Avoiding Erroneous Results - PTC Laboratories (2024)

How to avoiderroneous results.

Not all Paternity Testing is the Same

Most people assume that all DNA paternity tests are the same, and it doesn’t matter where you get your DNA test done. That could not be farther from the truth.

Even if you are using an accredited DNA paternity testing laboratory, the minimum required levels of paternity testing are very low. DNA paternity testing laboratories know that if they only test DNA to the minimum required level, a number of paternity test results every year will identify someone as the biological father when he is not (a “false inclusion”) or say that he is not the biological father when he actually is (a “false exclusion”).

The DNA paternity testing industry is regulated by the American Association of Blood Banks (AABB). The two committees at the AABB that actually establish the requirements for DNA paternity testing are composed of volunteers from private DNA paternity testing laboratories like PTC Laboratories. Historically, those committees have made certain that DNA paternity testing laboratories are following correct scientific procedure, but they have been less concerned about the amount of paternity testing that DNA paternity testing laboratories perform. The theory is that if a client wants additional DNA testing, the client can negotiate with the paternity testing laboratory to pay for additional DNA testing. The problem is that clients have no way to know if they need more DNA testing.

So PTC Laboratories provides the extra DNA testing automatically, at no extra charge. We are simply unwilling to release a DNA paternity test that we believe has any realistic chance of being incorrect. It is surprising that many DNA paternity testing laboratories do not feel that way. A Miami paper wrote a very interesting story that interviewed several DNA testing laboratories and demonstrates the wide variety of opinions regarding additional DNA testing.

Clients who have received DNA paternity tests from other DNA paternity testing laboratories, but question the results, sometimes send them to PTC Laboratories for review. We have received many such DNA paternity tests. The vast majority of those DNA tests have correctly identified the tested man as the biological father or not. But some of those DNA paternity tests have reached an incorrect conclusion. In those cases, if the client asks PTC Laboratories to perform the DNA paternity test on the same parties, we have been able to obtain the correct DNA paternity test result, explain to the client the reason that the other DNA testing laboratory obtained a wrong answer and are usually able to get the other DNA testing laboratory to correct their error and issue a corrected DNA paternity test report.

The problem is that in some of the cases of incorrect DNA paternity test results, the clients do not realize that their original DNA paternity test was wrong. Many live out the rest of their lives assuming that the DNA paternity test has provided a correct answer.

Some of the things that cause incorrect DNA paternity tests are discussed below.

False Inclusions of a DNA paternity test

A DNA paternity test works by identifying certain specific size pieces of DNA that the child received from the child’s biological father. If the DNA tested man has those same size pieces, then he could be the child’s biological father. But other men in the population will also have those same size pieces. So a DNA paternity testing laboratory tests additional DNA locations (genetic markers). In general, the more DNA locations that are tested, the more rare the total pattern will be. In other words, fewer other men will also have this pattern. The more rare the pattern is, the more likely it will be that the DNA tested man is truly the child’s biological father.

However, if DNA testing is stopped after identifying only a pattern that is somewhat common, then there is a greater chance that the DNA tested man is not the biological father, but is just one of the people in the population with this same somewhat common pattern. Thus, sometimes DNA paternity tests are incorrect because they have falsely included the DNA tested man as the biological father, when he is not. Those tests are not “technically incorrect,” as the laboratories issuing them will tell you, because the result just states a probability that the tested man is the biological father, and not a certainty. But the test has identified the wrong man as dad, and the DNA tested parties would therefore consider the test result to be incorrect. At PTC Laboratories we certainly agree.

Those DNA paternity testing laboratories that are more conscientious insist on continuing DNA testing until they achieve a pattern that is more rare than the required minimum level, and therefore provide a more reliable DNA paternity test. The industry only requires DNA testing until a 99% probability of paternity is achieved. But at that level of DNA testing, the identified DNA pattern would be possessed, on average, by one in every 100 men, and in some cases will be even much more common than that. At that level, there are still many men who would fit that pattern and who the DNA test would show to be the child’s biological father. Some DNA paternity testing laboratories insist on DNA testing until they achieve at least a 99.9% probability of paternity, which is a pattern that on average fits one in every 1,000 men. PTC Laboratories insists on testing until we achieve at least a 99.99% probability of paternity, which is a pattern that on average fits only one in every 10,000 men.

