Sibling DNA testing explained, full siblings, half siblings and what the results mean

What is a sibling DNA test?

A sibling DNA test compares the genetic profiles of two individuals to determine the probability that they share one or both biological parents. It is commonly used when direct parental testing is not possible.

Full siblings vs half siblings

Full siblings share both biological parents and therefore share approximately 50% of their DNA. Half siblings share only one biological parent and share approximately 25% of their DNA.

A sibling test can distinguish between these two relationships with a high degree of statistical confidence.

When is a sibling test used?

• Reconnecting with biological siblings after adoption or family separation

• Confirming a sibling relationship when a parent is deceased or unavailable

• Immigration and visa applications requiring proof of sibling relationship

• Inheritance and estate disputes

• Personal curiosity about biological family

How to improve accuracy

Sibling tests produce a statistical probability index rather than a definitive match. Including additional participants such as the biological mother significantly improves the accuracy of the result.

Understanding the results

Results are expressed as a Sibship Index. A value above 1.00 indicates a biological sibling relationship is more likely than not. A value below 1.00 indicates it is unlikely. Our team will explain your specific results in plain language.