Share this page
Print this article
Was this page helpful?

CF Gene Mutation Testing

Also known as: Cystic fibrosis (CF) genotyping; CF DNA analysis; CF gene mutation panel; Molecular genetic testing
Formal name: Cystic Fibrosis Gene Mutation Panel
Related tests: Sweat chloride; Immunoreactive trypsinogen (IRT); Stool trypsin and chymotrypsin

At a Glance

Why Get Tested?

To detect cystic fibrosis (CF) genetic mutations to establish CF carrier status or to establish the diagnosis of CF in an individual; the American College of Obstetricians and Gynecologists (ACOG) and the American College of Medical Genetics (ACMG) recommend targeted gene screening when a couple is contemplating pregnancy or in early pregnancy

When to Get Tested?

When a newborn infant has meconium ileus or when a person has symptoms of CF (salty sweat, persistent respiratory infections, wheezing, persistent diarrhea, foul-smelling greasy stools, malnutrition, vitamin deficiency, or male infertility); if a person has a positive sweat chloride or IRT test or a close relative who has been diagnosed with CF; when a patient is seen by an obstetrician for pre-conception counseling or an early prenatal visit or is undergoing genetic counseling for available prenatal screening tests and wants to find out their CF carrier status; or for prenatal diagnostic purposes when both parents are known CF carriers

Sample Required?

A blood sample drawn from an infant’s heel, a spot of blood that is put onto filter paper, or a blood sample drawn from a vein in the arm; buccal swab or prenatal (amniocentesis or chorionic villus) specimens may also be used

Test Preparation Needed?

None

The Test Sample

What is being tested?

The CF gene mutation test identifies mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene on chromosome 7. 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 located on chromosomes 7. Both copies (alleles) of this gene must be abnormal to cause CF. If only one copy of the gene pair is mutated, the individual is a CF carrier. Carriers are not ill; they generally do not have any CF symptoms, but they can pass their abnormal CF gene copy on to their children.

To date, more than 1,000 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 as many as 97 mutations designed to pick up more rare mutations particular to specific ethnic populations. The vast majority of rare CF mutations are "private" and unique to a single individual or family.

In CF gene mutation testing, the laboratory specifically examines the CFTR gene on each chromosome 7 for the 23 mutations. If the initial panel of 23 mutations demonstrates a mutation, additional testing for other less common mutations may be indicated if the individual is suspected of having the disease.

How is the sample collected for testing?

A blood sample is drawn from an infant’s heel, a spot of blood is put onto filter paper, or 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, or prenatal (amniocentesis or chorionic villus) specimens may also be used.

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.

The Test

How is it used?

CF gene mutation testing can be done to screen the general population or to screen a targeted (higher risk) subset of the population for carrier status. It can be used to confirm the diagnosis of cystic fibrosis (CF) in a symptomatic patient with an elevated immunoreactive trypsinogen (IRT) or positive sweat chloride test.

The test can be used as part of a prenatal workup, to establish carrier status in prospective parents and therefore to determine the risk CF in their infant. This may be done by sequential testing or couple testing. In a sequential strategy, the mother is usually tested first. If she is not a carrier, then any child she had would, at most, be a carrier from the father’s side. Using this logic, the father is not tested. If she is a carrier, then the father is also tested for carrier status. With couple testing, both parents are tested at the same time. In either case, follow-up genetic counseling is essential to provide couples with information on what it means to be a carrier and to explain the limitations of the testing, including the residual risk of being a carrier even if the test results were negative (e.g., there is still a slight risk that rare mutations, not included in the standard panel, might be present).

CF gene mutation testing can also be used for prenatal diagnosis if both parents are known to be carriers and if their gene mutations have been previously identified. DNA from amniocentesis and chorionic villus sampling procedures, although somewhat invasive, can be used to test the fetus for the known parental mutations.

^ Back to top

When is it ordered?

A doctor may order CF gene mutation testing to rule out CF when a patient has symptoms such as salty sweat, persistent respiratory infections, wheezing, persistent diarrhea, foul-smelling bulky greasy stools, malnutrition, vitamin deficiency, or male infertility.

