Can paternity test DNA samples be contaminated?

Casey Randall Alphabiolabs

By Casey Randall, Head of Genetics at AlphaBiolabs
Last reviewed: 18/03/2024

In this article, we look at how DNA samples for paternity testing can become contaminated: and what you can do to ensure your DNA samples are suitable for testing.

What is a paternity test?

A paternity test is a type of DNA test used to determine the identity of a child’s biological father.

It is typically performed using cheek (buccal) swabs, which are used to collect cheek cell DNA from the alleged father(s) and the child.

These samples are then analysed and compared in the laboratory, to identify matching DNA markers (loci). If the tested man is the biological father, the man and the child will share DNA at every tested marker. If the tested man is not the biological father, this will not be the case.

Order a Paternity Test online

How are DNA samples collected?

A cheek (buccal) DNA sample is collected using cheek swabs, which are rubbed on the inside of the cheek to collect DNA.

For an AlphaBiolabs paternity DNA test, each sample donor must provide two cheek swab samples using the cheek swabs included in the test kit.

To collect the samples, the donor rubs one swab on the inside of the right cheek, and the other swab on the inside of the left cheek. The individual swabs must be rubbed on the inside of each cheek for at least 20 seconds to ensure enough DNA is collected for testing.

Each swab must then be placed into the sample envelope provided with the test kit, and the envelope sealed, ensuring the required information on the front of the envelope has been completed fully.

The cheek swab samples can then be posted to our laboratory for testing.

Related: Swabs vs. blood samples for DNA testing

Can paternity DNA test samples become contaminated?

With at-home DNA testing kits more affordable than ever, more and more people are now able to collect their own DNA samples for laboratory testing in the privacy of their own home.

This increase in at-home sample collection does mean, however, that DNA samples can sometimes become contaminated if they are not collected correctly before being sent to the laboratory.

AlphaBiolabs’ at-home DNA tests have been developed with the customer in mind, with straightforward instructions included in your test kit, that enable you to collect your own DNA samples quickly and easily.

However, there are a few ways that your DNA samples could become compromised if these instructions are not closely followed. Examples include:

Eating, drinking and/or smoking before collecting your samples

Paternity testing is performed using DNA samples collected via cheek (buccal) swabs.

Eating, drinking and/or smoking prior to collecting your samples can introduce other substances into the mouth that will be collected along with cheek cells.

These substances can compromise the quality of the DNA profile obtained via the swab, which can render the DNA sample unusable.

For this reason, it is important for each person taking part in the DNA test to avoid eating, drinking or smoking for at least 30 minutes prior to cheek samples being collected.


Cross-contamination can occur when:

Collecting DNA samples incorrectly from multiple individuals for the same test

For example, for a paternity DNA test, cheek swab DNA samples need to be collected from the child and the alleged father(s) for testing; samples should be collected one at a time to prevent cross-contamination.

If the child being tested is a baby that is being breastfed, sample collection should take place before feeding and not after, to avoid contamination with the mother’s DNA.

Cheek swabs come into contact with other surfaces

This can affect the quality of the DNA sample, rendering it unusable.

Failing to send your samples to the laboratory immediately following collection

DNA can degrade if left for a long time, which can impact our ability to obtain a usable profile from the cheek swab sample once it arrives at the laboratory.

Putting your swabs in a plastic bag or sandwich bag

Plastic stops the swabs from drying out, which can encourage microbial growth. Microorganisms can degrade the DNA, meaning we are less likely to obtain a result from your sample.

How to collect DNA samples properly

To ensure your samples are usable for testing, DNA samples must be collected properly, by following the instructions provided in your DNA testing kit.

Here are a few simple steps you can take to prevent your DNA samples becoming contaminated, and to ensure enough DNA is obtained for testing at our laboratory:

Collect your own samples

In cases where this is not possible, such as when collecting a child’s DNA sample, it is important to make sure you do not contaminate their sample with your own DNA by avoiding contact with the head of the swab, and ensuring swabs are placed into the envelope with both facing in the same direction.

Avoid eating or drinking before collecting your samples 

You should avoid eating or drinking at least 30 minutes before collecting your cheek swab DNA samples. This is because residual food on the swabs can cause mould or bacteria to grow.  This can interfere with the testing process, meaning that we are unable to generate a DNA profile.

Do not put your swab(s) in a plastic or sandwich bag

Plastic can stop the swabs from drying out, which can encourage microbial growth. This can degrade the DNA, making it less likely that the laboratory will be able to obtain a result from your sample.

