DNA fingerprinting is a test to identify and
evaluate the genetic information—called
DNA (deoxyribonucleic acid)—in a person's cells. It is
called a "fingerprint" because it is very unlikely that any two people would have
exactly the same DNA information, in the same way that it is very unlikely that
any two 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.
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
Why It Is Done
DNA fingerprinting is done to:
- Find out who a person's parents or siblings
are. 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 a battle.
How To Prepare
Tell your doctor if you have had a blood
transfusion within the past 3 months. You do not need to do anything else before you have this test.
Talk to your doctor about any
concerns you have about the need for the test, its risks, how it will be done,
or what the results will mean. 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
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
Blood sample from a heel stick