Cystic fibrosis carrier detection
What is this test?
This test detects mutations in the cystic fibrosis transmembrane regulator (CFTR) gene. This genetic test is used to help screen for cystic fibrosis. A sample of blood, buccal cells, or chorionic villus may be collected for this test.
What are other names for this test?
- Cystic fibrosis DNA detection
- Cystic fibrosis mutation analysis
What are related tests?
- Serum immunoreactive trypsin measurement
Why do I need this test?
Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. The following is a possible reason why this test may be done:
- Cystic fibrosis screening
When and how often should I have this test?
When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.
Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.
The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.
How should I get ready for the test?
Before having blood collected, tell the person drawing your blood if you are allergic to latex. Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. Also tell the healthcare worker if you have felt nauseated, lightheaded, or have fainted while having blood drawn in the past.
There is no preparation needed for this test.
CVS is a procedure that requires your written consent. Review the consent form with the healthcare worker and ask any questions that you have before signing the consent form. Tell the person doing the CVS if you have a history of pregnancy difficulties, such as premature (early) labor, incompetent cervix (a weak or failing cervix), placenta previa (a placenta that is abnormally low, near or over the cervix), abruption placentae (the placenta is separate from the uterine wall too early), and if you are Rh negative (Rh incompatibilities happen when a baby’s blood has a protein that the mother does not, thus causing an immune reaction). Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. You should also report if you have a history of allergic or other reactions to local anesthetics. Depending on method used to do the CVS, you may be asked to drink extra fluids and have a full bladder for the procedure.
How is the test done?
A sample of venous blood, buccal cells, or chorionic villus may be collected for this test.
When a blood sample from a vein is needed, a vein in your arm is usually selected. A tourniquet (large rubber strap) may be secured above the vein. The skin over the vein will be cleaned, and a needle will be inserted. You will be asked to hold very still while your blood is collected. Blood will be collected into one or more tubes, and the tourniquet will be removed. When enough blood has been collected, the healthcare worker will take the needle out.
Buccal cells are cells from the inner lining of the cheek or mouth. To collect a sample of buccal cells, you will need to open your mouth wide. A special brush or swab will be rotated rapidly up and down on your inner cheeks for 30 seconds. Do not close your mouth when the sample is being collected. After the sample has been collected, the brush or swab will be taken out and tested.
The chorionic villus is a part of the placenta (the organ that nourishes the baby during pregnancy). A sample of chorionic villus is collected by a procedure called chorionic villus sampling (CVS). Depending on the location of your placenta, CVS may be done either through your cervix (transcervically) or abdomen (transabdominally). Both methods will require you to lie down and will use ultrasound to assist the sample collection. For a transcervical CVS, you will be in a position similar to a Pap smear. A speculum will be used to gently spread apart your vagina. Your cervix or vagina will be cleaned with an antiseptic solution. A flexible catheter will be placed through your cervix and a small sample removed. For the transabdominal method, a needle will be used to go through the abdominal wall into the placenta. This will allow a syringe to draw out a small sample of placenta.
If a transabdominal method is used, you will be asked to lie on your back. An area of skin on your abdomen will be cleaned with an antiseptic solution, and a sterile area prepared. You will be given anesthetic to numb your skin. When the area is numb, a needle will be placed through your skin and into the placenta. A small sample of the placenta will be collected and the needle will be withdrawn. All CVS procedures may need to be repeated to collect a sufficient sample size.
How will the test feel?
The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.
This test usually causes no discomfort.
During a blood draw, you may feel mild discomfort at the location where the blood sample is being collected.
During a transcervical CVS procedure, you may feel mild cramping in your abdomen or pelvic area. Before a transabdominal or transcervical CVS procedure, a local anesthetic is given to the procedure site to numb the area. You may feel mild discomfort or stinging when the numbing medicine is injected. As the procedure needle or catheter is inserted through the abdomen or cervix, you may feel some discomfort and pressure. You may feel mild cramping in your abdomen and pelvic area during the procedure. The procedure site may be sore for several days.
What should I do after the test?
