You opened the envelope or the PDF, and now you are staring at a one or two-page document full of numbers, technical terms, and a verdict at the top. Most people focus on that verdict and skim the rest, but every line on a paternity test report is there for a reason. Knowing what each part means helps you understand how the lab reached its conclusion and whether the report you are holding is the right kind of document for your situation.
This guide walks through eight elements you will find on almost every paternity test report, one section at a time, in plain English. No prior lab knowledge required.
1. The Verdict Line: Inclusion vs. Exclusion
The verdict line is the sentence at the top of the report that states the conclusion. It usually reads something like "The alleged father cannot be excluded as the biological father" or "The alleged father is excluded as the biological father." These two phrases carry the entire weight of the test.
Inclusion means the tested man's DNA matches the child's DNA at every marker the lab examined in a way consistent with a biological father-child relationship. Labs do not usually write "he is the father" as a standalone statement. Instead, they say he "cannot be excluded" and pair that phrase with a Probability of Paternity figure that quantifies how confident they are.
Exclusion means the tested man's DNA is inconsistent with the child's DNA at multiple markers. In an exclusion, the Probability of Paternity is reported as 0%, and the Combined Paternity Index is reported as 0. A single mismatch does not always trigger an exclusion, because rare mutations can cause one marker to look inconsistent. Most labs require at least two or three clear mismatches before they call an exclusion, and they will state their threshold somewhere in the report.
Read this line carefully. The wording is precise on purpose, and a legitimate lab will not overstate the result in either direction.
2. Combined Paternity Index (CPI): What the Raw Number Means
Below the verdict, you will see a number called the Combined Paternity Index, or CPI. It might read something like 45,000 or 2,300,000. That number looks intimidating, but it has a simple meaning.
CPI is a likelihood ratio. It answers this question: how many times more likely is it that the tested man is the biological father than a random unrelated man from the same population? A CPI of 45,000 means the DNA evidence is 45,000 times more consistent with the tested man being the father than with a random man being the father.
The CPI is calculated by multiplying together the individual Paternity Index scores from every marker the lab tested. Each marker contributes its own small ratio, and those ratios are combined into the final CPI. A single marker rarely does the heavy lifting on its own. The strength of the result comes from testing many markers and multiplying their scores together.
Most legitimate labs report a CPI of at least 100 for an inclusion, and most reports come back well above 10,000. Court thresholds in many jurisdictions require a CPI of at least 100 before a paternity finding is accepted.
For a deeper walkthrough of how CPI is calculated and what different values mean, see our detailed article on the Combined Paternity Index and what the number on your report means.
3. Probability of Paternity: The Bayesian Percentage
Next to the CPI, you will see a percentage. It usually looks like 99.99% or 99.9999%. This is the Probability of Paternity, and it is derived from the CPI through a Bayesian calculation.
The formula treats the CPI as evidence and combines it with a prior probability, which is a starting assumption about paternity before the DNA evidence is considered. Most labs use a prior of 0.5, meaning that before the DNA is analyzed, the tested man is assumed to have a 50-50 chance of being the biological father. The CPI then shifts that starting point upward based on how strongly the DNA evidence supports paternity.
Here is where a lot of people get confused. The Probability of Paternity in an inclusion report never reaches exactly 100%. It might read 99.9999%, but it will not read 100%. This is a mathematical constraint, not a lab error. Because a random unrelated man could theoretically match by coincidence, the ratio never resolves to absolute certainty. The higher the CPI, the closer the percentage gets to 100 without ever touching it.
For more on why this ceiling exists and how to interpret different probability values, see why probability of paternity never reaches 100%.
4. The Marker Table: What "Matching Alleles" Means at Each Locus
The middle of the report is usually taken up by a table. Each row is a genetic marker, also called a locus, with a name like D3S1358, VWA, FGA, or TH01. Each row lists two numbers under the child's column, two numbers under the alleged father's column, and often two numbers under the mother's column if she was tested.
