A DNA test is supposed to settle things. But sometimes the result lands and instead of closure, you get more questions. The numbers feel off. The conclusion doesn't match what you expected. Or the paperwork looks thin and you're not sure what it's actually telling you.
That instinct to double-check is worth listening to. DNA testing is highly accurate when done correctly — but "done correctly" covers a lot of ground: the lab's methodology, how many genetic markers were analyzed, how the samples were collected and handled, and whether the statistical math was performed properly. When any of those steps go wrong, a result can be technically valid and still misleading.
Here are five specific signs that a DNA test result may warrant a second opinion, along with what to look for and what to do next.
1. The Result Came Back Inconclusive
An inconclusive result is not the same as a negative. It means the test gathered data but could not reach a definitive conclusion either way — the person tested is neither clearly included nor clearly excluded as a biological relative.
This happens more often than most people expect, particularly in kinship tests. When you're comparing two indirect relatives — a grandparent and grandchild, two potential siblings, or an aunt/uncle and niece/nephew — the shared DNA signal is naturally weaker than in a direct parent-child test. The lab's statistical output (called a Combined Relationship Index, or CRI) may fall in a gray zone where it's above the threshold for exclusion but not high enough to confidently confirm the relationship.
In these cases, the right move isn't to accept the ambiguity. A well-equipped lab can expand the analysis. Additional autosomal STR markers can be added to sharpen the statistical picture. USDC's lab, for example, can analyze up to 28 genetic markers in total — the standard panel covers 23 autosomal STR markers, and up to 5 more unique markers can be added specifically when a kinship result lands in that inconclusive range and more statistical weight is needed.
If your report says "inconclusive," ask the lab explicitly whether additional markers can be run on the existing data — or whether a retest with expanded analysis is available.
2. The Lab Tested Too Few Genetic Markers
Not all DNA tests analyze the same number of genetic markers, and the difference matters more than most consumers realize.
The FBI's CODIS system — the national DNA database standard — moved to a minimum of 20 core STR loci in 2017. Labs that haven't updated their panels may still be working with fewer markers, and some lower-cost providers test as few as 15 or 16. The fewer markers analyzed, the wider the statistical uncertainty — meaning a result that looks definitive might be built on a thinner foundation than you'd want.
Industry standard for relationship testing today is 20 or more markers. Some pharmacy-partner labs still use fewer than 20 — it's worth asking before you buy. USDC's home paternity test can analyze up to 28 genetic markers: the standard run is 23 autosomal STR markers, which is enough to produce a probability of paternity at or above 99.9999% for true inclusions and an unambiguous 0% exclusion for true non-fathers. The additional markers exist as a reserve for kinship cases that need more statistical resolution.
If your existing result came from a lab that tested fewer than 20 markers and the result is anything other than a clean exclusion, a retest with a lab that runs a larger panel is reasonable due diligence.
What to check: Your DNA report should list the specific markers (loci) analyzed and the allele values at each one. If that table is missing, or if it shows fewer than 20 rows, that's a flag worth taking seriously.
3. The Report Doesn't Include Any Probability Statistics
A legitimate DNA relationship test report does more than label a result "positive" or "negative." It shows the math.
For paternity tests, the key figure is the Probability of Paternity — a percentage that reflects the statistical likelihood that the tested man is the biological father, compared to a random untested man from the same population. Reputable labs report this at 99.9% or higher for inclusions (often written as 99.99% or even 99.9999%) and 0% for exclusions. The report should also list the Combined Paternity Index (CPI), the underlying odds ratio.
For kinship tests, the equivalent figure is the Combined Relationship Index (CRI). A CRI above 1.0 supports the relationship; below 1.0 supports non-relationship. The further from 1.0, the clearer the conclusion.
If your report is missing these numbers — if it just says "father included" or "not a match" without showing the probability — you cannot assess how confident that conclusion actually is. A result with a CPI of 500 is much more statistically solid than one with a CPI of 12, even though both might be reported as "positive." Professional forensic genetics standards require labs to report these figures precisely so that the strength of the evidence is transparent.