Once you have collected your DNA samples, place the swabs into the paper sample envelope provided. The swabs must also be facing the same direction in the sample envelope.

Each person taking part in the test will have their own sample envelope for their swabs.

Do not collect your samples too early

Only collect your DNA samples if you are ready to send them back to the laboratory. DNA samples can start to degrade after a while, which may impact the ability of the laboratory to obtain a usable profile from your sample.

For the highest quality DNA profile, return your samples to the laboratory as soon as possible after collection.

Other steps you can take to protect your DNA samples for testing include:

  • washing your hands before you collect your samples
  • removing any lipstick or gloss before collecting your samples
  • only removing your swabs from the sterile packaging once you are ready to collect your samples
  • putting your swabs straight into the envelope after sample collection

Why is it important to use a reputable DNA testing laboratory?

If you are looking at options for DNA testing, it is important to consider all the factors that could impact your experience throughout the testing process, including the type of DNA test you need, and the credibility of the DNA testing company.

This is because DNA testing is often an extremely sensitive process, the results of which can have a significant impact on families. This makes the reliability and trustworthiness of the DNA laboratory crucial.

As a leading UK provider of DNA testing for members of the public, family law firms and social workers, we know that techniques, methodology and outstanding customer service play a key role in building customer confidence in a DNA testing laboratory. 

Here are a few more things to keep in mind when choosing a DNA testing provider:  


You can learn more about a company’s reputation by reading online reviews and testimonials from previous customers, which can provide valuable insight. However, you might also want to consider whether they have been recommended by other reputable partners and trusted sources.

Here are a few reasons why you can trust AlphaBiolabs with your DNA testing needs:

  • Government-accredited testing laboratory,accredited by the Ministry of Justice to carry out DNA relationship tests as directed by the civil courts in England and Wales under Section 21 of the Family Law Reform Act (1969).
  • Over 1 million genetic tests performed since the company was established in 2004
  • ‘Excellent’ rating on Trustpilot, based on real feedback from satisfied customers across the UK
  • All testing performed at our in-house laboratory, by highly-skilled and expertly trained DNA scientists, using the very latest scientific techniques and methodology
Related: How to choose the right DNA testing company

Testing accuracy and quality

A good indicator of DNA test accuracy includes everything from the accreditation and certifications held by thekl company to the laboratory processes and technology used to perform the test, and whether DNA samples are analysed in-house.

AlphaBiolabs holds UKAS ISO 17025 accreditation, as well as being certified to ISO 9001 – the internationally-recognised standard for the quality management of businesses, so you can be assured you will always get the best customer service from us.

The type of DNA test you need

It is important to check that the DNA testing company has the correct procedures in place for the type of DNA test that you require.

For example, an at-home DNA test enables you to collect your own sample at home. However, the results of these tests are for your own peace of mind and cannot be used for legal purposes.

If you need a DNA test for legal matters such as changing the name on a birth certificate, for child maintenance and custody disputes, or for wills and probate, the DNA testing company must have the correct procedures in place to ensure the DNA test results are legally admissible.

For an AlphaBiolabs legal DNA test, samples are collected under strict chain of custody procedures by a trained sample collector, ensuring DNA samples are collected from the right people, in the right way.

Our DNA test results are accepted by a variety of organisations for legal matters, including the Family Court, the Child Maintenance Service, the Home Office, and UK Visas and Immigration.

Find more about our legal DNA testing

It is also worth considering what the test can offer in terms of specific features, such as the number of DNA markers (loci) analysed.

AlphaBiolabs’ industry-leading DNA tests already analyse up to 25 DNA markers (loci) – way ahead of the industry standard of 16-21 markers.

What sets us apart is that we can also analyse up to 45 DNA markers, allowing for even more genetic material to be analysed, which strengthens the results of the test and provides additional reassurance.

This comprehensive analysis is especially useful when performing DNA paternity tests, where:

  • A close male relative may be the biological father of the child
  • The mother’s sample is not included or unavailable
  • Where you are looking for additional reassurance regarding the DNA test result

It is also helpful for more complex relationship tests, such as sibling, aunt, uncle, and grandparent tests, where the chance of obtaining a conclusive result is not as high as the more straightforward paternity or maternity tests.

Privacy and security

There are many reasons why privacy and confidentiality are of the utmost importance for peace of mind and legal DNA testing.

