By FindLaw Staff | Reviewed by Hal Armstrong, Esq | Last updated December 16, 2021
Paternity can be determined by highly accurate tests conducted on blood or tissue samples of the father (or alleged father), mother, and child. These tests have an accuracy range of between 90 and 99 percent. They can exclude a man who is not the biological father, and can also show the likelihood of paternity if he’s not excluded. These tests have a significant legal impact when it comes to establishing child custody and support.
In a contested paternity case, a party must submit to genetic tests at the request of any other party. If the father could be one of several men, each may be required to take a genetic test to determine paternity. There are several different ways to establish whether an alleged father is the natural and legal father of the minor child, such as the use of paternity blood tests and DNA paternity tests.
Paternity Blood Tests
Paternity blood tests were first performed in the middle half of the twentieth century, by comparing blood types of tested parties. This involved isolation of blood sera from antigen-challenged individuals that did not possess certain red blood cell antigens. These antigens are protein molecules that may be combined with sugar molecules, and reside in the red blood cell membrane. These sera cause coagulation of red blood cells in individuals that possess that particular red blood cell antigen.
In the ABO blood typing system, humans can possess the A antigen (A blood type), the B antigen (B blood type), both the A and B antigen (AB blood type), or neither of these antigens (O blood type). Red blood cell antigen systems of this sort can be used for paternity blood testing because there are genes that code for the antigens and these are inherited genes.
A mother who has Type B blood and a father who has Type O blood could not have a child who has type AB blood. The true father of the child must have the gene for the A antigen. Using RBC antigen systems for paternity blood testing did not provide for a very powerful test because the frequencies of the genes that coded for the antigens are not very low.
In the 1970s a more powerful test was developed using white blood cell antigens or Human Leukocyte Antigens (HLA), resulting in a test that was able to exclude about 95 percent of falsely accused fathers. Several milliliters of blood are required to perform the test.
Blood types alone cannot be used to determine who the father is, but they can be used to determine the biological possibility of fatherhood.