CF gene mutation testing may be ordered to confirm a CF diagnosis following a positive sweat chloride or IRT test. It may also be ordered as a targeted general population screen, as part of a genetic counseling workup prior to conceiving, or as an “at risk” screen, if, for example, the patient has a close relative who has been diagnosed with CF.

^ Back to top

What does the test result mean?

Diagnostic test results
If the CF gene mutation test is positive - it comes back with two identified gene mutations - then the patient has CF. The test, however, cannot predict how severe or mild the symptoms may be. Patients with the exact same mutations may have very different outcomes.

If the CF gene mutation panel test reveals a single mutation or is negative and the patient is symptomatic, further mutation testing, a sweat chloride test, and/or other laboratory testing to check organ function are warranted. The patient may have a more rare form of CF that has not been identified or may have a lung or pancreatic disease or condition other than cystic fibrosis.

Carrier test results
If the CF gene mutation test comes back with a single identified mutation and the patient is asymptomatic, then chances are that the person is a CF carrier. This may be information some individuals want to know before having children. If you are identified as a carrier, your siblings may also want to verify their carrier status.

If the test comes back negative for mutations and the patient is asymptomatic, chances are that the patient does not have CF and is not a carrier. There is still a slight risk that the person could be a carrier of a rare mutation not identified with the standard panel.

^ Back to top

Is there anything else I should know?

Early detection of CF allows patients to be referred to CF centers for specialized care, individualized treatment plans, and careful monitoring. Beginning treatments such as taking oral enzyme supplements and fat-soluble vitamins, learning how to clear mucus out of airways, and learning to recognize respiratory infections can improve a patient’s quality of life and minimize CF complications.

^ Back to top

Common Questions

1.  Will this CF gene mutation test pick up any other genetic diseases?

No, it is only checking for specific CF mutations. Every genetic disease requires specific DNA testing to identify it (assuming that the gene and mutations causing it are known).

^ Back to top

2.  What is my risk of being a carrier if I am of mixed ethnicity?

Generally, the frequency of CF carriers is highest in Caucasians (1/25), about half that in Hispanic Caucasians and African Americans, and about half that again in Asians. Some ethnic groups, such as individuals of Eastern European Jewish descent, may show CF confined to a very limited number of mutations and may elect to have testing using a limited mutation panel. Since the ethnicity of the U.S. population is becoming increasingly blended, the historical data and statistical risks are changing. Quoted risks based on ethnicity are estimates, and the risk for individuals of mixed ethnicity may be unknown. Some families may also carry the additional risk of specific rare mutations within their family line.

^ Back to top

3.  What are the advantages of the DNA-based blood test over other CF screening tests?

Generally, the DNA-based mutation test is much more specific than other screening tests, which may yield abnormal results for non-CF reasons. Also, these other screening tests may be restricted as to when they can be applied (for example, newborns can not be tested with sweat chloride until about two months of age). Furthermore, DNA-based testing is the only reliable means of identifying carriers of CF mutations, and it is in this capacity that the testing is being most widely applied.

^ Back to top

4.  Does the state require or offer newborn screening for CF? Do I need to request it?

Most states offer CF testing as part of their newborn screening tests, but screening requirements vary from state to state, as determined by individual state public health departments. All states now have their own mandatory newborn screening programs, but in some states, the screening for CF is not mandatory, so you may need to request it.

^ Back to top

Ask a Laboratory Scientist

This form enables you to ask specific questions about your tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. If your questions are not related to your lab tests, please submit them via our Contact Us form. Thank you.

* indicates a required field




  Patient, Family member or Friend
  Laboratorian or Other Medical Professional
  Other



You must provide a valid email address in order to receive a response.



| Read The Disclaimer


Spam Prevention

| |

Article Sources

« Return to Related Pages

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

(Update April 23, 2008) National Newborn Screening and Genetics Resources Center. National Newborn Screening Status Report. Available online at http://genes-r-us.uthscsa.edu/nbsdisorders.htm through http://genes-r-us.uthscsa.edu. Accessed January 2009.

American College of Obstetricians and Gynecology (ACOG). Cystic fibrosis Carrier Testing: The Decision is Yours. Available online at http://www.acog.org/from_home/wellness/cf001.htm through http://www.acog.org. Accessed January 2009.