After a blood sample is collected from your vein, a bandage, cotton ball, or gauze may be placed on the area where the needle was inserted. You may be asked to apply pressure to the area. Avoid strenuous exercise immediately after your blood draw. Contact your healthcare worker if you feel pain or see redness, swelling, or discharge from the puncture site.
There are no special instructions to follow after this test.
After all CVS procedures, ultrasound and fetal monitoring may be done immediately after the procedure. If a needle was used, pressure may be held to the site until the bleeding or drainage has stopped. A bandage will be placed over the site if a transabdominal method was used. After all CVS procedures, rest is necessary. Do not have sexual intercourse, douche, and avoid heavy lifting for at least 24 hours after all the procedures.
Contact your healthcare worker if there is redness, swelling, pus, drainage, or pain at the procedure site if the transabdominal method was used. For all procedure methods, alert your healthcare worker immediately should you develop a fever; bleeding (heavier than light spotting), fluid leakage or discharge from your vagina; or severe abdominal cramping or pain. An ultrasound is usually done 2 to 4 days after the CVS to make sure that the fetus is doing well.
What are the risks?
Blood: During a blood draw, a hematoma (blood-filled bump under the skin) or slight bleeding from the puncture site may occur. After a blood draw, a bruise or infection may occur at the puncture site. The person doing this test may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of this test.
Buccal cells: A buccal cell collection is generally considered safe. Talk to your healthcare worker if you have questions or concerns about the risks of this test.
Placental tissue (chorionic villus): A placental tissue sample is collected by a procedure called chorionic villus sampling (CVS). Depending on where your placenta is located, different methods may be used. CVS risks, depending on the method, include bleeding and infection at the site. If you have a medical condition, or are using a medication or supplement that causes excessive bleeding, you are at a higher risk of bleeding from the puncture site. It is possible that the needle or catheter that is used to collect the tissue will injure the baby. You may develop a fever, an abnormal vaginal discharge, abdominal pain or cramping, or go into labor. If there is a possibility that you and your baby are not Rh compatible, you may need additional treatment to avoid further complications. There is a risk that your baby will not survive the procedure, or may be adversely affected by this procedure. It is possible that the baby’s limbs, fingers, and toes may be affected by this procedure. The chances of these risks vary depending on your health status, how long you have been pregnant before the CVS procedure, and other factors. The person doing this test may need to perform it more than once. Talk with your healthcare worker if you have any concerns about the risks of having CVS.
What are normal results for this test?
Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following is considered to be a normal result for this test:
What follow up should I do after this test?
Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.
After a CVS procedure, it may take from 1 to 4 weeks to receive results. There is a possibility that you may need an amniocentesis if the CVS was not successful.
Where can I get more information?
- Tomaiuolo R, Spina M, & Castaldo G: Molecular diagnosis of cystic fibrosis: comparison of four analytical procedures. Clin Chem Lab Med 2003; 41(1):26-32.
- Tietz NW (Ed): Clinical Guide to Laboratory Tests, 3rd ed. W. B. Saunders, Philadelphia, PA, 1995.
- Comeau AM, Parad RB, Dorkin HL, et al: Population-based newborn screening for genetic disorders when multiple mutation DNA testing is incorporated: a cystic fibrosis newborn screening model demonstrating increased sensitivity but more carrier detections. Pediatrics 2004; 113(6):1573-1581. Available from URL: http://pediatrics.aappublications.org/cgi/reprint/113/6/1573?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&searchid=1112043248472_15579&stored_search=&FIRSTINDEX=0&sortspec=relevance&volume=113&firstpage=1573&journalcode=pediatrics.
- Lyon E & Miller C: Current challenges in cystic fibrosis screening. Arch Pathol Lab Med 2003; 127(9):1133-1139. Available from URL: http://arpa.allenpress.com/pdfserv/10.1043%2F1543-2165(2003)127%3C1133:CCICFS%3E2.0.CO%3B2.
- Parad RB: Buccal cell DNA mutation analysis for diagnosis of cystic fibrosis in newborns and infants inaccessible to sweat chloride measurement. Pediatrics 1998; 101(5):851-855.
- Super M, Ivinson A, Schwarz M, et al: Clinic experience of prenatal diagnosis of cystic fibrosis by use of linked DNA probes. Lancet 1987; 2(8562):782-784.