Identity testing is a method used to determine biological relationships, including 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:

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 a fetus 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. Then the man is 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.