Understanding Paternity Test Results

A Complete Overview to Understand Paternity Test Results 

AttoLife has provided thousands of Ministry of Justice-approved legal DNA test results for court cases under Section 20 of the Family Law Reform Act 1969, with analysis carried out in a UKAS-accredited ISO/IEC 17025 laboratory. We also have extensive experience providing peace of mind DNA testing outside the courtroom for individuals seeking confirmation of biological family connections.

At AttoLife, we understand that paternity DNA testing can be a stressful and emotional process, and interpreting paternity test results is not always straightforward.

Below, we’ve put together a complete guide to help solicitors and clients involved in paternity testing understand what the results mean and what steps to take next.

How Does Paternity Testing Work?

Paternity testing is now highly advanced, reliable, and widely used in the UK. At AttoLife, paternity DNA testing is commonly requested for legal matters such as:

• Child custody disputes
• Immigration cases
• Inheritance claims

Throughout the process, AttoLife prioritises confidentiality, privacy, and careful handling of all samples and data. 

Court-Requested Legal Paternity Testing

If an ongoing legal case requires a paternity DNA test, one of our professionally trained sample collection specialists will meet with your client at a pre-arranged location to collect a pain-free buccal (cheek) swab.

Unlike an at-home peace of mind test, your client cannot take the sample themselves. Professional sample collection ensures compliance with strict chain-of-custody requirements, so every swab is handled correctly, documented appropriately, and remains legally defensible.

Once collected, the DNA samples are sent to our UKAS-accredited ISO/IEC 17025 laboratory for analysis by an expert genetic analyst. The laboratory will examine  up to 50 short tandem repeat (STR) markers, which will either:

• Confirm paternity with a probability of 99.99% or higher, or
• Exclude paternity, where there is insufficient genetic match between the child and alleged father

This is what makes a legal paternity test suitable for court use and official purposes.

 

Peace of Mind Paternity Testing (At-Home Kits)

With a peace of mind paternity test, your client can order an at-home DNA test kit and collect the sample themselves. Professional chain-of-custody is not required for this option, but accuracy still depends on following the kit instructions carefully. The process is simple and painless, requiring a cheek swab.

Once your client returns the sample to our laboratories, the same core analysis methods are used to determine whether the tested individual is the biological father, with very high accuracy. Peace of mind testing can be ideal where the results are required for personal reassurance rather than court proceedings.

 

The Role of STR DNA Markers in Paternity Testing

STR DNA markers are highly variable regions of DNA used to compare a child’s DNA profile with the alleged father’s profile to determine the probability of a biological relationship.

These markers are located at specific points on the chromosomes and consist of short repeated DNA sequences. Every person has two copies of each STR marker (called alleles)—one inherited from the mother and one from the father.

At AttoLife, the laboratory analyses up to 50 highly informative STR markers, comparing the alleles between the child and the alleged father. Where the profiles match sufficiently across these markers, it is scientifically possible to report:

• A confirmed biological paternal relationship (typically 99.99%+), or
• An exclusion, where the alleged father is not the biological father

STR testing is the established gold standard for routine paternity testing, especially where only the child and alleged father are being tested.

 

AttoLife’s Advanced SNP Testing for Complex or Extended Relationships

AttoLife is one of the only providers in the UK offering advanced single nucleotide polymorphism (SNP) testing as part of a Ministry of Justice-approved service.

This is not usually required for standard paternity testing. However, SNP testing can be extremely valuable in cases involving more complex family relationships or where additional genetic resolution is needed.

These scenarios can include:

• Grandparent testing
• Aunt/uncle testing
• Cousin testing
• Other 2nd–4th degree relationship testing

In these cases, AttoLife can use an advanced analysis of 600+ SNP markers, which is designed to improve confidence in relationship testing where STR-based approaches may not be sufficient on their own.

 

Why the Combined Paternity Index (CPI) Matters

The Combined Paternity Index (CPI) is a statistical measure used to support paternity testing conclusions.

It works by comparing the alleged father’s DNA profile against how likely it would be to observe the same match pattern in an unrelated individual from the same ethnic background.

In simple terms, the CPI strengthens the statistical foundation of the report and helps explain why a 99.99%+ confirmation is overwhelmingly more likely than a random match.

Not all testing providers highlight the CPI clearly, but it is one of the core statistical concepts your client may encounter when researching how paternity results are calculated.

 

Understanding Paternity Test Results

When your client undertakes a paternity DNA test, the results are reported clearly, discreetly, and in a format aligned with the purpose of the test.

Legal Paternity Test Results (Court Use)

For a legal paternity test, the results will be issued in a formal report that states the outcome in court-appropriate language.

The report will typically confirm either:

• Paternity confirmed (usually 99.99%+ probability), or
• Paternity excluded (the tested individual is not the biological father)

Peace of Mind Paternity Test Results (Personal Use)

For peace of mind testing, the report is provided securely—usually via a protected online portal or secure link—so your client can access the results privately.

