CF Gene Mutation Testing

Also known as: Cystic fibrosis (CF) genotyping; CF DNA analysis; CF gene mutation panel; molecular genetic testing

Related tests: Sweat chloride, Immunoreactive trypsin (IRT)

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

When to Get Tested?

When a newborn baby has no stools in the first 24 to 48 hours of life (meconium ileus) or when a person has symptoms of CF; if a person has a positive sweat chloride or an immunoreactive trypsin test or a close relative who has been diagnosed with CF; or when a patient is undergoing genetic counselling and wants to find out if they are a CF carrier. In addition, high risk carrier couples may have the test prior to in vitro fertilization so that the test can be carried out before implantation.

Sample Required?

A blood sample taken from an infant's heel; a spot of blood that is put onto filter paper; or a blood sample taken from a vein in the arm

The Test Sample

What is being tested?

The CF gene mutation test identifies mutations in the CFTR gene. 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 a pair of genes 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 patient will be a carrier. Carriers are not ill, they do not have any symptoms, but they can pass their abnormal CF gene copy on to their children.

So far, over 1500 different mutations of the chromosome 7 gene have been identified, but only a few of the mutations are common. The majority of CF in the UK is caused by a mutation called deltaF508.

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

How is the sample collected for testing?

A blood sample is taken 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.

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.

The Test

How is it used?

CF gene mutation testing is used to confirm the diagnosis of Cystic fibrosis (CF) in a symptomatic patient with an elevated IRT or sweat chloride test.

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When is it requested?

A doctor may use CF gene mutation testing to rule out a diagnosis of CF if the patient has symptoms such as salty sweat, continuous lung infections, wheezing, persistent diarrhoea, foul-smelling bulky greasy stools, malnutrition, and vitamin deficiency.

CF gene mutation testing may also be used to confirm a CF diagnosis following a positive sweat chloride or IRT test.

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What does the test result mean?

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 tell how severe or mild the symptoms may be. Patients with the exact same mutations may have very different outcomes.

If the test comes back negative for mutations and the patient does not have symptoms, it is likely that they do not have CF and are not a carrier. There is still a slight risk that the person could be a carrier of a rare mutation not picked up with the standard tests.

If the CF gene mutation test is negative and the patient has symptoms, the doctor may recommend further genetic testing, a sweat chloride test, and other laboratory testing to check organ function. The patient may have a more rare form of CF that is not being identified or may have a lung or pancreatic disease or condition other than cystic fibrosis.

If the CF gene mutation test comes back with a single identified mutation and the patient does not have symptoms, then the 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, then brothers or sisters may also want to check their carrier status.

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Is there anything else I should know?

Early detection of CF allows patients to be referred to specialist care. 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.

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Common Questions

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

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

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

Since the ethnicity of the UK population is becoming increasingly blended, the historical data and statistical risks are changing. Your risk will be an unknown mix of your inherited ethnic risk. Some families may also carry the additional risk of specific rare mutations within their family line.

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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.