Is DNA Testing Accurate: The Deep Analysis into DNA Testing Stats

article by Joe Henneman
February 24, 2019
Is DNA testing accurate? Probably this thought has gone through the mind of many potential DNA testing kit buyers. All the DNA testing companies bragging about their advanced analysis technics and huge sample databases, but is it indeed as stated? or just an empty selling points. We looked deeply and this is what we found out.

In DNA We Trust?

DNA Test Kits are Wildly Popular — But are they Accurate?

“Fast is fine, but accuracy is everything.” -Wyatt Earp

Wyatt Earp, the gun-slinging lawman of the 19th century American West, knew a few things about precision. He helped take down the outlaw Clanton Gang in the famous 1881 Shootout at the O.K. Corral in Tombstone, Arizona. Bullets flew like a swarm of hornets, but Earp wasn’t injured. The outlaws didn’t fare so well. Three of the four were pushing up daisies by the time the legendary gunfight was over.

Earp knew nothing about DNA test kits, genealogy or genomics, but his Wild West lesson is well-taken. You can be many things, but nothing beats being accurate.

The importance of accuracy in home DNA tests has come more into focus as sales of the direct-to-consumer test kits have soared past 15 million. Send a cheek swab or vial of saliva off to the laboratory and science opens up a whole frontier of information. Millions learn where their ancestors might have come from and how their genes could affect their health, while adoptees find birth parents and others discover family members they never knew existed. Such a wealth of information at our fingertips, but how do we know it’s true? If a DNA report says you are 49 percent Irish or 22 percent African, can you believe it?

Test failures are hardly a daily occurrence, but there have been some well-publicized problems. The New York Times Magazine recently profiled a woman who always thought she was black but got a DNA test result that claimed she was not. After switching test vendors and doing more tests, the woman got contradictory results. Eventually a 23andMe test reported her heritage as nearly 50 percent African. In another case, the DNA testing vendor processed a sample without realizing it came from a dog.

On top of potential error, consumers face unexpected shock when DNA tests reveal a parent isn’t their biological mother or father, they have half-siblings across the country, or their heritage does not match any of the family stories from long ago. Such jolting results can lead customers to question the validity of tests, even when the tests are correct. Ancestry-related DNA tests get at a crucial, personal question: who am I? Trauma can result when the test data come as a great surprise. The stakes are high.

The science behind extraction and analysis of DNA is complex. Thankfully, there are ways to judge the accuracy and reliability of home DNA tests without earning a Ph.D. in molecular biology or genetics. But even with your due diligence, don’t hang your cowboy hat on hopes of finding a guarantee that you are 34.6 percent Italian or 7 percent Swedish, or that you might develop a dread disease one day. No matter what you are told, remember that much of the data included in DNA reports are estimates, not figures etched in granite. What one test kit tells you today could be drastically different in 18 months. It’s still a little like Wyatt Earp’s Wild West, just without the bullets. Or, as one genealogist blogger put it, “It’s not soup yet.”

A Map of Building Blocks

So what’s all the fuss about DNA? For hundreds of generations, it sat there inside virtually every human cell, quietly doing its job. Now it’s the talk of the town. Your DNA is the genetic blueprint that determines how your body grows, functions and reproduces. It is the main component in the 23 pairs of chromosomes you inherit from your parents. Your DNA consists of chemical sequences that are packed into the shape of a double-helix, which resembles a winding staircase. Most DNA is identical between humans, but a small percent contains differences or variants. Analyzing those variants can provide insight into ethnic heritage, physical traits —and risk of disease.

Before we take a look at the reliability of home DNA tests, let’s set the table just a bit. Just what kinds of tests are consumers buying for in-home use? What do brands like MyHeritage, Ancestry DNA, 23andMe, and Futura Genetics offer their customers?

