TL;DR: DNA tests are highly accurate—paternity tests reach 99.9%+ accuracy, and forensic DNA tests are among the most reliable tools in science. But errors can and do happen. Lab contamination, poor sample collection, and human handling mistakes are the most common culprits. Choosing an accredited lab and following proper procedures dramatically reduces the risk.
So you’ve taken a DNA test—or you’re thinking about it—and now you’re wondering: can the results actually be wrong?
It’s a fair question. DNA testing carries enormous weight. Paternity results can reshape families. Ancestry results can change how people understand their heritage. And in criminal cases, forensic DNA evidence can determine whether someone goes free or goes to prison. The stakes don’t get much higher.
The short answer is yes, DNA tests can be wrong—but it’s rare when everything is done correctly. The science behind DNA testing is remarkably precise. The problems usually come down to human error, poor sample handling, or cutting corners on lab standards.
This article walks you through how accurate different types of DNA tests actually are, what causes errors when they do occur, and how to make sure your results are as reliable as possible.
How Accurate Are DNA Tests?
Before diving into what can go wrong, it helps to understand just how good DNA testing is under normal conditions.
Here’s a quick breakdown:
| DNA Test Type | Accuracy Level | Risk of Error |
|---|---|---|
| Paternity test | Very High (99.9%+) | Very Low |
| Sibling test | High | Low to Moderate |
| Ancestry test | High (estimates) | Moderate |
| Forensic test | Very High | Very Low (in controlled labs) |
Paternity DNA tests are the gold standard. When performed by an accredited lab using proper procedures, they achieve accuracy rates above 99.9%. Forensic DNA tests are similarly reliable—when handled correctly, they’re considered one of the most powerful forms of evidence in existence.
Ancestry DNA tests work differently. They don’t tell you with certainty that you’re 40% Irish—they estimate your ethnicity based on reference populations. That introduces a layer of interpretation, which means there’s more room for variation between different companies’ results.
Can a DNA Test Be Wrong?
Short Answer
Yes—but it’s very rare when the test is performed by an accredited laboratory following established procedures. The science itself is solid. Most errors trace back to something that happened before the sample even reached the lab.
What “Wrong” Actually Means in DNA Testing
“Wrong” can mean different things depending on the context.
It might mean a misinterpretation of results—where the data is read incorrectly, or the statistical output is misunderstood. It might mean lab contamination, where someone else’s DNA accidentally enters the sample. It could be a simple sample mix-up, where two people’s samples get switched. Or it might come down to statistical limitations, particularly in complex relationship tests like sibling or half-sibling comparisons.
Understanding which type of error is most relevant to your situation can help you ask the right questions if you ever doubt a result.
Types of DNA Test Errors
False Positive Results
A false positive means the test incorrectly shows a biological relationship that doesn’t actually exist. In paternity testing, this would mean the test concludes someone is the biological father when they’re not.
This is extremely rare in accredited labs. The probability calculations used in modern paternity testing are designed specifically to avoid this outcome.
False Negative Results
A false negative is the opposite—the test fails to detect a biological relationship that does exist. This is more likely to happen when sample quality is poor, DNA is degraded, or there isn’t enough genetic material to analyze properly.
Human Error in Sample Handling
This is one of the most common real-world causes of inaccurate DNA results. Mislabeling a sample, mixing up collection kits, or breaking the chain of custody (the documented process of handling a sample from collection to analysis) can all introduce errors that have nothing to do with the science.
Lab Contamination
Contamination happens when foreign DNA—from a lab technician, another sample, or the environment—enters the sample being tested. Reputable labs have strict protocols to prevent this, but it can still occur in poorly managed facilities.
How Paternity DNA Tests Can Be Wrong
Sample Collection Mistakes
Cheek swabs are the most common collection method for paternity tests. If the swab is contaminated—say, by touching it with bare hands or collecting the sample shortly after eating—it can compromise the DNA quality.
There’s also the issue of incorrect participant samples. If the wrong person submits a sample, the results will obviously be wrong—but through no fault of the lab.
Improper Chain of Custody for Legal Tests
Legal paternity tests (used in court cases) require strict identity verification. The sample collection must be witnessed, and the chain of custody must be documented every step of the way. If this process is skipped or done incorrectly, the results may be inadmissible—or worse, inaccurate.
Home paternity tests don’t carry the same legal requirements, which is why they can’t typically be used in court.
