Medical Author: Melissa Conrad Stoppler, MD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
Paternity testing is a laboratory test to determine whether a man is the father of a given child. Modern paternity tests are done using DNA amplification techniques to examine the unique sequences that occur in each individual's DNA. DNA resides in the nucleus of all cells in the body, and except in the case of identical twins (who have identical DNA sequences), each person has unique regions in their DNA. In paternity testing, a variable number (depending upon the laboratory and the required degree of accuracy) of these unique DNA sequences are compared between a man and a child.
DNA testing can definitively exclude that a given man is the father of a particular child, and can also offer highly conclusive evidence of paternity. Results are generally issued as a statement of probability that the man in question is the father of the child. For example, a laboratory may be able to prove that there is a 99.9% (or even much greater) likelihood of paternity in a given case or may state that there is a zero percent probability of paternity.
When paternity tests are done for legal reasons, strict chain-of-custody procedures are employed by the laboratory to ensure that samples are safe and free from tampering. Photos and/or other identifying information may be taken from those to be tested, and samples are stored and transported in tamper-proof packaging. Samples may also not be collected or transported by any of the parties involved in the case.
Since DNA is present in all living cells, various types of specimens are suitable for paternity testing. Samples for genetic testing are often taken by a swab from the inside of the mouth, but blood samples may also be used. A few drops of blood taken from a finger prick are sufficient for the test.
There are no national regulations that cover paternity testing laboratories. Because of this absence of oversight, the quality, thoroughness, interpretation of results, and admissibility of the information in court from different DNA parentage testing laboratories can vary. However, laboratories may elect to become accredited by the American Association of Blood Banks (AABB) for parentage testing. Laboratories that are AABB accredited have undergone inspections to guarantee that their procedures and standards conform to those established by the AABB for parentage testing.