  • Ancestry — Also known as heritage or family history tests, these kits gauge where your ancestors lived going back 6-7 generations. Within this category, there are three types of tests: autosomal (DNA from both parents), mitochondrial or mtDNA, which examines the lineage that mothers pass down through generations, and yDNA, the genetic material passed from fathers to sons. In addition to reporting a person’s regional ancestry makeup, deep ancestry tests promise to report on ancestors up to 100,000 years ago.
  • Health — These health DNA test kits look at variants in your DNA that could indicate an increased risk of developing various diseases. They also map out physical traits such as hair color and can indicate if you are a carrier of genes tied to diseases such as sickle cell anemia.
  • Lifestyle — A wide range of information is promised with lifestyle DNA tests, from whether you are likely to go bald if you could be prone to memory issues, or analysis of how DNA affects your skin care.
  • Paternity — Who’s the baby daddy? While parental issues are often settled in a court of law, home tests can put minds at ease if paternity is in doubt.
  • Dog Breeds — Is your favorite pooch an Australian Kelpie, an Appenzeller Sennehund, a Puggle or a mix of breeds? Dog DNA tests will analyze your pet’s DNA for markers associated with various breeds.
  • Others — There are a number of other consumer-type DNA tests on the market, although some are not for in-home use. These include funeral home DNA collection kits (for when family members forget to get a DNA sample from mum or grandma while they were alive); forensic kits that could identify DNA from the back of an old postage stamp; and even “infidelity tests” that analyze biologics from bedding or other material to determine if a spouse or partner is cheating.

What Do We Mean by ‘Accurate?’

It’s important to define and understand the terms if we’re to assess the validity of home DNA tests. What makes something accurate? The Merriam-Webster dictionary says something is accurate if it is 1) free from error, 2) conforming exactly to truth or to a standard and 3) able to give an accurate result. Other dictionaries refer to being “correct in all details,” or “faithfully representing the truth about someone or something,” or “precise; exact.”

Okay, those are good terms. So we’re looking for the truth. We want to trust the information we’ve purchased. But just who brings forth the truth, and how did they discover it? It’s this wrinkle that can be troublesome. In its folds often lie pesky things like estimates, probability, interpretation, and confidence levels. Oh, my, this is starting to get complicated. Before long, we’ll all be stuck in genetic quicksand, right? Relax. Follow along and we’ll soon lead you out of the valley of doubt and into the light of … well, come along and we’ll get there.

One key to arriving at the best possible information is to adjust our expectations. A few pieces of cautionary advice:

  • Don’t expect simple answers. The data behind ancestry estimates change over time as more people are added to reference databases.
  • DNA analysis is a tool, but don’t let it be the only one. You can test ancestry reports by checking the results against your family tree. Do you have relatives who emigrated from Bavaria or Poland? How does that compare to your DNA report? The DNA results, combined with traditional paper-trail genealogy, can be a powerful combination. Health and wellness DNA reports should be shared with your doctor, who can interpret them and advise if there is any cause for concern or more testing.
  • Direct-to-consumer DNA tests cannot diagnose diseases. Even a result indicating an increased risk for a disorder does not mean you will get it. Low risk does not mean you will be disease-free.
  • Be prepared for surprises. Ancestry tests sometimes reveal closely held family secrets (babies put up for adoption, one parent with no biological tie to one or more of their children, etc.). Unearthing this information can cause emotional distress and strain in the family.

With our definitions set and our expectations calibrated, we return to our original question: are home DNA tests accurate? The answer is … it depends. We can hear you groaning, giving yourself a forehead slap, followed by the sound of a deflating balloon. Pfffft. Ok, but “it depends” is the unvarnished truth. It depends on many things, such as the type of DNA test, the specific genetic markers being analyzed, quality-control procedures at the lab, and the kind of reference populations to which they compare your DNA. These things can vary from company to company, meaning results can vary — sometimes quite a bit.