After all, many people who buy DNA tests online choose to do so without telling anyone about their decision to order a test. This means that discreet delivery of the DNA test kit – and the DNA test results – is essential.

Here’s how we ensure 100% privacy and confidentiality for all AlphaBiolabs’ customers:

  • We password protect all data – all our reports are sent as a PDF file, requiring a password to open them.
  • We never sell on your data – in fact, we limit access to your personal data to only those individuals who have a business need to know
  • We keep your results and personal information secure – we also use a secure server that protects any financial transactions on our website
  • We adhere to the General Data Protection Regulation (GDPR) – this means that all DNA samples and all identification documents are destroyed in accordance with this regulation

Level of customer support available

It is important to choose a DNA testing company that can offer the right level of customer support before purchasing your test, right through to the delivery of your test results in a secure, confidential way.

You can gain insight into the customer support available by looking at customer reviews – such as those posted via Trustpilot or Google – and by checking that the company is contactable, with phone numbers and email addresses that are easy to find, should you need assistance.

Speed of the DNA test results

For most people ordering a DNA test, it is important that the results come back quickly, to reduce any stress or anxiety that may be felt while waiting for the results.

This is especially true in situations where the result of the test could have a significant impact on family relationships.

If you need the results of your test quickly, be sure to choose a company that can offer rapid results.

At AlphaBiolabs, for example, we pride ourselves on offering 100% accurate, reliable results quicker than any other UK laboratory.

Depending on which DNA test you choose, you could receive your results the next day* – or even the same day*, for an additional fee.

*From receipt of your samples at our laboratory.

The cost of the DNA test

Consider what is included in the cost of the DNA test. For example, does the test include all fees for laboratory testing and analysis, or just the price of the test kit?

Is the price reasonable when compared to other testing companies offering equivalent tests of the same quality?

At AlphaBiolabs, we pride ourselves on offering high quality DNA testing with rapid results, at a highly competitive price.

For most of our DNA tests the price of the test includes your testing kit, FREE shipping for your testing kit, and all fees for laboratory testing and analysis.


What can you find out about the company’s services before purchasing your DNA test?

For example, do they provide enough detail about their testing methodology, pricing, and results via their website, or will you need to contact them for this information?

The more you can find out online before ordering your DNA test, the more confidence you will have when making your decision.

At AlphaBiolabs, we understand the sensitivity involved in purchasing a DNA test, which is why we offer a wealth of information on our website to help you make an informed decision about which test is best for you.

You can also find a wide variety of articles on DNA testing in our Learning Centre, covering everything from the types of DNA tests we offer, to how the tests are performed, and why you might need to order a DNA test.

Where can I buy a paternity test?

You can order your test paternity test online now, direct from our state-of-the-art, UKAS-accredited laboratory.

We offer two types of paternity test, depending on your needs:

  • Paternity Test: used to determine the identity of a child’s father using cheek swab DNA samples from the alleged father(s) and the child, and
  • Prenatal Paternity Test: which can be performed as early as 7 weeks into pregnancy, to determine paternity before a baby is born. For our Prenatal Paternity Test, a blood sample is required from the mother, along with cheek swab DNA samples from the mother and alleged father(s).

For more information or advice on which test is best for you, call our friendly and discreet Customer Services team on 0333 600 1300 or email

Home Paternity Testing Kits

Order your Paternity Test online now for just £99.

Casey Randall, AlphaBiolabs

Casey Randall

Head of Genetics at AlphaBiolabs

Casey joined the AlphaBiolabs team in 2012 and heads up both the DNA and Health testing teams.

An expert in DNA analysis and a member of the International Society for Forensic Genetics (ISFG), Casey holds an MSc with Distinction in DNA Profiling and a First-Class BSc with Honours in Forensic Science.

Casey is responsible for maintaining the highest quality testing standards, as well as looking for ways to further enhance the service that AlphaBiolabs provides and exploring new and innovative techniques in DNA analysis.

Related articles…

How accurate are Paternity tests?

Paternity testing is a highly accurate method of identifying whether a man is a child’s biological father. We look at what can affect test accuracy and how you can be sure that your results are correct.

Read more

Can you test Paternity when the possible fathers are related?

In this article, we look at how paternity testing is done when two or more potential fathers are related to each other.

Read more

Can you do a paternity test with hair?

We discuss paternity testing with hair, whether it is possible to establish paternity using a hair sample, and why cheek swabs remain the industry standard for at-home DNA testing.

Read more