A DNA sibling test can be used to determine the likelihood of two individuals having the same parents in common. It is mostly applicable in situations where the alleged parents are unwilling or unable to participate in a DNA paternity test. In the event where the alleged parent is available of course the preferable option would be a direct comparison through a DNA Paternity Test.

The DNA sibling testing can therefore be used to determine the likelihood of two or more individuals being full siblings, half siblings or sharing no biological relationship meaning being not related. Full siblings by definition have two biological parents in common (the mother and father), whereas half siblings have only one parent in common (either the mother or the father).

The DNA sibling test is conducted by examining the number of shared genetic markers between the individuals tested to determine the probability of a biological relationship existing between the people. The aim of the test is therefore to analyse the degree of shared DNA and to apply a scientific statistical analysis to deduce any possible biological relationship. The stronger the commonality of the DNA shared means the greater the probability of a biological relationship existing.

Due to the laws of genetic inheritance, true biological siblings can vastly differ in how similar or dissimilar their genetic profiles are. Some sibling may share many genes in common, whereas others may have inherited different genes from each parent, and therefore may not appear to have a lot in common.

Due to the above, it is therefore strongly recommended when undergoing a sibling analysis especially a half sibling test, to include any parent (normally the mother) as this will help improve in the comparison and interpretation of the results.

In specific cases, even in the absence of a parent being tested, the DNA laboratory is able to produce accurate results due to the nature of the testing methodology used in the laboratory. These cases include testing the Y-chromosome which is suitable for male to male siblings; Y chromosome is transferred through the direct male lineage whilst the X-chromosome is suitable for female to female siblings with the same potential father and different mothers. Mitochondrial DNA can test both male and female siblings through the maternal lineage).

The reasons for resorting to DNA Sibling Testing are many. However, some of the most common cases include:

- Adopted children, or siblings that have been separated, who eventually find their alleged siblings but the parents are deceased;

- Siblings who have doubts about their real paternal father, but the parents are unwilling to participate in the test;

- Claims on inheritance by an individual claiming to be related to the children of the deceased.

Before embarking on a DNA Siblings Test it is important to identify who is available for testing as this will assist the DNA laboratory to decide which DNA test is most applicable to your case. There can also be various stages of testing with additional people included in the testing if the first results do no yield a satisfactory result. Also in the case of minors (16 or 18 years of age depending on country of location) permission from the legal guardians may be required.