Put Odds in Your Favor

The best way to ensure accurate DNA test results is to buy the test kit from a company that follows defined protocols for processing DNA, has strict quality-control procedures and communicates your information in an easy-to-understand manner. The best companies will have these attributes:

  • Have or use a CLIA-certified laboratory. The Clinical Laboratory Improvement Amendments of 1988 (CLIA) are regulations and standards that originated in the United States to ensure laboratory quality and information accuracy. “It can be difficult to determine the quality of a genetic test sold directly to the public,” reads the genetics home reference guide from the U.S. National Library of Medicine. “Some providers of direct-to-consumer genetic tests are not CLIA-certified, so it can be difficult to tell whether their tests are valid.”
  • Be subject to oversight by government agencies such as the U.S. Food and Drug Administration. Companies like 23andMe have conducted research studies to support their requests to offer new types of DNA tests. Getting government approval is an important imprimatur because the data are examined by top experts in the field.
  • Have a large database of DNA samples used as ‘reference populations’ that help determine ethnicity and geographic origins. The two market leaders, Ancestry DNA and 23andMe, have 15 million DNA samples between them. They draw from those to find people whose history can be traced to a specific place. Databases with increasing numbers of DNA samples help these companies be more precise when estimating a customer’s heritage.
  • Don’t hype or oversell what their DNA tests can do. United States government agencies have been very critical of DNA tests that estimate chances of one day suffering from disorders like heart disease, diabetes or cancer. “…Risks of such diseases come from many sources, not just genetic changes,” reads a recent consumer bulletin from the U.S. Federal Trade Commission. “…Valid studies are necessary to prove these tests give accurate results.”

Testing, Testing, Testing

Author Mark Twain wrote in Chapters from My Autobiography, “There are three kinds of lies: lies, damned lies, and statistics.” Twain (1835-1910) might take a dim view if presented with a report on his own genome and how it relates to his family history and health. While there’s no need to be that harsh in our review of DNA tests, it’s not a bad thing to maintain a little of Twain’s skepticism. Let’s take another look at the various consumer DNA tests on the market. What do these tests claim, and will that information stand up to scrutiny?

Ancestry/Family Heritage — This is where it all started. Using DNA to estimate where a person’s ancestors came from proved to be an effective lure when the first ancestry DNA kits went on sale. Despite the meteoric rise in sales of ancestry kits, one genetics expert expressed doubts on the ability to predict ancestry back many generations. “When it comes to ancestry, DNA is very good at determining close family relations such as siblings or parents, and dozens of stories are emerging that reunite or identify lost close family members (or indeed criminals),” wrote Adam Rutherford in Scientific American. “For deeper family roots, these tests do not really tell you where your ancestors came from. They say where DNA like yours can be found on Earth today.”

The major companies in this market, such as Ancestry DNA, 23andMe, and Family Tree DNA, vary in how specific they are in reporting ancestor locations. Because we don’t have DNA samples from those who lived in the 1700s or 1800s, scientists use the DNA of living individuals whose ancestral histories are known. They build databases called reference panels and compare each customer’s DNA to what is in their databases.

Company scientists have cautioned that estimates in ancestry reports would change as the databases gathered more samples. Customers who send their DNA to two or more of these companies often find major differences in reports. Some companies have released major updates to their ethnicity estimates, based on larger databases of DNA samples. Our own Ancestry DNA results saw some noticeable changes with the new report.

  • Country/Region Original New
  • England, Wales & NW Europe 46% 52%
  • Ireland & Scotland 19% 25%
  • Scandinavia 14% —
  • Sweden (replaced Scandinavia) — 7%
  • Western Europe 4% —
  • Germanic Europe (replaced W. Eur.) — 14%
  • Eastern Europe 8% —
  • Baltic States (replaced E. Eur.) — 1%

As you can see, the makeup of some of the regions changed between the first report and the updated version. The percentages for others changed. Removed entirely from the updated report were Iberian Peninsula, Caucasus, European Jewish, and Finland/Northwest Russia. What caused the change? Primarily a huge increase in the size of the reference database, which went from 3,000 DNA samples to 16,000. Were the original data wrong? They were the best estimate based on the information available to Ancestry DNA at the time.