Those numbers are called alleles. Every person inherits one allele at each marker from their biological mother and one from their biological father. So if a child has alleles 14 and 17 at a given marker, one of those numbers came from the mother and one came from the father. If the mother was tested, the lab can identify which of the child's alleles came from her, and the remaining allele has to have come from the biological father. If the alleged father carries that allele, he is consistent with paternity at that marker.
If the mother was not tested, the lab compares the child's two alleles against the alleged father's two alleles and looks for at least one match. Every marker where a match exists contributes a Paternity Index score to the overall CPI.
USDC analyzes up to 28 genetic markers on each test, which is well above the industry-standard 20 or more markers used by most accredited labs. Testing more markers means a higher CPI and a tighter Probability of Paternity in an inclusion, and stronger confidence in an exclusion when mismatches appear.
The Short Tandem Repeat markers listed on your report are documented in the U.S. National Institute of Standards and Technology STRBase database, which is the reference resource for forensic DNA markers used worldwide.
5. The Chain-of-Custody Statement (or Absence of One): What It Signals
Court-admissible DNA reports include a chain-of-custody statement. It typically appears near the bottom of the report and describes how the samples were collected, who collected them, how they were shipped, and who received them at the lab. It confirms that the samples were handled by neutral third parties from collection through analysis, with signed documentation at every step.
If you are holding a report from an at-home paternity test, this section will not be present. Home paternity tests, including the one USDC offers, are self-collected. The people being tested swab their own cheeks, seal the swabs in the provided envelopes, and mail them to the lab. There is no neutral witness to confirm whose DNA is on the swabs. That is not a flaw in the test itself. The lab work is the same as a legal test. But the absence of a chain-of-custody statement means the report cannot be used in court, in a child support case, in an immigration proceeding, or on a birth certificate.
If your report has no chain-of-custody statement, it is a personal knowledge test only. That is exactly what most people need, and it is significantly less expensive than a legal test. But if the situation might involve a court or a government agency at any point, you will need a legal test collected under supervised chain-of-custody conditions.
For a full explanation of how chain-of-custody works and what makes a DNA test court-admissible, see our knowledge page on chain of custody in DNA testing and the detailed article on what makes a DNA test court-admissible.
6. Lab Accreditation Line: What to Look For
Somewhere on the report, usually in the footer or on a certification page, the lab will list its accreditations. This tells you which independent bodies have audited the lab and certified that it meets specific standards for testing accuracy, sample handling, and quality control.
The main accreditations you will see referenced in the DNA testing industry are:
- AABB (formerly the American Association of Blood Banks): The gold standard for relationship DNA testing in the United States. AABB accreditation is required for legal paternity tests used in court and for immigration DNA tests submitted to USCIS. AABB audits cover proficiency testing, personnel qualifications, sample chain-of-custody, and reporting standards.
- CAP (College of American Pathologists): A broader clinical lab accreditation that covers a wide range of laboratory disciplines, including molecular genetics.
- ISO/IEC 17025: An international standard for testing and calibration laboratories, often held by forensic labs.
- CLIA: The Clinical Laboratory Improvement Amendments certification, which is required for any lab that reports patient results in the United States.
Not every accreditation is relevant to every use case. If you plan to use the report in court or for immigration, AABB is the one that matters. For personal knowledge testing, CLIA certification of the underlying lab is sufficient. The AABB accreditation program page lists the specific standards audited for relationship testing labs.
If your report lists no accreditations at all, treat that as a red flag and ask the provider directly.
7. Report Date and Sample Receipt Date: What Timeline the Report Reflects
The report will show two dates. One is the date the samples were received at the lab. The other is the date the report was issued. These two dates matter more than most people realize.
The receipt date tells you when the lab took control of the samples and started the testing process. Turnaround times are measured from this date, not from the day you mailed the swabs. If you shipped your swabs on the 1st and the lab received them on the 4th, and your results were reported on the 6th, the lab processed your test in two business days.
