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Identity Testing

Alternate Names

  • parentage testing
  • paternity testing

Definition

Identity testing is a method used to determine biological relationships, including parents,sisters, brothers, and grandparents. It is most often used to establish the identity of a person's biological father, a process known as paternity testing.

Who is a candidate for the test?

Most often the question of paternity comes up when a child is born out of wedlock. Many times inheritance is based on blood relationship.
Candidates for identity testing may include:
  • anyone who has doubts about the identity of his or her father
  • people involved in a dispute about an estate
  • people who were adopted, and want to be tested when they discover a possible biological parent
  • brothers and sisters who were separated early in life and want to prove that they are related to one another
Government agencies may ask for paternity testing when they are enforcing child support laws.

How is the test performed?

Identity testing is done by matching DNA samples taken from different people. If paternity is in question, a child and one or more potential fathers are tested. Each person submits a sample of blood or a scraping of cells from inside the cheek. Paternity testing can be done before a child is born, on cells collected from the unborn child through amniocentesis. It can also be done on tissue collected from someone who has died.
Once a sample is gathered, DNA is extracted from it in a special lab. The DNA from the child is matched with that of the potential fathers. If there are one or more mismatches in the DNA, the individuals are not related. If there are no mismatches, the certainty that the man is the child's father is calculated. When the certainty reaches a very high level, the matching is stopped and the man is then said to be the father within the reasonable limits of testing.
Different DNA labs match different DNA markers. Some labs may even use blood types to screen people before starting DNA testing. DNA labs also use different methods to determine an index, or probability, of paternity. Testing for other relationships follows the same model, but is usually more complicated.

What is involved in preparation for the test?

No preparation is needed for identity testing. It is important, however, to document the chain of custody of specimens and the identity of everyone being tested. Picture IDs, court orders, notarized statements, and fingerprinting may be required. Results will not be reliable if the person being tested has had a blood transfusion within several weeks of the testing.

What do the test results mean?

Being excluded as the father through paternity testing is absolute. Being named as the father, however, is an assumption based on probability. The same can be said for other types of relationships.

Sources

Crow J: The Evaluation of Forensic DNA Evidence. National Academy Press, 1996.

Walker RH: Parentage Testing Accreditation Requirements Manual. American Association of Blood Banks, 1998.

Technical working Group on DNA Analysis Methods: Guidelines for a Quality Assurance Program for DNA Analysis. Crime Laboratory Digest 22: 21-43, 1995.

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