False Exclusions

DNA Paternity tests can falsely exclude someone who is truly the child’s biological father for a variety of reasons.

One major reason is simple human error. For example, it is possible at the time of the DNA specimen collection for the collector to accidentally place the child’s DNA specimen in the mother’s DNA specimen envelope and the mother’s DNA specimen in the DNA child’s envelope. This type of sample switch causes the DNA paternity testing laboratory to compare the alleged father’s DNA to the mother’s DNA, instead of to the child’s DNA. This has caused paternity testing laboratories to issue a paternity report that excludes the alleged father even though he is the biological father, because the samples were switched. PTC Laboratories puts a simple check in place which requires that for every test that appears to be an exclusion, we compare the alleged father’s DNA to the mother’s DNA, and if they match at all DNA locations, then we look into it further and correct any sample switch before we complete the DNA paternity test.

Another type of human error that has caused erroneous test results is the situation where the alleged father sent in an imposter (someone pretending to be the alleged father to provide a DNA sample). Sometimes this can go undetected if the mother is not able to identify the picture of the alleged father or was not present at the collection, but when it is detected, the alleged father is forced to go in himself and give a DNA sample. Sometimes the DNA paternity testing laboratory has accidentally reused the original sample and DNA tested the leftover portion of it instead of the new sample (because the original DNA sample still had the name of the alleged father on it).

False exclusions can also result from an inadequate amount of DNA testing. One way this occurs is by assuming that the DNA tested man is not the father just because his DNA fails to match the child’s DNA at two DNA locations. Quite often the child’s DNA mutates, so that the child’s DNA and father’s DNA do not match at one or a few DNA locations, even though the man really is the child’s biological father. Occasionally there can be two DNA locations where the child and biological father do not match, and extremely rarely the biological father can fail to match the child at three locations. The AABB’s minimum testing requirement is that the laboratory has to find at least two locations where they do not match, in order to issue a report excluding the alleged father. The theory is that mutations are pretty rare, so if there are two DNA locations that don’t match, then probably they are not mutations.

But DNA paternity testing laboratories realize that sometimes the two non-matching locations will both be mutations, and the man will actually be the biological father. PTC Laboratories tracks these events. In our experience, over half the time that the tested man and child fail to match at only two locations out of fifteen, additional testing proves that the man is actually the biological father. As a result, at PTC Laboratories we require stronger DNA testing. PTC Laboratories’ laboratory policy is to continue DNA testing until we either prove that the tested man is the biological father, or find at least four DNA locations where the man and child do not match. Some laboratories simply issue a DNA paternity test excluding the tested man after finding two non-matching locations, even though they are aware that a reasonable amount of additional testing could change the outcome of the DNA paternity test.

One example of this problem occurred a few years ago, when PTC Laboratories received an angry call from the Miami Family Court. The man in this case wanted to establish that he was the child’s biological father, and the man wanted to be involved in the child’s life. PTC Laboratories had shown that the man was the father. The judge wanted to know how two different DNA paternity testing laboratories could have issued DNA paternity tests with two different results for the same family. The answer was that the other laboratory had issued a test excluding the alleged father after finding only two locations where the man and child did not match. When this discrepancy was brought to the other DNA Paternity testing laboratory’s attention, they performed additional DNA testing and issued a new laboratory report agreeing that the man was the child’s biological father. A Miami paper (Miami Daily Business Review © August 11, 2003) wrote a very interesting story about this case.

DNA paternity testing laboratories performing only the minimum required amount of DNA testing know that they will sometimes be issuing incorrect paternity tests. At PTC Laboratories we implement additional DNA testing requirements and procedures to try to make sure that this does not happen to you.

Avoiding Erroneous Results - PTC Laboratories (2024)


What can throw off a DNA swab test? ›

Eating or drinking less than an hour before a cheek swab can also affect the outcome. Food or drink won't change the DNA but can mask them. Don't eat or drink for at least an hour before doing a cheek swab, and of course, carefully read any directions enclosed.

