CF gene mutation panel detects the common mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene on chromosome 7 to screen for or diagnose CF or to identify carriers of the disease.
Each cell in the human body (except sperm and eggs) has 46 chromosomes (23 inherited from the mother and 23 from the father). Genes on these chromosomes form the body's blueprint for producing proteins that control body functions.
Cystic fibrosis is caused by a mutation in each of the two copies of the CFTR gene (one copy from each parent). Both copies (alleles) of this gene pair must be abnormal to cause CF. If only one copy is mutated, the individual is a CF carrier. Carriers do not generally have any CF symptoms, but they can pass their abnormal CF gene copy on to their children.
To date, more than 2,000 different mutations of the CFTR gene have been identified, but only a few of the mutations are common. The majority of cystic fibrosis cases in the U.S. are caused by a mutation called deltaF508 (F508).
Recommendations by the American College of Medical Genetics (ACMG) and the American College of Obstetricians and Gynecologists (ACOG) have led to the adoption of a standard CF gene mutation panel. It includes 23 of the most common mutations (those with frequencies greater than 0.1% in the general U.S. population).
Some laboratories use expanded panels of up to 100 or more mutations designed to detect rare mutations particular to specific ethnic populations. These may provide slightly better sensitivity to detect mutations in some ethnic populations but are not recommended by ACOG for general screening. Some rare mutations are seen in only a few individuals and may not be detected with routine testing, even with an expanded panel.
In a CF gene mutation panel, the laboratory specifically examines the CFTR gene on each chromosome 7 for the 23 mutations. If the initial panel of mutations demonstrates a single mutation, additional testing for other less common mutations may be indicated if the individual is suspected of having CF.
How is the sample collected for testing?
A blood sample is drawn from an infant's heel by collecting a spot of blood onto filter paper; for older children and adults, a blood sample is obtained by inserting a needle into a vein in the arm. A scraping of the inner cheek, called a buccal swab sample, may be collected. For prenatal testing, a sample of amniotic fluid may be collected using amniocentesis or a chorionic villus sample may be collected.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.