(February 19, 2008) American Medical Association. Cystic fibrosis testing (including recommendations by ACMG and ACOG). Available online at http://www.ama-assn.org/ama/pub/category/9181.html through http://www.ama-assn.org. Accessed January 2009.

Human Genome Project Information. Genetic Disease Profile: Cystic Fibrosis. Available online at http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/cf.shtml through http://www.ornl.gov. Accessed January 2009.

(November 17 2008) MedlinePlus Medical Encyclopedia. Cystic Fibrosis. Available online at http://www.nlm.nih.gov/medlineplus/cysticfibrosis.html. Accessed January 2009.

(July 2008) National Heart, Lung, Blood Institute. Cystic Fibrosis, How Is Cystic Fibrosis Diagnosed? Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/cf/cf_diagnosis.html through http://www.nhlbi.nih.gov. Accessed January 2009.

Denise I. Quigley, PhD, FACMG. Co-Director Cytogenetics/Molecular Genetics, Airport Way Regional Laboratory, Portland, OR.

Peter Jacky, PhD, FACMG. Director of Cytogenetics and Molecular Genetics, Airport Way Regional Laboratory, Portland, OR.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

NIDDK (July 1997). Cystic Fibrosis Research Directions. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) [NIH Publication No. 97-4200]. Available online at http://www.niddk.nih.gov/health/endo/pubs/cystic/cystic.htm through http://www.niddk.nih.gov.

Cystic Fibrosis Foundation. Sweat Testing Procedure and Commonly Asked Questions. [On-line information]. Available online at http://www.cff.org/publications01.htm through http://www.cff.org.

Tait, J., et. al. (26 March 2001). Cystic Fibrosis. GENEReviews [On-line information]. Available online at http://www.genetests.org/.

Mayo Clinic (2001, February 09). What is Cystic Fibrosis? Mayo Clinic [On-line information]. Available online at http://www.mayoclinic.com/invoke.cfm?objectid=2CEBF76F-D36A-4D15-B937BFF91AB51438 through http://www.mayoclinic.com.

MEDLINEplus (2002, January 2, Updated). Cystic Fibrosis. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000107.htm.

MEDLINEplus (2002, January 2, Updated). Sweat Electrolytes. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003630.htm.

MEDLINEplus (2002, January 2, Updated). Trypsin and chymotrypsin in stool. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003594.htm.

Mountain States Genetics (1999, September, Revised). Cystic Fibrosis (CF). Newborn Screening Practitioner’s Manual [On-line information]. Available online at http://www.mostgene.org/pract/prac26.htm through http://www.mostgene.org.

National Institutes of Health (1995, November). Facts About Cystic Fibrosis. National Heart, Lung, and Blood Institute NIH Publication No. 95-3650 [On-line information]. Available online at http://www.nhlbi.nih.gov/health/public/lung/other/cf.htm through http://www.nhlbi.nih.gov.

Quest Diagnostics NEWS (2002, Winter). What is the Best Test to Screen for Cystic Fibrosis? [On-line serial]. PDF available for download at http://www.questdiagnostics.com/hcp/files/02winter_newsletter.pdf through http://www.questdiagnostics.com.

MEDLINEplus (2002, January 2, Updated). Neonatal cystic fibrosis screening. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003409.htm.

Drkoop (2001). Cystic fibrosis. Medical Encyclopedia [On-line information]. Available online at http://www.drkoop.com/conditions/ency/article/000107.htm through http://www.drkoop.com.

MEDLINEplus (2002, January 2, Updated). Trypsinogen. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003560.htm.

Biomedical Hypertext (1999 May 20, last update). Exocrine Secretions of the Pancreas. Colorado State University [On-line information]. Available online at http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pancreas/exocrine.html through http://arbl.cvmbs.colostate.edu.

UPCMD (1998 – 2002). Cystic Fibrosis. University Pathology Consortium, LLC [On-line information]. Available online at http://www.upcmd.com/dot/examples/00218/description.html through http://www.upcmd.com.

Sainato, D., (2002, March). Genetic Testing for CF Going Mainstream? Clinical Laboratory News [Journal], Vol 28.

Peter Jacky, PhD, FACMG. Director of Cytogenetics and Molecular Genetics, Airport Way Regional Laboratory, Portland, OR.