Genetic testing can be used to find out whether a person is carrying a specific genetic mutation (altered gene) that causes a particular medical condition.

It may be carried out for a number of reasons, including:

• diagnosing a person with a genetic condition
• helping work out the chances of a person developing a particular condition
• determining if a person is a carrier of a certain genetic mutation that could be inherited by any children they have

You will usually need to get a referral from your GP, or a specialist doctor if you have one, for genetic testing to be carried out – speak to your GP or your doctor about the possibility of testing if you think you may need it.

What does genetic testing involve?

Genetic testing usually involves having a sample of your blood or tissue taken. The sample will contain cells containing your DNA and can be tested to find out whether you are carrying a particular mutation and are at risk of developing a particular genetic condition.

In some cases, genetic testing can be carried out to see if a foetus is likely to be born with a certain genetic condition by testing samples of amniotic fluid (the fluid that surrounds the foetus in the womb) or chorionic villi cells (cells that develop into the placenta) extracted from the mother's womb using a needle.

Depending on the condition(s) being tested for, the blood or cell samples will then be tested and examined in a genetics laboratory to check for a specific gene, a certain mutation on a specific gene or any mutation on a specific gene.

In some cases, it may be necessary to check an entire gene for mutations, using a process called gene sequencing. This has to be done very carefully, and it can take a long time compared to most other hospital laboratory tests.

Depending on the specific mutation being tested for, it can take weeks or even months for the results of genetic tests to become available. This can be because the laboratory has to gather information to help them interpret what has been found. 

It is also important to realise that it is not always possible to give definite answers after genetic testing. Sometimes it is necessary to wait to see if the person being tested or other relatives do, or do not develop a condition, and other tests may need to be performed.

You can find out more about genetic testing and how it is carried out by reading the leaflet: 'What happens in a genetics laboratory?' (PDF, 1.90Mb).

Genetic counselling

If your doctor thinks genetic testing may be appropriate in your case, you will usually be referred for genetic counselling as well.

Genetic counselling is a service that provides support, information and advice about genetic conditions. It is conducted by healthcare professionals who have been specially trained in the science of human genetics (a genetic counsellor or a clinical geneticist).

What happens during genetic counselling will depend on exactly why you've been referred. It may involve:

• learning about a health condition that runs in your family, how it's inherited and which family members may be affected
• an assessment of the risk of you and your partner passing an inherited condition on to your child
• a look at the medical history of your family or your partner's family and drawing up a family tree
• support and advice if you have a child affected by an inherited condition and you want to have another child
• a discussion about genetic tests, which can be arranged if appropriate – including the risks, benefits and limitations of genetic testing
• help in understanding the results of genetic tests and what they mean
• information about relevant patient support groups

You will be given clear, accurate information so you can decide what's best for you.

Your appointment will usually take place at your nearest NHS regional genetics centre. The British Society for Genetic Medicine has details for each of the genetics centres in the UK.