Rare Genetic Variations
In very rare cases, genetic mutations can affect how DNA markers are read. This might cause a test to appear inconclusive or, in unusual circumstances, return a result that doesn’t fully reflect the biological relationship. This isn’t common, but it’s a known limitation of the technology.
When Additional Testing Helps
Including the mother’s DNA in a paternity test improves accuracy. It helps the lab eliminate the mother’s genetic contribution, making it easier to isolate the father’s DNA markers. Testing additional relatives can also strengthen the analysis when a standard test returns an unclear result.
Can Ancestry DNA Tests Be Wrong?
Understanding Ethnicity Estimates
Ancestry DNA tests don’t directly read your family history. They compare your DNA against reference populations—large databases of people with documented ancestry from specific regions—and estimate where your DNA most closely aligns.
The keyword here is estimate. These aren’t exact measurements. Reference populations vary between companies, and they’re constantly being updated as databases grow.
Why Results Can Differ Between Companies
If you’ve tested with both 23andMe and AncestryDNA, you may have noticed the results don’t match perfectly. That’s not a sign that one is wrong. Each company uses a different reference database and a different algorithm to interpret the data.
Think of it like two different maps of the same territory—they both reflect reality, but they’re drawn differently.
Why Siblings Can Get Different Ancestry Results
This surprises a lot of people. Two full siblings can get noticeably different ethnicity estimates from the same company. Why?
Because each person inherits a random selection of their parents’ DNA. You don’t get exactly half from each parent—you get a unique combination. So two siblings might inherit different segments of their grandparents’ DNA, leading to slightly different ancestry breakdowns.
Neither result is wrong. They’re just different slices of the same genetic pie.
Can Forensic DNA Tests Be Wrong?
Crime Scene DNA Analysis
Forensic DNA testing is extraordinarily accurate under controlled conditions. When a clean sample is properly collected, preserved, and analyzed in an accredited lab, the likelihood of an error is extremely small.
The FBI’s Combined DNA Index System (CODIS) uses 20 genetic markers to identify individuals, making the odds of a random match astronomically low.
Risks in Forensic Settings
Crime scenes are not controlled lab environments. DNA evidence can be contaminated by first responders, investigators, or environmental conditions. Samples can also degrade over time, especially if exposed to heat, moisture, or sunlight.
A degraded or contaminated sample doesn’t always produce a false result—it might simply produce an inconclusive one. But in cases where a partial profile is used, the risk of misidentification rises.
The Importance of Proper Handling Procedures
Every step of the forensic process—from collection at the crime scene to analysis in the lab—needs to follow strict protocols. Errors introduced early in the process can’t always be corrected later. This is why chain of custody documentation is treated so seriously in legal proceedings.
What Causes DNA Test Errors?
Poor Sample Quality
DNA can degrade. Exposure to heat, moisture, bacteria, or UV light can break down the genetic material in a sample, making it difficult or impossible to get a clean reading.
Insufficient DNA quantity is another issue. If a swab doesn’t contain enough cellular material, the lab may not have enough DNA to analyze properly.
Human Handling Errors
Mislabeling samples is more common than you’d think. So are data entry mistakes when transcribing results. These errors aren’t caused by the science—they’re caused by people, and they can happen in even well-run labs.
Laboratory Issues
Contaminated equipment, poorly maintained machines, or outdated technology can all affect test accuracy. This is one of the main reasons why choosing an accredited lab matters so much.
Interpretation Errors
Some results require careful statistical interpretation. This is especially true in complex relationship tests—like half-sibling or grandparent tests—where the genetic overlap between individuals is less clear-cut. Overlapping genetic markers or unusual genetic profiles can sometimes lead to ambiguous results that are interpreted incorrectly.
How to Make Sure Your DNA Test Is Accurate
Choose an Accredited Lab
Look for labs certified by AABB (American Association of Blood Banks), ISO 17025, or CLIA (Clinical Laboratory Improvement Amendments). These certifications mean the lab has been independently audited for quality and accuracy.
If a lab can’t tell you about its accreditation, that’s a red flag.
Follow Sample Collection Instructions Carefully
Read the instructions that come with your kit. Don’t eat, drink, or smoke for at least 30 minutes before collecting a cheek swab. Don’t touch the swab tip. Store and return the sample exactly as directed.
Small mistakes during collection can affect the quality of your DNA sample more than most people realize.
