How to Take a DNA Test: A Step-by-Step Guide

Taking a DNA test at home involves ordering a kit, providing a saliva or cheek-swab sample, mailing it to a lab, and waiting a few weeks for results. The process is straightforward enough that millions of people have done it from their kitchen tables, but the choices you make before, during, and after collection can affect both the quality of your sample and what you actually learn from it. The steps themselves are simple, yet the science behind them and the implications of the results deserve more thought than the cheerful packaging suggests.

Deciding What You Want to Learn

Before you order anything, figure out why you want a DNA test. The major consumer categories are ancestry estimation, relative matching, health-risk screening, carrier status for inherited conditions, and pharmacogenomics (how your body processes certain medications). Some companies bundle several of these together; others specialize. The U.S. Food and Drug Administration approved 23andMe to return select pharmacogenomic results to customers in 2018, and since then the menu of health-related insights available without a doctor’s order has expanded across the industry.¹ If you want medically actionable information rather than a fun ethnicity pie chart, pay attention to whether a company’s health reports have FDA authorization, because not all do.

Ancestry-focused tests compare your DNA to reference panels of people from different global populations and estimate the percentage of your genome that resembles each group. Health-risk reports look at specific genetic variants associated with conditions like breast cancer or Alzheimer’s disease. Carrier-screening reports tell you whether you carry a variant for a condition like cystic fibrosis or sickle cell disease that could be passed to children. These are genuinely different products even when they come in the same box, and which one matters most to you should drive your choice of company.

Ordering and Unboxing the Kit

Once you pick a provider, you order a kit online. It arrives by mail within a few days to a couple of weeks. Inside, you will find either a saliva collection tube or a cheek swab, along with a prepaid return envelope and instructions. Most major consumer companies use saliva tubes, but some clinical and pharmacogenomic tests use buccal (cheek) swabs instead.

You will also need to register your kit online. Every tube or swab has a unique barcode that links your physical sample to your digital account. If you skip the registration step, the lab has no way to connect results to you. Do this before you spit, not after, so you don’t end up fumbling with a barcode while holding a tube of saliva.

Collecting Your Sample

This is the part people overthink. If your kit uses a saliva tube, you uncap it and spit into it until the liquid (not the foam) reaches the fill line, then snap the cap closed. The cap typically releases a stabilizing solution that mixes with the saliva to preserve your DNA during shipping. If the kit uses a cheek swab, you rub the swab firmly along the inside of your cheek for the time specified in the instructions, usually 30 to 60 seconds per cheek.

Both methods work. Research comparing collection approaches found that saliva and cheek swabs produce comparable DNA quality and quantity for the kind of genotyping consumer tests perform.² That said, people generally prefer spitting into a tube over swabbing their cheeks, and studies show that whole-saliva samples yield more total DNA than swabs, even if both methods provide enough for a standard consumer test.³ One advantage of buccal swabs is that the collected DNA tends to be more stable over time, which can matter if the sample sits in transit longer than expected.⁴

Getting a Clean Sample

Kit instructions typically tell you not to eat, drink, smoke, chew gum, or brush your teeth for 30 minutes before collecting your sample. This advice is worth following, but if you accidentally had coffee 20 minutes beforehand, it is probably not a disaster. A study that tested saliva samples collected after participants consumed various foods and beverages found no meaningful difference in DNA quantity or quality compared to samples collected under ideal conditions.⁵ The collection devices are designed to be robust enough for real-world use outside a clinical setting. Still, following the manufacturer’s instructions gives you the best shot at a clean sample on the first try, and avoiding a redo is worth the half-hour wait.

A few practical tips people wish they had known: hydrate well before collection because dehydrated saliva is thick and foamy, and foam does not count toward the fill line. If you are having trouble producing enough saliva, gently rubbing the outside of your cheeks or thinking about sour food can help stimulate flow. Do not let someone else handle the swab or tube interior, as contamination from a second person’s DNA can cause the lab to reject the sample.

Shipping Your Sample

Seal the tube or swab in the provided biohazard bag, place it in the prepaid mailer, and drop it in the mail. Once the cap is closed on a saliva tube, the stabilizing buffer inside keeps your DNA intact at room temperature for an extended period. Research on saliva specimens with stabilizing agents has found that they can be stored at ambient temperatures for months without degradation, which is far more forgiving than blood samples, which require freezing for long-term storage.⁶ So even if the package sits in a hot mailbox for a day or takes a week to reach the lab, your DNA is almost certainly fine.