Ask the lab for the full report with all statistical outputs. If they can't or won't provide it, that's a sign the methodology may not hold up to scrutiny.
4. There Were Problems With Sample Collection or Handling
DNA testing is only as reliable as the samples it starts with. Collection errors are one of the most common sources of inaccurate results — and unlike lab methodology errors, they often happen before the sample ever reaches the laboratory.
Common collection problems that can compromise a result:
- Contamination: Eating, drinking, smoking, or kissing within 30 to 60 minutes before swabbing can introduce foreign DNA into the sample. If a child's sample was collected shortly after breastfeeding, or if multiple people used the same swab, contamination is a real possibility.
- Insufficient sample: A swab that wasn't rubbed long enough or firmly enough may not collect enough cells for reliable analysis. Labs will usually flag a low-quality sample and request a resubmission — but not always.
- Improper storage or transit: DNA degrades in heat and moisture. A sample left in a hot car, a package that sat in a warehouse, or a swab that wasn't allowed to air-dry before being sealed can all produce degraded DNA that affects how clearly the alleles read at each marker.
- Wrong person swabbed: This sounds unlikely, but in high-stakes situations — child custody disputes, family estrangements — the possibility of a switched or substituted sample is real enough that many legal-context tests require witnessed collection by a neutral third party.
If any of these situations apply to your test, the result may be technically accurate to the samples received — but those samples may not accurately represent the people they were supposed to represent. A fresh collection with careful attention to protocol is the cleanest fix.
5. The Result Contradicts Reliable Medical or Family History
This one is more nuanced, but it deserves a place on the list.
Sometimes a DNA result lands in a way that flatly contradicts information you have strong independent reason to trust: documented medical history, known genetic conditions that run in a family, or well-established family records. A result that contradicts all of that isn't necessarily wrong — DNA can hold surprises, and family secrets do exist — but it warrants scrutiny before you act on it.
The clearest scenario: a paternity exclusion where the alleged father has an inherited condition that the child has also been diagnosed with, or where independent genetic testing (through a medical provider, for instance) pointed a different direction. When multiple independent data points conflict with a single test result, that result deserves a recheck.
A second opinion doesn't mean you distrust science — it means you're treating a high-stakes conclusion with appropriate rigor. Doctors get second opinions on pathology reports. Lawyers review contracts a second time before signing. The same logic applies here.
What to Do If You Need a Second Opinion
The process is simpler than most people expect.
- Gather your original report. Before ordering anything new, read the original report carefully. Look for the marker table, the CPI or CRI, the probability of paternity, and the lab's accreditation information. Note exactly how many markers were analyzed.
- Identify what went wrong. Was it an inconclusive result? A low marker count? A sample handling concern? Pinpointing the specific issue helps you choose the right retest — whether that's a fresh standard test, an expanded kinship panel, or a different collection protocol.
- Order a new test from a reputable lab. For a home retest, USDC's home paternity test and kinship tests analyze up to 28 genetic markers and return results in 7 to 10 business days from the time you place your order, with standard lab processing taking 2 to 3 business days once samples are received. If you're in a hurry, expedited processing is available during checkout.
- Follow collection instructions exactly. No eating or drinking for 30 to 60 minutes before swabbing. Let the swabs air-dry completely before sealing. Keep the package out of direct heat.
- Read the full report when results arrive. A reputable result will show every marker analyzed, the allele values at each one, and the probability statistics. If anything is missing or unclear, contact the lab directly.
One practical note: if the situation is likely to involve legal proceedings — child support, custody, immigration, or inheritance — a home test will not serve that purpose. For court-admissible use, work with a provider specifically credentialed and chain-of-custody equipped for that use. Home testing and legal testing are separate products with different protocols.
— Dr. Todd Lewis
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This article is part of our Understanding DNA Testing: How It Works and What to Expect guide.
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