Use Legal Chain-of-Custody Testing for Court Cases
If your paternity test results will be used in a legal dispute, don’t use a home kit. You need a legal test where sample collection is witnessed, and the chain of custody is fully documented. Results from home tests aren’t accepted in most courts.
Test Multiple Family Members When Possible
More data points mean more accurate results. If you’re testing for paternity, including the mother improves accuracy. For relationship tests involving distant relatives, testing multiple family members can help clarify ambiguous results.
Can You Challenge a DNA Test Result?
Requesting a Re-Test
Yes. If you doubt a result, most labs will allow you to submit a new sample for re-testing. This is especially worth doing if you suspect a collection error or contamination.
Using a Different Laboratory
You’re not bound to accept results from one lab. Getting a second opinion from a different accredited laboratory is a legitimate and common course of action—particularly in high-stakes situations like paternity disputes.
Legal Disputes and Expert Review
In legal cases, DNA evidence can be challenged in court. Both sides can bring in expert witnesses to examine the methodology, review the chain of custody, and evaluate whether proper procedures were followed. Courts generally give significant weight to DNA evidence, but it can be scrutinized and contested.
Common Myths About DNA Test Accuracy
Myth #1: DNA Tests Are Always 100% Accurate
No test is 100% accurate—DNA included. The science is extremely reliable, but errors can occur. Most come from human handling mistakes, not flaws in the technology itself.
Myth #2: Two Labs Will Always Give Identical Results
Not necessarily. Different labs use different markers, reference populations, and algorithms. Results should be consistent in most cases, but small differences—especially in ancestry estimates—are normal.
Myth #3: A DNA Test Can Be Easily Tampered With
Tampering is difficult and rare. Accredited labs follow strict protocols to verify sample integrity. Legal tests include identity verification and documented chain of custody specifically to prevent this.
Myth #4: Home DNA Kits Are Unreliable
Home DNA kits from reputable companies like AncestryDNA and 23andMe use the same core technology as professional labs. They’re reliable for ancestry and health-related insights. The main limitation is that they don’t follow a legal chain of custody, so they can’t be used in court.
Frequently Asked Questions
Can a DNA test be wrong?
Yes, but it’s rare when performed correctly by an accredited lab. Most errors stem from sample contamination, mislabeling, or poor handling—not the DNA analysis itself.
How often are DNA tests incorrect?
There’s no single published rate that applies across all DNA tests. Paternity tests from accredited labs achieve accuracy above 99.9%. Errors are most common in home-collected samples or tests processed by non-accredited facilities.
What can cause a false DNA test result?
The main causes include contaminated samples, insufficient DNA quantity, mislabeled samples, lab contamination, and interpretation errors in complex relationship tests.
Can a paternity test be wrong if the mother is not tested?
It can be slightly less precise, but modern paternity tests are designed to work without the mother’s sample. Including her DNA improves accuracy by helping eliminate shared genetic markers, but her absence doesn’t invalidate the test.
Can ancestry DNA results change over time?
Yes. Ancestry companies regularly update their reference populations and algorithms. This means your ethnicity estimates can shift slightly between updates—even without submitting a new sample.
Can a DNA test be challenged in court?
Yes. Legal DNA results can be challenged based on procedural errors, chain of custody issues, or improper lab standards. Both parties in a dispute can present expert witnesses to review the evidence.
Are home DNA tests as accurate as lab tests?
For ancestry and wellness testing, home kits from reputable companies are generally reliable. For legal matters—such as paternity disputes—a home kit isn’t sufficient. You’ll need a test conducted under a proper chain of custody.
Can a DNA Test Be Wrong?
DNA testing is one of the most accurate scientific tools available to us. When done correctly—by an accredited lab, with a quality sample, and proper handling procedures—the margin for error is extremely small.
But “done correctly” is doing a lot of work in that sentence.
The science rarely fails. People do. Mislabeled samples, contaminated swabs, broken chains of custody, and poor-quality collection methods are responsible for the vast majority of DNA testing errors. The technology isn’t the weak link—the human element is.
The practical takeaway? Always use an accredited lab. Follow collection instructions carefully. If the results will be used in a legal context, make sure you’re using a legal test with proper identity verification. And if you ever doubt a result, getting a second test from a different lab is always an option.
DNA tests aren’t perfect. But they’re about as close as we’ve got.
