How to Interpret an Inconclusive DNA Test Result

How to interpret an inconclusive DNA test result — practical next steps: add more markers up to 28, add the mother, test additional relatives, or check sample quality

You opened the report expecting a clean answer. Instead you got the word inconclusive. Take a breath. This is more common than most families realize, and in the majority of cases it is fixable without starting over from scratch.

This guide walks through what inconclusive actually means, why it happens, and the specific steps you can take next. It is written for the person holding the report right now, not for a lab tech.

What is in this guide

What "inconclusive" actually means

Every DNA relationship test comes down to a number. For paternity, that number is the Combined Paternity Index (CPI), which gets converted into a probability of paternity. For kinship (siblings, grandparents, aunts and uncles, half-siblings), the number is usually the Combined Relationship Index (CRI). Labs draw a line above which the result is called "supported" and below which it is called "not supported." Inconclusive is the zone in the middle.

Practically, that looks like this:

  • Paternity inconclusive: probability of paternity between roughly 95% and 99%, or a CPI sitting near the reporting threshold. A definitive inclusion normally reads 99.99% or higher, and a definitive exclusion reads 0%.
  • Kinship inconclusive: a CRI between about 0.1 and 10. Values well above 10 support the tested relationship. Values well below 0.1 argue against it. In between, the data supports neither conclusion strongly.

An inconclusive report is not a failed test. The lab did the work. The math just landed in a gray zone, and the honest answer is that the data available so far is not enough to commit to a call. That is not a bug in the report; it is the report telling you the truth.

Why inconclusive results happen

Four things account for the majority of inconclusive results.

1. Population genetics. When labs calculate a paternity or kinship index, they compare how often each marker combination shows up in the general population. If the tested individuals share ancestry from a smaller or more homogeneous population, more of their markers will match by coincidence, and the math produces a weaker signal. Two unrelated people from the same ancestral background can look genetically closer than two unrelated people from very different backgrounds. This is a well-documented issue in forensic genetics and is discussed in peer-reviewed literature on short tandem repeat (STR) marker interpretation.

2. Shared ancestry between "unrelated" individuals. If the tested alleged father is a close relative of the true father (a brother, an uncle, a cousin), the child will share a meaningful amount of DNA with him even though he is not the biological parent. Kinship math is especially sensitive to this. It is one of the top reasons a kinship test comes back in the middle zone.

3. Sample quality. DNA testing needs enough intact DNA on the swab to read all the markers cleanly. Light swabs (barely rubbed against the cheek), swabs collected right after eating or drinking, swabs stored in a humid bathroom before being sealed, or swabs that got wet in transit can all yield partial profiles. A partial profile means fewer usable markers, which means less statistical power, which pushes borderline cases into the gray zone. The MedlinePlus overview of DNA testing is a good primer on how sample handling affects results.

4. Kinship math has more variance than paternity math. A parent contributes exactly half their DNA to each child, so paternity math is anchored to a clean 1-in-2 inheritance pattern. Siblings, half-siblings, grandparents, aunts and uncles share a variable percentage of DNA — on average 50%, 25%, or 12.5%, but with real spread around that average. Two full siblings can share anywhere from about 38% to 61% of their DNA. That biological variability is why kinship tests need more markers, more relatives tested, or both to reach a definitive answer.

Your next steps, in order

Work through these in sequence. In most cases, one of the first two moves resolves the report.

Step 1: Ask the lab to add the extra markers

USDC's lab runs 23 unique autosomal markers on a standard kinship case. When a kinship result comes back inconclusive, the lab can extend the same case up to 28 genetic markers using the DNA already on file. Those extra markers usually provide enough additional data to shift the CRI out of the gray zone in either direction. Call or email customer service, reference your case number, and ask for the extended marker panel on your existing case. This is not a new order. In many cases there is no additional home kit needed.

Step 2: Add the mother (paternity cases)

If your inconclusive result is on a paternity case and the mother was not part of the original test, this is almost always the highest-leverage move. When the mother is tested, the lab can subtract her contribution from the child's genetic profile. Whatever is left in the child came from the biological father. That single change turns most borderline paternity reports into a clear inclusion or clear exclusion.

USDC's home maternity test is $129 and uses the same kind of cheek swab collection as the paternity kit. Once samples arrive, the lab combines them with the existing case data and re-runs the calculation.

Step 3: Test additional relatives (kinship cases)

Kinship results get stronger when more of the family is on the report. If you are running a sibling test and the result is inconclusive, adding a parent (either one) sharpens the analysis substantially. If you are running a grandparent test, adding the second grandparent, an aunt, or an uncle on the same side helps. Every additional confirmed relative tightens the statistical picture.