 

What to Do if the Paternity DNA Result Is Negative or Inconclusive

In most cases, paternity testing produces a clear result, either confirming or excluding paternity.

However, in rare situations, the results may be reported as inconclusive. This can happen due to factors such as:

• Sample quality issues
• The need for additional markers to strengthen statistical confidence
• Complex family structures or missing participant testing scenarios

At AttoLife, we recognise how emotionally difficult uncertain outcomes can feel. If your client’s results are inconclusive, AttoLife can provide additional testing using an extended marker set to help reach a clearer conclusion where possible.

In particularly complex cases, AttoLife can also offer advanced 600+ SNP marker analysis. While this is rarely needed for straightforward paternity cases, it can be highly valuable where extended relationship testing is required or where further confirmation is appropriate.

If your client is unsure what the results mean or what to do next, our team can guide your client through the available options with clarity, discretion, and care.

 

How Accurate Is Paternity DNA Testing?

Paternity DNA testing is highly accurate. At AttoLife, provided the sample collection procedure is followed correctly, the laboratory can confirm a biological paternal relationship with an accuracy of 99.99% or higher.

False positives are extremely rare when proper procedures are followed, particularly in legal paternity testing where chain-of-custody controls reduce the risk of errors, tampering, or mix-ups.

Where issues occur, they are more commonly linked to practical factors such as:

• Sample fraud
• Sample tampering
• Sample contamination
• Incorrect storage or transport
• Incorrect sampling or labelling

At AttoLife, rigorous processes are in place to reduce these risks and protect the integrity of the results.

 

Can Your Client Do a Paternity Test While Pregnant?

Search volumes show that many people ask whether a paternity test while pregnant is possible, including queries such as:

• “can you do a paternity test while pregnant”
• “can you get a paternity test while pregnant”
• “paternity test during pregnancy”
• “prenatal paternity test”

The short answer is: a prenatal paternity test may be possible, but the options depend on gestational stage and clinical suitability. Prenatal testing is different from post-birth testing, which typically uses cheek swabs from the child and alleged father.

If your client is considering a paternity test during pregnancy, AttoLife can explain the available pathways, what is involved, and whether post-birth testing may be the most appropriate option depending on the circumstances.

 

How to Tell Who the Father Is Without a Paternity Test While Pregnant

It’s common for clients to ask how to tell who the father is without a paternity test while pregnant, particularly where conception dates overlap or there is uncertainty.

However, from a scientific and legal perspective, there is no reliable way to confirm paternity without DNA testing. Timing, symptoms, and estimated conception windows cannot provide certainty, and they would not be acceptable evidence in a legal setting.

A DNA-based paternity test remains the only dependable method to confirm whether the tested individual is the biological father.

 

DNA Test Paternity UK: Next Steps

If your client needs a DNA test paternity UK service for legal proceedings, AttoLife can support the process from start to finish, including:

• Identity-verified sample collection
• Chain-of-custody documentation
• UKAS-accredited ISO/IEC 17025 laboratory analysis
• Clear reporting suitable for court use

If your client requires peace of mind testing, AttoLife can also provide at-home kits and secure reporting.

To discuss the most appropriate option, your client can contact our team on +44 020 3551 1493 or email info@AttoLife.co.uk.

 

Paternity Test Results: FAQs

Can your client do a paternity test while pregnant?

A prenatal paternity test may be possible, but the best option depends on gestational stage and clinical suitability. AttoLife can advise on the appropriate pathway and what the results can confirm.

Can your client get a paternity test during pregnancy in the UK?

Yes — paternity testing during pregnancy can be available in the UK, but it differs from post-birth testing and may involve additional considerations. Where appropriate, AttoLife will guide your client through the options.

How accurate are paternity test results?

Paternity testing is highly accurate. For standard paternity cases, the report will usually confirm paternity with 99.99%+ probability, or provide a clear exclusion where there is insufficient DNA match.

What does a 99.99% paternity result mean?

A 99.99%+ result means the DNA evidence strongly supports that the tested individual is the biological father, based on the markers analysed and the statistical calculation used in the report.

What does a 0% paternity result mean?

A 0% result (or “excluded”) means the tested individual is not the biological father, based on DNA mismatches across the markers analysed.

What happens if the paternity test results are inconclusive?

Inconclusive results are uncommon, but can occur due to  case-specific genetic factors. AttoLife can recommend additional testing to help clarify the results and strengthen confidence where needed.

What is a legal paternity test?

A legal paternity test is designed for court and official purposes. It includes identity verification, documented chain-of-custody, and analysis performed in a UKAS-accredited ISO/IEC 17025 laboratory, with results presented in a legally defensible report format.

How quickly will your client receive the results?

The majority of cases will be reported within one working day. Turnaround times for complex relationships vary depending on test type and case requirements. AttoLife will confirm expected timelines at the point of booking and keep your client informed throughout.

Get a Quote