DNA fingerprinting is a test to identify and evaluate the genetic information, called DNA (deoxyribonucleic acid), of a person's cells. It is called a "fingerprint" because it is very unlikely that any 2 people would have exactly the same cellular information, in the same way that it is very unlikely that any 2 people would have exactly the same physical fingerprint. The test is used to determine whether a family relationship exists between two people, to identify organisms causing a disease, and to solve crimes.

Only a small sample of cells is needed for DNA fingerprinting. A drop of blood or the root of a hair contains enough DNA for testing. Semen, hair, or skin scrapings are often used in criminal investigations. See a picture of DNA testing in a criminal investigation.

A person who has DNA fingerprinting done voluntarily usually provides a sample of blood taken from a vein. DNA testing also can be done on cells obtained by a simple mouthwash or a swab of the cheeks inside the mouth, but these methods are not recommended.

Why It Is Done

DNA fingerprinting is done to:

• Determine who a person's parents are (establish paternity). This test also may be used to identify the parents of babies who were switched at birth.
• Solve crimes (forensic science). Blood, semen, skin, or other tissue left at the scene of a crime can be analyzed to help prove whether the suspect was or was not present at the crime scene.
• Identify a body. This is useful if the body is badly decomposed or if only body parts are available, such as following a natural disaster or battle.

How To Prepare

Tell your health professional if you have had a blood transfusion within the past 3 months. No other special preparation is required before having DNA fingerprinting.

Talk to your health professional about any concerns you have about 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?).

How It Is Done

Blood sample from a vein

DNA that is used to establish paternity is collected from a blood sample. The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Apply a gauze pad or cotton ball over the needle site as the needle is removed.
• Apply pressure to the site and then a bandage.

Blood sample from a heel stick