Definition
Siblingship index
The siblingship index is a statistical likelihood ratio comparing the probability that two individuals are full or half siblings against the probability that they are unrelated. AABB-accredited laboratories report both the index and a probability percentage.
Also known as: Sibling DNA test, Sibling index
Related: STR analysis, Half sibling test, Full sibling test
What is sibling DNA testing?
Sibling DNA testing analyzes shared genetic markers between two individuals to determine whether they share one or both biological parents. Full siblings share both parents and approximately 50% of their DNA on average. Half siblings share one parent and approximately 25%. Including a known parent in the test substantially increases statistical confidence.
When is sibling testing used?
Sibling testing is most often used to establish paternity when the alleged father is deceased, missing, or unwilling to test. It is also used in immigration cases (often paired with embassy coordination), inheritance and estate proceedings, and personal peace of mind for family members who suspect a half or full sibling relationship.
How does sibling DNA testing work?
Call (866) 873-0879
We discuss your situation and recommend the right test (full vs. half, with or without parent).
Visit a collection site
Each participant provides a buccal swab at an AABB-accredited site, or via at-home kit for personal testing.
AABB lab analysis
20+ STR markers analyzed to compute the siblingship index.
Receive results
Standard 1 to 3 business days. Rush processing available.
Compare sibling test options.
Sibling test options
| Test | Best for | Participants | Cost range |
|---|---|---|---|
| Full sibling | Two individuals who likely share both parents | 2 (plus a known parent improves accuracy) | $299 to $399 |
| Half sibling | Two individuals who likely share one parent | 2 (plus a known parent strongly recommended) | $329 to $429 |
| Sibling with reference parent | Highest statistical confidence | 3 | $399 to $499 |
Questions about which option is right for you? (866) 873-0879.
How accurate is sibling DNA testing?
Sibling DNA testing is most accurate when a known biological parent is included. Without a parent's sample, results report a statistical probability with a range of confidence. Including the mother's sample typically pushes confidence above 99% for confirmed full or half sibling relationships. Our AABB-accredited lab uses 20+ STR markers and produces a court-admissible certified report when chain-of-custody is followed.
Sibling DNA testing accuracy is significantly improved when a known biological parent is included in the test, allowing the laboratory to compute the siblingship index with confidence above 99% for confirmed full or half sibling relationships.