DECEMBER 3, 2024

How To Read a Paternity Test

Opening your paternity test report and seeing a page full of numbers and unfamiliar scientific terms can feel overwhelming, especially when the answer means so much to you and your family. Knowing how to read a paternity test ahead of time makes getting results a lot less stressful. Below, we walk through exactly what each part of your report means, in plain language.

DNA Diagnostics Center (DDC) is the world leader in at-home DNA paternity testing, performing over one million paternity tests each year. Every test is processed at our accredited, state-of-the-art laboratory outside Cincinnati, and your results are typically available through our secure online portal in as little as 24 to 48 hours after your samples reach our lab and go into testing.

Your report uses both scientific and legal language to describe our highly precise process. What follows is a straightforward breakdown of each section and what it means for you.

DDC Paternity Tests Results Report Overview

Your DDC paternity test results report contains the following main sections, with each displaying important information.

• Genetic System Table (Locus/Allele Sizes chart)
• Combined Paternity Index
• Probability of Paternity
• Test Conclusions

1. Genetic System Table

DDC’s laboratory tests at least 20 different locations on your DNA, as listed in the “locus” column, and compares them with the same locations on the other tested parties. Each child inherits one copy of this DNA segment from the mother, and one copy from the father. These DNA segments are called “alleles”. Our proprietary technology determines the length of each participant’s alleles and compares them with the lengths of the alleged father’s alleles to determine the number of matches. If the mother participates, the mother’s alleles will also be compared. In the example below, the child shown has two sets of alleles at each location tested, and you can see that at least one of these matches with the alleged father’s alleles.

Note: Colored markings are for illustrative purposes only and are not included on actual reports.

Using statistics, the Paternity Index (listed as PI in the table in the upper left) indicates the strength of the match at each Locus (DNA location). In most cases, at least one of the child’s alleles at each location must match one of the father’s at that location. In addition, the DNA location that shows a participant’s sex (male or female), called the Amelogenin locus, is also tested. This is listed at the bottom of the table. One X means female, while one X and one Y means male. Sometimes additional locations on your DNA must be tested to strengthen the results – for example, when two possible fathers are relatives. In this case, those are also listed. When a child has two alleles that are the same size, it will show as just one number on the table. For example, in the first locus in this example, the child received a “16” from both parents.

2. Combined Paternity Index

The Combined Paternity Index is the number on the lower left side of the report (in the Interpretation section), directly under the Genetic System Table. If you are considered the biological father, there is a number listed for the Combined Paternity Index. If you are not considered the biological father, the report shows “0.” The Combined Paternity Index is an odds ratio indicating how many times more likely it is that the possible father is the biological father than a randomly-selected unrelated man with a similar racial background. In the example shown above, this man is 533,475 times more likely to be the biological father. This number varies on a case by case basis. The higher this number, the stronger the results.

3. Test Conclusions

The report also shows one of two conclusions: “is not excluded as the biological father” or “is excluded as the biological father.”

• If the conclusion states, “is not excluded as the biological father,” this means the possible father most likely IS the biological father of the child, since all data gathered from the test supports a relationship of paternity.
• If the conclusion states, “is excluded as the biological father,” this means the possible father IS NOT the biological father of the child, since all data gathered from the test do not support a relationship of paternity.

Frequently Asked Questions

What percentage on a paternity test means you are the father?

On a DDC report, a Probability of Paternity of 99.99% or higher confirms that the tested man is the biological father. A result of 0% means he’s excluded and is not the biological father. There is no gray area in the final conclusion: your report will always read either “is not excluded as the biological father” or “is excluded as the biological father.”

My test shows a mismatch in one location between the possible father and the child, yet the probability of paternity is over 99%. How can this happen?

Chances are good that there was a mutation in either the child’s or the possible father’s genetic code at that location. Analysts take mutations into account when doing their calculations and reaching conclusions. So even if there is a mismatch, the man might still be considered the biological father of the child tested.

Can your paternity test results be wrong?

DDC processes every sample twice, by a separate team of technicians, to eliminate the possibility of human error for extremely accurate results. If your results say that the alleged father is “excluded”, this means there is zero probability that the person is the biological father, based on the DNA analysis. If your results say that the father is “not excluded”, this means that there is almost 100% probability that the person is the biological father – in the example above, a 99.9998% probability. However, if two possible fathers are close relatives, such as brothers, they share much of the same DNA. It is important to let us know if two possible fathers are relatives. We can do additional testing to increase accuracy in this situation.

Why aren’t there names on my paternity test report?

When doing an at-home test, there are no names on the report, only an identifying number for each set of samples and their role in the test (alleged father, child, or mother). We do this because we cannot verify whether a sample submitted to us belongs to the person indicated by the customer. However, if you choose to do a legal, witnessed, chain-of-custody paternity test with court-admissible results, then the report includes both names and our company branding. For both at-home and legal testing, the testing process itself is exactly the same, and you can be sure results are guaranteed accurate for the samples provided to us.

Can the Probability of Paternity ever be 100%?

No. DNA test results are calculated based on statistics. Quite simply, in order to get a 100% probability, we’d have to test every man in the world with a similar ethnic background to the alleged father being tested. And for obvious reasons, that’s not possible!

Does the mother need to be included to read the results?

No. DDC can determine paternity accurately with samples from just the child and the alleged father, so you may not see a mother’s column on your report at all. Including the mother’s DNA is optional, though it can strengthen the statistics in certain cases. Either way, your results are read the same way and are guaranteed accurate for the samples we receive.

About DNA Diagnostics Center (DDC)

DNA Diagnostic Center is the world leader in paternity and relationship testing. We serve healthcare professionals, government agencies, and individuals around the world to determine family relationships with trusted accuracy.

More Questions? Don’t hesitate to call us: we’re here to help!