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When samples are collected and processed correctly at an accredited lab, paternity testing is genuinely one of the more reliable tests in medicine — well over 99.99% accurate for confirming paternity, and 100% accurate for excluding a non-father. The honest caveat is in that first clause: “when collected and processed correctly.”
The Real Cause of Wrong Results Isn’t Bad Science
It’s worth being precise about this, because it changes what’s actually worth worrying about: the DNA science itself is extremely reliable and well-established. When results turn out wrong, the cause is almost always human error somewhere in the process — sample mislabeling, sample switching, contamination during collection, or in rare cases, deliberate fraud — not a flaw in the underlying testing method.
Mislabeling and Sample Switching
The most common real-world cause of an inaccurate result is samples or paperwork getting swapped between participants during collection or handling. In this scenario, the lab’s actual analysis is accurate — it correctly reads whatever DNA was in the tube — but the result gets attached to the wrong person because of a labeling error upstream of the lab. This is exactly why proper collection procedure, and for legal tests specifically, a documented chain of custody, matters as much as the lab science itself.
What Contamination Actually Does — and Doesn’t Do
Contamination happens when a sample picks up DNA from someone other than the intended person — two people handling the same swab, or a shared personal item submitted for a discreet test being an obvious example. Here’s the reassuring part that surprises most people: contamination usually doesn’t produce a wrong result. A competent lab detects a mixed DNA profile during analysis and flags it as inconclusive, requesting a new sample, rather than confidently reporting an incorrect answer. A silently wrong result from contamination is the rarer, worse-case scenario — the more common outcome is simply a delayed, redone test.
Close Biological Relatives Complicate Results
A genuinely tricky edge case: if the tested man has a close biological relative — particularly a brother — who could plausibly be the father, standard paternity testing can have real difficulty distinguishing between them, since close relatives share a meaningfully higher proportion of DNA than unrelated individuals. This isn’t a lab error; it’s a real limitation of the testing method in this specific scenario, and it’s worth flagging to the lab upfront if it applies, since additional or different testing may be needed to resolve it.
How to Actually Minimize the Real Risk
- Use an AABB- or ISO-accredited lab. Accreditation means the lab follows recognized protocols specifically designed to catch and prevent these errors.
- Follow collection instructions exactly — proper swabbing technique and avoiding cross-contact between samples meaningfully reduces the contamination risk described above.
- Use a chain-of-custody collection if there’s any chance the result matters legally — see our chain-of-custody guide for why this specifically protects against mislabeling and switching, the actual most common cause of error.
Paternity Lab uses accredited testing with the collection procedures described above — see our full Paternity Lab review for the honest details on their process and accuracy verification.
How accurate are paternity tests when done correctly?
When samples are properly collected and processed at an accredited lab, paternity testing is well over 99.99% accurate for confirming paternity and 100% accurate for excluding a non-father.
If a sample gets contaminated, does the test give a wrong answer?
Usually not — a competent lab detects a mixed DNA profile from contamination and flags it as inconclusive rather than reporting a wrong result. The more common outcome of contamination is a delayed, redone test, not a silently incorrect one.
What’s the most common actual cause of a wrong paternity test result?
Human error in sample handling — mislabeling or switching samples during collection — not a flaw in the underlying DNA science. This is exactly why proper collection procedure and chain of custody matter as much as lab accuracy.