A genetic test examines a DNA (deoxyribonucleic acid) sample of a person's cells for abnormal genes, or analyzes the number, arrangement, and characteristics of the chromosomes. Testing may be performed on samples of blood, semen, urine, saliva, stool, body tissues, bone, or hair.

You inherit half of your genetic information from your mother and the other half from your father. Genes, alone or in combination, determine what features (genetic traits) a person inherits from his or her parents, such as blood type, hair color, eye color, and other characteristics, including risks of developing certain diseases. Certain changes in genes or chromosomes may cause medical problems.

Why It Is Done

A genetic test is done to:

• Determine if people who have a family history of a specific disease are likely to pass that disease on to their children (carrier identification). Information obtained from this type of testing can help guide a couple as they make decisions regarding pregnancy.
• Determine if a fetus has a disorder, such as Down syndrome (prenatal testing). Information obtained from this type of testing can help guide a couple as they make decisions regarding pregnancy.
• Check for various metabolic diseases, such as phenylketonuria (PKU) (newborn screening). Information obtained from newborn screening can help guide medical treatment to ensure the best possible outcome for the baby.
• Determine if you carry a genetic change that increases your risk for developing a disease, such as breast cancer or Huntington's disease, later in life (late-onset disease testing). This might be important to you if you have a parent or other relative diagnosed with the disease. Information obtained from this type of testing can help you make decisions about disease prevention or future childbearing.

How To Prepare

No special preparation is needed before having this test.

Talk to your health professional about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will indicate. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

Since the information obtained from a genetic test can have a profound impact on your life, you may want to see a doctor who specializes in genetics (geneticist) or a genetic counselor. This type of counselor is trained to help you understand your risk for developing a genetic disease or having a child with an inherited (genetic) disease, such as sickle cell disease, cystic fibrosis, or hemophilia. A genetic counselor can help you make well-informed decisions. Ask to have genetic counseling before making a decision about genetic testing.

How It Is Done

A genetic test can be done using almost any cell or tissue from the body.

Blood sample from a heel stick