Dr. Catherine Ball, Ancestry’s chief science officer, wrote that the new estimates come “through a new computer algorithm that analyzes longer segments of genetic information, marking an important evolution in the way we interpret DNA data. Having built and expanded our DNA reference panel, we have a better understanding of genetic signatures globally, can break down geographic ethnicity estimates with greater specificity and give you a more detailed picture of your origins.”

We found a similar experience with our test results at 23andMe, between the original report and the newest estimates, which are based on more than 1,000 ancestry regions:

  • Country/Region Original New
  • British & Irish 53.1% 48.5%
  • French & German 21.9% 29.8%
  • Scandinavian 2.4% 7.2% (Sweden added)
  • Broadly NW European 17.8% 9.8%
  • Eastern European 0.5% 3.0% (Poland added)

In the newer report, 23andMe dropped Eastern European-Yakut and Balkan from our ancestry composition. We noted that 23andMe uses different region descriptions (British & Irish on 23andMe vs. separate regions of Ireland & Scotland, and England, Wales & Northwest Europe on the Ancestry DNA report. These differences, which are also found on other companies’ ancestry reports, can make comparisons between tests difficult. Family Tree DNA, for instance, uses broad geographic regions such as “BThe ritish Isles” and “Southeast Europe.” The 23andMe reference panel currently includes more than 13,000 DNA samples, made up from 23andMe customers public data such as the Human Genome Diversity Project.

There is one important feature of the 23andMe ancestry reports that is easy to overlook. In the ancestry composition report you have to look for a link, “Read More in Scientific Details.” The details page lists all of the populations for which your DNA was tested. Matches are listed as “likely match,” “possible match” and “not detected.” In our results, Sweden at 7.2% was just a possible match. At the bottom of that page is the answer. A little toggle box with the heading “Select Confidence Level.” By default, 23andMe composition reports are set at 50% confidence level. That means 23andMe scientists have 50% confidence that their estimates are correct. Whoa. It seems quite odd that at 50% confidence they report ancestry populations with decimal points.

You can select a higher confidence level using a drop-down menu. Confidence levels include 50-90% in 10% intervals. Unfortunately, this does not change the report numbers visible on the page. So it’s not easy to see how your ancestry composition would change at, say, 90% confidence. After selecting the confidence level, you have to download the raw DNA data, which is exported into a spreadsheet. From there the average customer will find the information a jumble, listing start and end points on various chromosomes. We tested this feature on a desktop computer using two web browsers, and on tablet and smartphone using the 23andMe mobile app. The only way to access ancestry composition at higher confidence levels is to download the raw data. This isn’t helpful.

You have to hop on over to the “Chromosome Painting” section, which shows color-coded chromosome maps and how the data change at different confidence levels. On the chart, the 50% default confidence level is listed as “speculative.” So, we find the experts are 50% confident in their speculation. What to make of this? The 50% confidence level allows 23andMe to show you more detail, which of course all customers want. This detail could well turn out to be 99% accurate as the DNA comparison databases grow. The key is to understand what you’re getting can’t be written in stone. Here’s how our ancestry composition stacked up at 50% confidence vs. 90% confidence levels:

  • Country/Region 50% Confidence 90% Confidence
  • (Speculative) (Conservative)
  • British & Irish 48.5% 10.8%
  • French & German 29.8% 1.3%
  • Scandinavian 7.2% —
  • Broadly NW Euro. 9.8% 64.2%
  • Eastern European 3.0% 1.3%
  • Broadly European 1.4% 21.5%

This chart doesn’t generate quite the same excitement. “Wow, I’m 64 percent Broadly Northwestern European!” Um, no. More speculative data produce more possibilities for precise countries and regions. The system is a work in progress. It will be updated and refined.

The new 23andMe reports have some interesting features using color-coded maps to explore ancestral regions. In our report, when we clicked on the supplied map of Ireland, up came a detailed country map, indicating in color tints the areas with the strongest evidence of recent ancestors. Darker tints indicate stronger evidence of ancestry. The map allows you to click on any of the counties in Ireland and bring up an even more detailed map. This is a great feature.

