Why Some DNA Tests for Relationships Are Inconclusive

Why Inconclusive DNA Test Results Happen—and What You Can Do

If you’ve taken a sibling DNA test, aunt/uncle (avuncular) DNA test, or a grandparent DNA test, you might expect a simple "yes" or "no" answer. But relationship testing works a little differently. Instead of giving a binary result, these tests use a statistical approach called a likelihood ratio, which calculates how much more likely the tested relationship is—compared to the individuals being unrelated. 

For example, a report might include a sentence like: 

“The DNA profiles of Individual 1 and Individual 2 were compared and statistical analysis was performed. Based on this analysis, the results are 1,000 times more likely if Individual 1 and Individual 2 are related as Grandparent/Grandchild rather than if they are unrelated.” 

However, because these tests only analyse a portion of a person’s DNA, some results may come back as inconclusive. This is more common in extended relationships where the expected DNA sharing is more variable. 

At AssureDNA, we’re here to help you understand what that really means—and guide you through your next steps.

Why Can a DNA Test Be Inconclusive? 

All DNA tests work by identifying shared genetic markers. Our standard peace-of-mind test uses 23 markers, which is usually enough to confirm direct relationships like paternity or maternity while maintaining the fastest turnaround time for you. 

But in more distant relationships—such as: 

…the amount of shared DNA is less consistent. For instance, biological siblings may share anywhere from 37% to 61% of their DNA. That’s why even if two people are genuinely related, the standard 23-marker test may not always produce a conclusive result. Each relationship type has an expected average DNA match (e.g., half-siblings typically share around 25%), but real-life genetics don’t always follow the average exactly.

How Do We Decide Whether a Result Is Conclusive? 

To issue a conclusive result, our lab needs to reach a minimum level of statistical confidence based on the DNA data. In most cases, especially for direct relationships like paternity, this threshold is easily met.

But with extended relationships like grandparents, aunts/uncles, or siblings, the amount of shared DNA varies more. That means in around 1 in 20 tests, the result falls into a grey area—we can see there may be a connection, but not with enough certainty to call it conclusive. 

When this happens, we don’t guess—we pause, explain the result clearly, and offer further testing to get you closer to an answer.

What Happens If My Result Is Inconclusive? 

If your result falls below the required threshold, here’s what we do next: 

1. Free re-analysis with additional markers 

We automatically expand the test to include around 50 markers, at no extra cost. This helps improve the resolution of the result and increases the chances of a definitive outcome. 

2. Optional upgrade to our Advanced Test 

If even the 50-marker analysis doesn’t produce a conclusive result, you’ll have the option to upgrade to our Advanced Test, which often examines around 600-markers. 

This test isn’t mandatory, but it is often the best way to resolve an inconclusive result—especially in cases involving grandparentage or other extended relationships.

Which Relationships Might Need the Advanced Test? 

We typically recommend the high-resolution test for: 

Our Commitment to You 

We understand how emotionally important your results can be. That’s why we promise to: 

Order a DNA Test Kit Today 

Whether you’re seeking a paternity test in the UK, a sibling DNA test, or simply answers for peace of mind, AssureDNA is here to help. Order your kit today or speak with our team for personalised guidance on choosing the right relationship test for your situation.