What is the Combined Paternity Index?

The Combined Paternity Index (CPI) is derived from the Paternity Indices obtained for each genetic locus tested. The CPI represents the likelihood of Paternity and is calculated on the basis of the how common is the genetic information found in your analysis with the general population. The CPI can result in a 99.99%+ Probability of Paternity. Both the CPI and the Probability of Paternity are quoted in the results of the DNA Paternity tests performed.

The DNA test report in more detail

The DNA obtained from the swabs sent by the client is used to locate certain regions of chromosomes that vary in length between individuals. Each of these sites is called a locus and our DNA test is based on sixteen of these loci. Studies of these specific loci have shown that there are many different size fragments (alleles) associated with each locus in a large population.

The DNA test report will show on the left hand column each of the 21 loci involved in the test. Each individual has two copies of a chromosome, one inherited from each parent. For each loci, two numbers are presented (or one in the case where the alleles are identical (homozygous) representing the size of the allele. These numbers are then matched between the people involved in the testing.

So, for example, if a child has two alleles labelled as 16 and 19, and the mother has two alleles labelled 16 and 18, then the child will have inherited the 16 allele from the mother and the allele 19 from the father. Therefore the alleged father being tested for paternity confirmation must have this allele if he is to be confirmed as the biological father. This process of comparison is performed for each loci tested. If the alleged father does not have the matching allele at every locus tested, then he cannot be confirmed as the biological parent.

As explained above, a Paternity Index is obtained for each locus and the combined CPI is used to calculate the probability of relationship, which is the percentage likelihood that a man with the alleles of the alleged father is the biological parent of the child, as compared to an untested, unrelated man of the same race. This Probability Percentage is presented in the results.

If the Probability Percentage is 0% this will mean that the DNA of the alleged father is not consistent with that of the child and therefore he is excluded as the biological father. If the probability Percentage is consistent, then a result in excess of 99.9%+ is normally obtained.

Amelogenin sex gene

It is also important to note that one of the loci tested, labelled as Amelogenin, is used to confirm the sex of the person. This is important in a paternity test as a first confirmation that the samples provided by client reflects the sex indicated in the submission forms.

Also all tests performed through non-standard or forensic samples such as hair, semen etc do not change the result presentation of the test result since once the DNA is successfully extracted, the testing process is similar to the standard swab analysis.

If you have any problems interpreting your paternity test result, contact our customer support team.