What are the odds of a DNA test being wrong? ›

Tests that test the DNA shared between a child and a parent can have a low chance of offering a false positive or come back inconclusive. However, when it comes to the modern DNA testing process, the chance of something being wrong or misleadingly inaccurate is less than a 10% chance.

How to make a DNA test inconclusive? ›

Inconclusive results also can occur if the evidentiary sample contains a mixture of DNA from several individuals (for example, a sample taken from a victim of a gang rape).

Can a DNA test be manipulated? ›

Fraud and Tamper

A mother may submit a sample of the man's other child to force a positive paternity test. Someone in the lab may tamper with the DNA samples or the test results to provide false results. In paternity lawsuits, parents may go to extremes to obtain the results that they desire.

Can mouthwash mess up a DNA swab test? ›

When submitting a replacement sample, we recommend reviewing the tips on providing a good sample, including: Do not eat, drink, smoke, chew gum, brush your teeth, or use mouthwash for at least 30 minutes prior to providing your sample.

Can eating affect DNA swab? ›

Food consumption does not affect your DNA, but could contaminate the buccal swab used for DNA sample collection. Food residue left in the mouth may contaminate the swab and inhibit the extraction of DNA from the swab. If you have eaten recently, the collection technician will ask you to rinse out your mouth.

How accurate are mouth swab paternity tests? ›

A DNA paternity test is nearly 100% accurate at determining whether a man is another person's biological father. DNA tests can use cheek swabs or blood tests. You must have the test done in a medical setting if you need results for legal reasons. Prenatal paternity tests can determine fatherhood during pregnancy.

What percentage of DNA gives false results? ›

This study focused on variants reported in the raw data of DTC genetic testing and our two key findings were an alarmingly high false-positive rate (40%) and the incidence of discrepant classification/misinterpretation of variants coming from DTC companies and/or third-party interpretation services.

How often is DNA evidence wrong? ›

Studies have shown that DNA evidence is 99% accurate, making it one of the most foolproof pieces of evidence you can possibly use in court. Like fingerprints, no two people have the same DNA. If a mistake occurs, it's typically because of human error.

What does 97% mean on a paternity test? ›

In many states, a person is legally presumed to be a child's father if his DNA test results indicate a certain minimum percentage of probability (typically 97% to 99%) that he's the biological father. If the mother or alleged father objects to the test results, they may request additional DNA tests.

How do you give a false DNA test? ›

Some examples of how DNA test results can be faked include via the substitution of the DNA of the individual being tested with someone else's DNA and the purposeful contamination of the DNA specimen or testing kit.

What does a inconclusive DNA test look like? ›

“Inconclusive” means that the test did not give clear results. An inconclusive result cannot confirm or rule out a diagnosis. Everyone has differences, or variations, in the way their genes appear. These variations are called polymorphisms.

Can DNA results be altered? ›

Tests Can Be Tampered With

Though uncommon, DNA fraud can affect the outcome of paternity testing, and there are several things you should be aware of if you are dealing with a paternity dispute. The most common way that DNA fraud may be executed is through test tampering.

Can a LabCorp DNA test be wrong? ›

Labcorp has been a leader in the genetic testing field for more than 30 years. Our results come with the guarantee of quality and are delivered with speed, convenience and most importantly, accuracy. Our results routinely provide a probability of paternity of either 99.99% or 0%.

Can DNA evidence ever be wrong? ›

According to the National Registry of Exonerations, 575 wrongly convicted people have been exonerated based on DNA tests that demonstrated their innocence since 1989.

How reliable are DNA tests? ›

Accuracy of the Reading of the DNA

Accuracy is very high when it comes to reading each of the hundreds of thousands of positions (or markers) in your DNA. With current technology, AncestryDNA ® has, on average, an accuracy rate of over 99 percent for each marker tested.

Can DNA matching be wrong? ›

“We're talking about 99.9 percent accuracy for these arrays,” Erlich says. But even with that high level of accuracy, when you process 1 million places in the genome, you might get 1,000 errors. Those small errors alone can help explain why one twin might have slightly different results from another.

Can DNA ancestry results be wrong? ›

Though it's possible that it's a mistake, it's extremely unlikely. Relationship predictions are almost always accurate for people who are second cousins or closer.


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