That said, don’t leave the sealed kit sitting on your counter for weeks before mailing it. The sooner it reaches the lab, the better. Most companies provide tracking, so you can follow the package and will receive a notification when the lab begins processing.

What Happens at the Lab

Once the lab receives your sample, technicians extract DNA from the cells in your saliva or cheek swab. For consumer ancestry and health tests, the extracted DNA is placed on a genotyping chip, which reads hundreds of thousands of specific positions in your genome where people commonly differ from one another. This is not whole-genome sequencing; the chip checks known landmarks rather than reading every letter of your DNA. The process typically takes three to eight weeks from the day the lab receives your sample, depending on the company and current demand.

Some clinical tests go further. Whole-genome sequencing reads essentially every base pair and can detect a wider range of variants, including single-letter changes, small insertions and deletions, and even repeat expansions, though it takes longer and costs more.⁷ Most people ordering a consumer DNA kit at home will get genotyping, not sequencing, but it helps to know the distinction exists when interpreting what your results can and cannot tell you.

Reading Your Ancestry Results

Ancestry results arrive as a breakdown of estimated regional origins, often displayed as percentages on a colorful map. These estimates are generated by comparing your DNA to reference panels of people whose ancestry from specific regions is well documented. The composition of these reference panels matters enormously: if a company has a large reference panel for Northern European populations but a small one for Southeast Asian populations, the estimate for someone with Southeast Asian heritage will be less precise. This is why your ancestry percentages can differ between companies and why they sometimes change when a company updates its reference panel.

Ancestry estimates are just that: estimates. They describe statistical similarity to reference groups, not a definitive accounting of your family tree. If your results say you are 12 percent Scandinavian, that does not mean exactly 12 percent of your ancestors came from Scandinavia. It means that about 12 percent of the DNA markers the chip examined resemble the patterns seen in the company’s Scandinavian reference panel.

Relative Matching and What It Can Reveal

Most consumer tests also offer DNA relative matching. The platform compares your genotyping data against everyone else in its database and identifies people who share segments of DNA with you. The more DNA you share with someone, the more closely related you are. Close relatives like parents, siblings, and first cousins share large, easily detected stretches. More distant connections are harder to spot because they share much less.

Research on identical-by-descent segment sharing puts some useful numbers on this: about 98.5 percent of third cousins share at least one detectable DNA segment, but that figure drops to roughly a third for fifth cousins and less than one percent for eighth cousins.⁸ In practical terms, a DNA test is very good at finding relatives up to about second or third cousins. Beyond that, you are increasingly likely to miss connections entirely because the shared DNA is simply too small to detect reliably.

If you are taking a DNA test hoping to find biological family members, the size of the company’s database matters as much as the science. A person in a database of 20 million is more likely to find matches than someone in a database of two million. Some people test with multiple companies or upload their raw data to third-party comparison sites to cast the widest net.

Health Results and Their Limits

Health-risk reports flag whether you carry specific genetic variants associated with diseases. These reports can be genuinely useful for conditions with strong genetic links, like BRCA1/BRCA2 variants and breast cancer risk or the APOE-e4 variant and Alzheimer’s risk. Carrier-status reports tell you whether you carry one copy of a variant for a recessive condition, meaning you are unlikely to develop the condition yourself but could pass the variant to your children.

Here is where caution is essential: consumer genotyping chips test for a limited set of known variants, not every possible mutation in a gene. A negative result does not guarantee you are free of risk. You might carry a rare variant the chip was not designed to detect. And the raw data files that some companies let you download are even less reliable for health interpretation. A study analyzing variants reported in direct-to-consumer raw data found that roughly 40 percent of the flagged variants were false positives that did not hold up under clinical-grade confirmatory testing.⁹ If a consumer test flags a concerning health variant, the right next step is confirmatory testing through a clinical lab ordered by a healthcare provider, not panic.

The same principle applies to pharmacogenomic results. Even though the FDA has authorized certain companies to report how your genetics might affect your response to drugs like blood thinners or certain antidepressants, pharmacists and physicians are advised to seek confirmatory testing before making changes to any medication regimen.¹ Consumer-grade results are a starting point for a conversation, not a prescription change.

Privacy and Who Else Might See Your DNA

When you send your DNA to a company, you are handing over the most personal data you have. It is worth reading the privacy policy before you spit. Key questions include whether the company shares anonymized or de-identified data with researchers, whether you can opt out of that sharing, and what happens to your physical sample after testing. Some companies destroy the sample; others store it unless you explicitly request deletion.