When you take an ancestry-based DNA test, spend time poking around every corner of the results. Read about the reference panels, which will be constantly upgraded. Look for information on confidence levels and how the scientists arrive at your ancestry composition estimates. Just realize that even though the most advanced science is used to analyze your DNA and estimate your ancestry, the system is still fairly new and growing. Ancestry DNA puts it quite well on its web site: “Your DNA doesn’t change, but the science we use to analyze it does.”

  • Health and Wellness — A newer entry into the home DNA test market, health and wellness reports are a more controversial compared to their ancestry counterparts. There are a number of major types of health-based DNA tests:
  • Traits — These examine your physical appearance such as eye color, body hair, dimples, cleft chin, freckles and even the texture of your earwax.
  • Carrier Status — This type of test analyzes if you carry genetic variants for diseases you could pass to your children, such as cystic fibrosis or certain types of muscular dystrophy.
  • Medical Predisposition — Your DNA is scanned for genetic variants that are in some cases associated with increased risk of developing diseases like Parkinson’s, late-onset Alzheimer’s or age-related macular degeneration.

In highly regulated markets like the United States, direct-to-consumer DNA health tests have come under increased government scrutiny. The U.S. Food & Drug Administration regulates home DNA tests for moderate- to high-risk medical purposes and reviews company claims to determine their validity. The agency looks at accuracy (how well a company’s laboratory can detect the variants involved in disease) and how it explains and interprets that information for customers.

To date, only one company, 23andMe, has gotten FDA approval to market tests for genetic predisposition to certain diseases. In 2017, 23andMe was authorized for tests related to Parkinson’s disease, late-onset Alzheimer’s, celiac disease, hereditary hemochromatosis and numerous other disorders. In 2018, the company received approval for tests to identify three mutations in the BRCA1 and BRCA2 breast cancer genes. More recently, 23andMe secured authorization for tests for DNA variants that could be associated with how well a patient metabolizes some medications, and the most common variants influencing a hereditary colorectal cancer.

The 23andMe health test suite includes nine genetic health risk reports, 44 carrier-status reports, 31 traits reports and eight wellness reports. Futura Genetics offers a report on 28 diseases and medical conditions, including diabetes, heart disease and various types of cancer. Internationally known Mayo Clinic recently teamed with Helix to enter the market with its GeneGuide DNA test, which explores disease risk, carrier screening, health traits and medication response.

Some test-kit vendors, such as EasyDNA, market tests that claim to predict your percentage risk of getting diseases such as prostate cancer, peripheral artery disease, lung cancer, colorectal cancer and many other disorders. It does not sell these kits in the United States. The FDA says these types of kits, reports and claims must undergo FDA review before they can be sold in the United States. Many other countries do not have such restrictions.

There is no magic guide to tell which companies and which DNA tests are most accurate and which are not. The best way to ensure valid test results, in addition to the steps suggested earlier, is to look for companies that have published research to back up claims that their tests show what they purport to show. Experts encourage anyone using a home DNA test for health to talk to their doctor or a genetic counselor, since these tests are not diagnostic and are prone to misinterpretation.

Lifestyle — Some of the newest direct-to-consumer DNA tests are so-called lifestyle or fitness tests that purport to show food sensitivity, the best approaches for skin care, the optimal diets, the best exercise routines, and even wine preferences. Some of this kind of information is included in the traits section of health DNA tests from companies like 23andMe, but there is a growing number companies marketing dedicated home DNA lifestyle tests.

HomeDNA markets healthy weight, skin care, and food & pet sensitivity tests. Helix, the lab that handles the Geno 2.0 deep ancestry tests by National Geographic, has rolled out a suite of wellness and entertainment tests. These include heart health, metabolism, diet, sleep insights and more. MiaDNA offers diet/nutrition, exercise/fitness and wellness/lifestyle tests. A number of brands list a disclaimer in their marketing materials that their information is for recreational and informational purposes only.