The report date is when the final report was signed and released. If you need to submit the report to another party, they will look at the report date to confirm it reflects current information. Some agencies require reports to be dated within a certain window, often 90 days, of the submission date.
If the two dates are very far apart, that is worth asking about. Legitimate labs finalize reports within a few business days of sample receipt, not weeks. A long gap can indicate a re-run due to a sample problem, a contamination issue, or a scheduling delay in the lab.
For context on what can go wrong during processing and how labs catch it, see our article on DNA sample contamination and how labs detect it.
8. The Signature and Certification Line: Who Authenticated the Result
The final element on a paternity test report is the signature block. This is where a qualified individual at the lab, usually the laboratory director, a certifying scientist, or a forensic analyst, signs off on the report and takes responsibility for its accuracy. Their credentials, typically a Ph.D., M.D., or a board certification in molecular genetics or forensic biology, are printed next to their name.
This signature is not a formality. It means a specific qualified person reviewed the raw electropherogram data, confirmed the allele calls, checked the calculations, and vouches for the conclusion. In court settings, that person can be called to testify about the report. On personal knowledge reports, the signature confirms that the lab stands behind the finding.
Look for a real person's name, a real credential, and a date. Reports that lack a named signatory, or that list only "Lab Director" without a name, do not carry the same weight. The International Society for Forensic Genetics publishes recommendations from its DNA Commission on how relationship testing reports should be authored and signed, and reputable labs follow those recommendations.
Putting It All Together
Read from top to bottom: verdict, CPI, Probability of Paternity, marker table, chain-of-custody statement or absence thereof, lab accreditations, dates, and signature. Each element supports the others. The verdict is only as trustworthy as the CPI that backs it. The CPI is only as strong as the number of markers tested and the quality of the lab that ran the test. The lab's credibility rests on its accreditations and the person who signs the report.
If you are considering ordering a test and want to see what a report will look like before you commit, USDC's home paternity test kit includes a sample report format in the confirmation email so you know what to expect when your results arrive.
Common Report Questions
My report says 99.99% Probability of Paternity. Is that as good as 100%?
For practical purposes, yes. A 99.99% Probability of Paternity means the DNA evidence overwhelmingly supports the conclusion that the tested man is the biological father. The percentage never reaches exactly 100% because of how the Bayesian calculation works, but any Probability of Paternity above 99% is treated as a positive inclusion by labs and courts. Higher values, such as 99.9999%, simply reflect that even more markers matched, providing even stronger evidence.
Why does my report show 0% Probability of Paternity?
A 0% Probability of Paternity, paired with a CPI of 0, means the tested man is excluded as the biological father. This happens when there are multiple mismatches at genetic markers that cannot be explained by mutation. Most labs require at least two or three clear mismatches before they issue an exclusion, so a 0% result is a definitive scientific finding, not a marginal call.
Can I use my at-home paternity test report in court?
No. At-home paternity tests, including USDC's home test, are for personal knowledge only. Because the samples are self-collected without a neutral witness, the report does not include a chain-of-custody statement and cannot be admitted as evidence in court, used in child support proceedings, submitted for immigration cases, or used to change a birth certificate. If you need a court-admissible result, you will need a legal paternity test that uses supervised collection with documented chain-of-custody. USDC's legal paternity test kit is Coming Soon.
The tested man's alleles don't match at one marker. Does that mean exclusion?
Not necessarily. A single mismatch at one marker out of 20 or more can be caused by a rare mutation, which occurs at a low but predictable rate in human DNA. Labs are trained to distinguish between mutation and true exclusion. Most labs will only issue an exclusion when there are at least two or three clear mismatches across the markers tested. If your report shows one mismatch but still concludes inclusion, that means the lab evaluated the mismatch as a probable mutation and the rest of the marker profile strongly supports paternity.
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