Law enforcement access is a real consideration. Investigative genetic genealogy, in which police match crime-scene DNA against consumer databases to identify suspects through their relatives, has been used in over 200 criminal investigations.¹⁰ A review of 22 direct-to-consumer companies found that all of them told consumers that law enforcement access or legally compelled disclosure was possible, but only four of those companies explained how law enforcement should go about requesting access.¹⁰ The concern is not just about your own privacy. Because relatives share DNA, your decision to test can expose family members who never consented to anything.

The regulatory landscape is also unsettled. Researchers have called on legislators to create stronger protections for consumer genetic data and biospecimens, particularly as companies face financial pressures and the possibility of bankruptcy, acquisition, or policy changes that could change how stored data is handled.¹¹ In the United States, the Genetic Information Nondiscrimination Act protects against discrimination by health insurers and employers, but it does not cover life insurance, disability insurance, or long-term care insurance. If you are considering applying for any of those policies, testing positive for a high-risk variant could theoretically affect your options.

Preparing for Unexpected Results

This is the part of taking a DNA test that no step-by-step guide can fully prepare you for, but it would be irresponsible not to mention. DNA tests sometimes reveal information that upends a person’s understanding of their own family. The most common surprise is what genetic genealogists call a “not parent expected” result: discovering that a biological parent is not who you thought. This can happen through relative matching, when the database connects you with close relatives you did not know existed, or through ancestry results that do not align with your family’s narrative.

Research on people who have experienced these discoveries paints a consistent picture. The initial reaction is typically shock, followed by a cascade of grief, loss, and identity disruption. Many people describe the experience as a crisis that ruptured existing family relationships, particularly with the mother in cases of unexpected paternity.¹² Isolation, shame, and a lack of emotional support are common in the aftermath.¹³

People who encountered these surprises sought help from spouses, siblings, online peer-support communities, and mental health professionals. The peer communities were generally considered helpful, while therapists received mixed reviews; some were supportive, but others were described as ill-equipped to understand the specific nature of the experience.¹² If you have any reason to suspect your family history holds secrets, or even if you don’t, it is worth considering before you test whether you are prepared to handle a result that changes your understanding of who you are.

Special Situations That Affect Results

A few circumstances can complicate DNA testing in ways worth knowing about. Identical twins share virtually the same DNA, which means standard consumer tests cannot distinguish between them. If both twins are in the same database, their relative matches will overlap entirely, and any health results will be identical.¹⁴ Ultra-deep sequencing can pick up the tiny mutations that accumulate after twins split in the womb, but that technology is not available through consumer kits.

People who have received a bone marrow transplant carry two sets of DNA: their original DNA in most body cells and the donor’s DNA in their blood cells. Saliva contains some white blood cells, so a saliva sample from a transplant recipient can produce a mixed or confusing result. If you have had a bone marrow transplant, a cheek swab taken carefully from the inner cheek lining is more likely to capture your own epithelial cells rather than donor blood cells.

Very young children and elderly adults sometimes have difficulty producing enough saliva to fill a tube. For infants or toddlers, companies that offer pediatric testing usually provide swabs instead. For older adults, dry mouth from medications is a common obstacle. Saliva-based testing has been shown to work well in predominantly elderly populations when the stabilizing solution in the tube is properly activated, but collecting the minimum volume can take patience.⁶

After the Results Arrive

Results appear in your online account, sometimes with a notification email. Spend some time clicking through the interface before jumping to conclusions. Ancestry results often include a confidence range for each estimated percentage. Health results typically come with context about what each variant means and what your overall risk looks like compared to the general population. Read those caveats. A variant that sounds alarming in isolation may confer only a modestly elevated risk when placed in the context of your age, sex, and lifestyle.

If your health results flag anything you are concerned about, talk to a doctor or genetic counselor rather than spiraling through internet searches. Genetic counselors are specifically trained to help people interpret test results, weigh next steps, and put genetic risk into perspective alongside family history and other factors. Many can now be consulted via telehealth, and some consumer testing companies offer bundled or discounted genetic counseling sessions as part of their health-report packages.

For ancestry and relative matching, remember that the database is a living thing. New matches can appear for months or years after you test, as more people join the platform. You can choose whether to be discoverable to relatives, and you can adjust those settings at any time. Some people opt in enthusiastically; others decide, after reflection, that they would rather not be found. Either choice is reasonable, and neither is permanent.