USDC's home sibling, grandparent, and aunt and uncle kits are $139 each. You can order a second kit for the additional relative and have the results combined with the original case on file. The kinship DNA testing overview walks through which relatives make the most difference for which kind of case.

Step 4: Re-collect if the samples were borderline

If the lab's notes on your report mention low DNA yield, partial profile, or a specific participant with weak sample quality, ask about re-collecting only that person's swabs. The lab can send a replacement collection card or you can order a fresh kit. When you re-collect, follow the instructions carefully:

  • No food, drink, gum, or cigarettes for at least 30 minutes before swabbing.
  • Rub each swab firmly against the inside of the cheek for a full 30 seconds. You are trying to collect cheek cells, not saliva.
  • Air dry the swabs at room temperature before sealing.
  • Ship the same day if possible. Delays in a hot mailbox degrade DNA.

Most sample-quality retests come back conclusive.

Paternity math vs. kinship math

It helps to understand why paternity tests almost always come back with hard numbers and kinship tests come back in the gray zone more often.

Paternity has a fixed genetic relationship. The father either contributed one allele at each marker or he did not. That contribution is deterministic, so the lab is comparing the child's markers against a defined pattern. When the alleged father is truly the father, the numbers snap to 99.99% or higher very cleanly. When he is not, they drop to zero.

Kinship testing does not have that clean inheritance pattern. Full siblings share half their DNA on average, but the actual number for any given pair varies. Two brothers can share more DNA than average or less. The National Library of Medicine's summary on inheritance patterns covers the biology behind that variability. The upshot: kinship results are inherently noisier than paternity results, and that is exactly why the lab has the ability to add markers on kinship cases that come back inconclusive.

You can read more about the paternity side of the math in the paternity testing overview.

If the DNA test is for a legal purpose — a custody hearing, a child support case, an inheritance claim, an immigration filing — the standard home kit is not the right tool. Home DNA tests are collected by the family, which is fine for personal knowledge but not for the chain-of-custody requirements a court will ask about.

For legal use, work with a provider specifically credentialed for court-admissible testing. That process involves an independent sample collector, verified identification of each participant, chain-of-custody documentation from collection through analysis, and a lab that is set up to defend its process in court. It is a different service with different infrastructure and different pricing. If your report is inconclusive and you also need it to be legally usable, do not try to convert the home result. Start fresh with a legal-use provider so the entire chain of custody is clean from the beginning.

What to expect from a retest

Timelines depend on which path you take:

  • Extra markers on existing samples: 2 to 3 business days of lab processing once the request is logged. No shipping delay because the DNA is already at the lab.
  • Adding a new participant (mother, additional relative): 7 to 10 business days standard order-to-results, including shipping the kit out and getting the completed swabs back. Once at the lab, processing is again 2 to 3 business days.
  • Full re-collection due to sample quality: similar 7 to 10 business day window.

Expedited processing options are available during checkout if the timeline is urgent.

Ask the lab, when you request the retest, whether the amended report will be issued as a new document or as an update to the existing case. Either way, keep the original inconclusive report. If a court or an attorney ever asks about the case history, having both documents is cleaner than trying to reconstruct what happened.

A note on what inconclusive is not

Inconclusive is not a soft "no." It is not the lab hedging. It is not a signal that the tested individuals are secretly related in some way you have not considered. It is a statistical statement that the data collected so far is not strong enough to commit to an answer, and that more data — more markers, more relatives, or cleaner samples — is the right next step.

Most families who reach out about an inconclusive report walk away with a definitive answer within a couple of weeks. It is a bump in the road, not a dead end.

— Dr. Todd Lewis

Common questions

What does inconclusive mean on a DNA test?

The result landed in the statistical gray zone. On paternity tests, that is usually a probability of paternity between roughly 95% and 99%. On kinship tests, that is usually a Combined Relationship Index between 0.1 and 10. The lab needs more data before committing to a call.

Can I retest with the same sample?

Usually yes. If the DNA on file is still usable, the lab can run additional markers without a new collection. If the sample was low quality, the lab will ask for fresh swabs.

Does adding the mother help?

On paternity cases, yes — often dramatically. It lets the lab isolate the paternal contribution to the child's profile.

How much does it cost to run more markers?

Extending an existing kinship case from 23 to up to 28 markers is handled by the lab on the original case. If additional participants are needed, a paternity kit is $79, a maternity kit is $129, and a sibling, grandparent, or aunt and uncle kit is $139.

How long does a retest take?

Extra markers on existing samples: 2 to 3 business days. New participant added: 7 to 10 business days order-to-results.

Sources

0 comments

Leave a comment

Please note, comments need to be approved before they are published.

As Featured In
USA TODAY CBS NBC FOX ABC
View all 318 media placements →