Genetic testing and screening

Genetic testing includes any type of test that checks a person's DNA. Tests often use a sample of cells or tissue to look for changes in genes, chromosomes, or proteins. These changes can be a sign of a disease or a sign of an increased risk for getting a disease.

Testing may be done to:

• Find out if you carry a gene for an inherited disease, such as cystic fibrosis.
• Find out if your fetus is at risk for a genetic condition such as Down syndrome.
• Find out if you carry a gene that increases your risk for a disease later in life, such as breast cancer.
• Find out if you have an inherited heart disease called hypertrophic cardiomyopathy.
• Check for genetic changes that may affect your treatment for an existing disease.
• Find out if you have inherited gene changes that affect your response to medicines.
• Identify family members, crime suspects, or victims of war or disasters for legal purposes.

Genetic testing for inherited gene changes can be done using almost any cell or tissue from the body. The type of sample needed will depend on the test.

Samples used in tests include:

• A blood sample from a vein. A health professional uses a needle to take a blood sample, usually from the arm.
• A cell sample from the cheek. A swab is used to scrape some tissue from the inside of the cheek.
• A saliva sample. The person being tested spits into a tube.
• A sample of amniotic fluid. This is collected using amniocentesis or chorionic villus sampling.

You do not need to do anything special to prepare for most of these tests. Your doctor will tell you how to prepare if you are having an amniocentesis or chorionic villus sampling.

Talk with your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean.

The information found by a genetic test can have a big impact on your life. So before you have the test, you may want to talk to a genetic counselor or a doctor who specializes in genetics (geneticist). Genetic counseling can help you understand your genetic risks and decide if you want testing.

The results of genetic testing depend on the type of test done. For example, the results may show if you have a genetic condition, how likely it is that you will have a genetic condition in the future, or if you are a carrier for a condition. The results of prenatal genetic screening may show how likely it is that your fetus will have a genetic condition or birth defect.