This category of home DNA test gets a bit sticky, so extra caution is warranted. They are not subject to government oversight in the United States, so that eliminates one layer of review. Take these tests more as entertainment than hard science and you can protect yourself from disappointment. But caveat emptor (buyer beware), you could easily spend hundreds of dollars taking these a la carte tests. Like other DNA tests, the potential issue could be not with the science (if the labs are certified), but with the interpretation and recommendations. Look for sample test reports, especially ones that give clear explanations of what the results mean and how they were generated. It’s also smart to consult a doctor, dietitian or other health professional when considering new diet or exercise routines.

Paternity — DNA tests are usually very good at determining close familial relationships such as parents or siblings. Home DNA paternity tests are best for simply clearing doubts about who a child’s father is. They have no legal validity. Collection of samples is not done in a secure setting, so there is no way to verify that the DNA really came from the people named on the vials. There are also issues of chain of custody that render this type of test useless in court. Test kits cost from $75 to $200 or more. Some companies sell test kits in retail stores for even lower prices (such as $14.99), but after sample collection there is a lab fee that can be more than $100. Test kits typically use buccal (cheek swabs) to obtain cells for DNA extraction and analysis. HomeDNA sells its paternity test in retail stores and offers standard two-day turnaround for results, with faster delivery available for an extra fee.

Some companies do offer court-admissible DNA tests, although sample collection and shipping are handled by independent laboratories. It is advisable to consult an attorney if you plan to use DNA testing to make a paternity claim or for seeking child support or government benefits.  Court-ordered DNA paternity tests are typically collected directly by approved third parties, who maintain chain of custody on the way to the testing laboratory. Two tests are often done by different labs as an added security and accuracy measure.

For judging accuracy of home paternity DNA test kits, look for the prerequisites outlined in this article for certification and adherence to laboratory standards and procedures. Look for kits that test a higher number of genetic markers. Some kit vendors say their paternity tests are 99.9% accurate if the tested person is the biological father. Considering the ramifications of such home testing, doing a second test would be a wise move.

Pet Breeds and Health — The burgeoning popularity of DNA tests has even reached into the animal kingdom. Pets around the world are barking with joy to learn their own ancestry (breed), health information and more. It’s the human home-DNA test world, only with four paws and fur. If you’re dying to know if Fido is a Bichon Frise or a Toy Poodle, this is the kit for you. Our standard advice for other DNA tests applies here as well, so look for companies with accredited labs, expertise in veterinary science and a large reference database of DNA samples. Test kits typically use a cheek swab to obtain cells for DNA analysis.

Embark offers a $199 dog DNA test that covers health (165 genetic conditions), breed identification, ancestry (back to great grandparents) and, if you can believe it, a canine relative finder. Embark is endorsed by the Westminster Kennel Club. It tests 200,000 genetic markers to develop its health, breed and ancestry reports. Reports are similar to the human variety. A sample report on the Embark web site shows Pepper, who is 52.1 Labrador Retriever and 47.9% poodle. Another doggo, River, is 100% purebred Australian Shepherd. Embark tests for more than 250 dog breeds.

Wisdom Panel offers a test kit primarily for breed detection, but including screening for exercise-induced collapse and drug sensitivity. The cost is $84.99. It also offers a combined breed and disease detection test for $149.99. Wisdom Panel tests for more than 350 breeds, and compares Fido’s DNA to a reference panel of 15,000 breed samples.

Bottom line

As we’ve discovered, sometimes the simple questions have complex answers. The bottom line is the accuracy of home DNA tests varies. You’re safest looking for the brands with lab certifications, peer-reviewed research, easy-to-understand written materials, and terms/conditions that don’t over promise and honestly state what their tests can and cannot do. The science behind many of these home kits is solid. Technology is improving all the time. A little consumer education will help test kit customers learn more about themselves — and be able to trust the results.